Hereditary amyloidosis continues to hold a prominent position in the minds of students of amyloid. Besides presenting models for studying the role of protein structure, expression, and metabolism in the mechanism of amyloid formation, the hereditary amyloidoses allow correlation of these basic factors with clinical observations on phenotypic expression, genetic transmission, and epidemiology. This makes hereditary amyloidosis a valuable model for the study of cell processes that may be common to many forms of amyloidosis. Mutant forms of plasma transthyretin continue to be the most common cause of hereditary amyloidosis. Since the last edition of this text, the number of mutations in transthyretin that are associated with systemic amyloidosis has increased to 73. Increased numbers of mutations in other proteins associated with hereditary amyloidosis have also been discovered, including 8 mutations in apolipoprotein A-I, four in fibrinogen Aα-chain, two in lysozyme, two in gelsolin and one in cystatin C. Several mutations in the Alzheimer β-APP protein result either in cerebral amyloid plaques or cerebrovascular Congophilic angiopathy. Mutations in the prion protein are associated with familial Creutzfeldt-Jakob disease and Gerstmann-Sträussler-Scheinker syndrome, which show amyloid fibril deposits. In addition, mutations in proteins presumed to be involved in the metabolism of normal amyloid fibril precursor proteins have been discovered, including mutations in presenilin I and II which cause Alzheimer plaque formation from normal β-APP. Similar genetic factors may be involved in the amyloid formation from normal apolipoprotein A-I and transthyretin. It is obvious that the hereditary amyloidoses are truly worldwide in distribution and that they affect a much larger number of families than ever previously considered.
The Transthyretin Amyloidoses (MIM 176300)
Most of the autosomal dominant amyloidoses characterized thus far are associated with variants of plasma transthyretin. So far, 73 mutations of transthyretin have been described, and there is likely to be more. To understand the pathogenesis of these forms of amyloidosis better, it is important to review the properties of transthyretin. Transthyretin is a normal plasma protein. It was originally called “prealbumin” or “thyroxine-binding prealbumin” because it migrates ahead of albumin on standard protein electrophoresis.127 However, it has no structural relationship to albumin.128 The name transthyretin (TTR) was coined because of the transport properties of the protein, which binds both thyroxine and retinol-binding protein (RBP).129 The term transthyretin is relatively universally accepted and is in general use. However, any literature review will find many of the significant articles under the name prealbumin.
Plasma transthyretin is synthesized by the liver in a constitutive manner as a single polypeptide chain of 127 amino acid residues.130,131 The primary structure has been known since 1974, and the secondary, tertiary, and quaternary structures were defined by x-ray diffraction.132 The entity circulating in plasma is a tetramer (M r = 55,000) composed of four identical monomers44,132 (Fig. 209-6). Two monomers noncovalently combine to form a stable dimer, and then two dimers associate to form the tetramer with twofold symmetry. Down the center channel of the tetramer are two binding sites for thyroxine, although binding studies suggest that these sites show negative cooperativity.133 Transthyretin also binds retinol saturated RBP (M r = 21,000) to provide transport of vitamin A without loss of the small RBP molecule through the kidney.134 RBP binds to the outside surface of transthyretin involving the isoleucine at position 84 and, while there are four potential binding sites on each tetramer, x-ray crystallography of the transthyretin and RBP complex shows that binding of one RBP molecule to the tetramer restricts binding of a second molecule to that side of the tetramer.135-137 Therefore, only two molecules of RBP can bind to one transthyretin tetramer. The transthyretin concentration in plasma normally ranges from 20 to 40 mg/dl and has been found to be significantly depressed in individuals with malnutrition. The plasma concentration also decreases at times of acute or chronic inflammation, and, therefore, transthyretin has been called a negative acute-phase protein. Plasma levels are also significantly depressed in many patients with the transthyretin amyloidoses, but the reason for this is unclear.138-140 The single gene for transthyretin is located on human chromosome 18.141 Most individuals with transthyretin amyloidosis have been found to be heterozygotes having one normal transthyretin allele and one variant allele. Expression of the two alleles is probably equal, but most studies have shown more of the normal gene product in the plasma than of the variant.142,143
Computergraphic model of the transthyretin tetramer based on x-ray diffraction data.144 Thyroxine binds to the central cavity. Rentinol-binding protein-vitamin A binds to the outside of the tetramer with amino acid Ile84 being central to the binding (arrows). Only two molecules of retinol-binding protein bind to one transthyretin tetramer because each molecule of retinol-binding protein (21,000 daltons) blocks the second potential binding site on that side of the tetramer.137
Transthyretin has extensive β-structure; the monomers have eight β-chains arranged in an antiparallel configuration in two planes (Fig. 209-7). This configuration would appear to predispose the protein toward amyloid fibril formation. Each of the amino acid substitutions that has been identified in variant transthyretins associated with hereditary amyloidosis can be hypothesized to alter the surface topography of the molecule.144 This alteration presumably would favor aggregation and fibril formation; however, no clear unifying structural change has been noted. The identification of several transthyretin variants that do not predispose to amyloid formation has not helped clarify this problem.145,146
Subunit structure of transthyretin. A, Antiparallel β-structure of transthyretin. Eight β-strands are arranged in two parallel planes. The approximate locations of eight of the mutations associated with amyloidosis are indicated. These include the mutation (Arg10) closest to the N-terminal and the mutation (Ile122) closest to the C-terminal. These two mutations are at the ends of the ordered β-strand structure. B, Two prealbumin monomers associate to form a dimer. Two dimers then associate to give the tetramer depicted in Fig. 209-6. (A modified from and B from Richardson JS: Adv Protein Chem 34:270, 1981. Used with permission.)
The transthyretin cDNA sequence has been reported by a number of laboratories,141,147,148 and the complete nucleotide sequence of the transthyretin gene in humans has been reported by two laboratories (GenBank NM_000371) (Fig. 209-8).149,150 The human gene has four exons (Fig. 209-9). Exon 1 codes for a 20-residue signal peptide and the first three amino acids of the mature protein, exon 2 codes for residues 4 to 47, exon 3, residues 48 to 92 and exon 4, residues 93 to 127. The proximal upstream 5′ region has sequences similar to those for binding the glucocorticoid receptor. However, the mouse prealbumin gene appears to have additional regulatory sequences about 2 kb upstream from the coding regions.130,151 Transthyretin mRNA has been identified in choroid plexus of rats152-154 and humans155 and also in retina, so synthesis is not exclusively hepatic. It is unlikely that extrahepatic transthyretin synthesis plays a role in the systemic manifestations of amyloidosis, but leptomeningeal involvement may be related to intracranial synthesis, and vitreous amyloid may possibly be the result of local gene expression.
Nucleotide sequence of transthyretin cDNA and protein amino acid sequence. Mutations shown include 66 associated with amyloidosis and 9 not associated with amyloidosis (indicated by *). Gly47Arg has been reported with both CGG and AGG codons (indicated by **). For recent mutation reports see Table 209-2.
Drawing of human transthyretin gene showing four exons. Twenty-seven mutations associated with amyloidosis have been identified in exon 2; 32 in exon 3; and 14 in exon 4. The recognition sites for PvuII are indicated (P) to show the DNA fragments generated in the Southern blot test for the Ala60 gene (see Fig. 209-16).
Autosomal Dominant Transthyretin-Associated Amyloidosis Syndromes
Most of the autosomal dominant amyloidoses have peripheral neuropathy as a major clinical manifestation. Thus, these disorders have also been called “familial amyloidotic polyneuropathy” (FAP). In the past, clinical classification of the syndromes was based on whether lower-extremity or upper-extremity neuropathy was the presenting symptom.156 This criterion is less valid now, because the upper-extremity neuropathy, which is really a compression neuropathy from the carpal tunnel syndrome, has been seen in many of the recently described kindreds, sometimes before and sometimes after involvement of the lower extremities (Fig. 209-10).
Kindred with hereditary transthyretin amyloidosis associated with variant transthyretin showing the typical autosomal dominant pattern of inheritance. ▪ = biopsy proven; □ = presumed affected; ⋄ = multiple sibs, sex unspecified.
The Portuguese neuropathy (FAP type I) shows the classic and most common features of hereditary amyloidosis (Fig. 209-11). The clinical disease usually starts in the third or fourth decade, although the onset of symptoms may be delayed until old age. The disease progresses over 10 to 20 years with peripheral sensorimotor neuropathy, autonomic neuropathy, and varying degrees of systemic amyloid involvement. The neuropathy starts in the lower extremities with paresthesias and often hypesthesia, which can be debilitating. Autonomic neuropathy is an early feature, and patients may present with sexual impotence or gastrointestinal dysfunction. Sensory loss in the lower extremities follows a stocking distribution, and it has been noted that temperature and pain sensations are impaired earlier than proprioception. By the time sensory loss has progressed to the level of the knees, the hands usually become involved by a sensory neuropathy with a glove distribution. Motor loss develops later and frequently results in footdrop, wristdrop, and difficulty in hand function. Trophic ulcers on the lower extremities are common and, before the advent of antibiotics, were a frequent cause of infection and death. Orthostatic hypotension is common and has profound significance in patients with cardiac amyloid. Gastrointestinal symptoms are due mainly to nerve dysfunction with affected individuals having constipation alternating with diarrhea. Delayed gastric emptying may lead to distension of the organ and poor appetite. Cachexia is a frequent feature and may be a significant factor in mortality.
Pattern of sensory loss in familial amyloid polyneuropathy type I.
Visual involvement has been known to occur in the Portuguese syndrome but is much more frequently seen in Swedish kindreds and in the Indiana/Swiss amyloidosis (FAP II). Amyloid within the vitreous humor of the eye interferes with vision, but this can usually be corrected, at least temporarily, by surgical removal of the deposits (Fig. 209-12). The scalloped pupil deformity is another eye manifestation that has been described both in Portuguese and Swedish kindreds with FAP I, and is probably due to involvement of ciliary nerves. Autonomic neuropathy may cause urinary retention severe enough to require diversionary procedures to prevent renal damage. Hypohidrosis has also been seen.
Clinical features of the hereditary amyloidoses. A, Cardiomegaly in Ser84 amyloidosis. B, Technetium pyrophosphate uptake in cardiac amyloidosis. C, Gastric distension and dilated small bowel in Ala60 amyloidosis. D, Neurogenic ulcer and calcaneal osteomyelitis in Met30 amyloidosis. E, Two-dimensional echocardiography in Ser84 amyloidosis showing thickening intraventricular septum (IVS), left ventricular wall (PW), aortic (AOV), and mitral valves (MV), plus dilated left atrium (LA). F, Typical neuropathy of Met30 amyloidosis. This patient has neuropathic arthropathy (Charcot knee). G, Lattice corneal dystrophy of Finnish amyloidosis. H, Scalloped pupil in Met30 amyloidosis. I, Vitreous deposits in Ser84 amyloidosis.
Other clinical manifestations of hereditary amyloidosis depend on which organ systems are involved. FAP I patients (Portuguese, Swedish, Japanese) may have renal amyloid with significant protein loss and subsequent renal insufficiency. In these patients, dialysis may prolong life, but subsequent involvement of other organs is not prevented. The Indiana/Swiss kindred (FAP II), the Appalachian kindred, and several of the more recently described kindreds have severe cardiomyopathy, which is usually the cause of death. Cardiac conduction disturbances occur early and frequently require artificial pacing. The subsequent clinical picture is one of restrictive cardiomyopathy with low-output heart failure. Cardiomyopathy without peripheral neuropathy is the main feature of the amyloidosis described by Frederiksen et al., in Denmark.157
A number of transthyretin variants have been identified in the amyloid fibrils or plasma of patients with hereditary amyloidosis (Table 209-2). While the distribution of the amino acid substitutions gives no obvious clue to fibrillogenesis, all involve single amino acid substitutions that result from single nucleotide mutations in coding regions except for one which is the deletion of a codon (V122Δ).158 The substitutions range in location from amino acid residue 10 (Cys10Arg) to residue 122 (Val122Ile) of TTR, with 27 mutations in exon 2, 32 mutations in exon 3, and 14 mutations in exon 4. No mutation in exon 1 (coding amino acids 1 through 3) has yet been discovered. These findings provide a biochemical basis for classifying the transthyretin amyloidoses and show that, although the old classification based on the clinical syndrome and ethnic origin is basically sound, there is a great deal of overlap among the syndromes. Identification of nonsymptomatic carriers of variant transthyretin genes in many of the kindreds has widened the recognized time span of clinical onset for each syndrome. The following transthyretin variants have been identified in families with hereditary amyloidosis. The clinical, geographic, and ethnic parameters that are relatively unique to each familial syndrome are emphasized to aid the clinician in recognizing and diagnosing the disease. A few additional transthyretin variants have been identified (Table 209-2), but in these, insufficient clinical data have been reported.
Table 209-2: Transthyretin Amyloidoses |Favorite Table|Download (.pdf) Table 209-2: Transthyretin Amyloidoses
|Mutation ||Clinical Features* ||Geographic Kindreds |
|Cys10Arg ||Heart, Eye, PN ||United States (PA) |
|Leu12Pro ||LM ||United Kingdom |
|Asp18Glu ||PN ||South America |
|Asp18Gly ||LM ||Hungary |
|Val20Ile ||Heart, CTS ||Germany, United States |
|Ser23Asn ||Heart, PN, Eye ||United States |
|Pro24Ser ||Heart, CTS, PN ||United States |
|Val30Met ||PN, AN, Eye, LM ||Portugal, Japan, Sweden, United States (FAP I) |
|Val30Ala ||Heart, AN ||United States |
|Val30Leu ||PN, Heart ||Japan |
|Val30Gly ||LM, Eye ||United States |
|Phe33Ile ||PN, Eye ||Israel |
|Phe33Leu ||PN, Heart ||United States |
|Phe33Val ||PN ||United Kingdom, Japan |
|Arg34Thr ||PN, Heart ||Italy |
|Lys35Asn ||PN, AN, Heart ||France |
|Ala36Pro ||Eye, CTS ||United States |
|Asp38Ala ||PN, Heart ||Japan |
|Glu42Gly ||PN, AN, Heart ||Japan, United States, Russia |
|Glu42Asp ||Heart ||France |
|Phe44Ser ||PN, AN, Heart ||United States |
|Ala45Asp ||Heart, PN ||United States |
|Ala45Ser ||Heart ||Sweden |
|Ala45Thr ||Heart ||United States |
|Gly47Arg ||PN, AN ||Japan |
|Gly47Ala ||Heart, AN ||Italy, Germany |
|Gly47Val ||CTS, PN, AN, Heart ||Sri Lanka |
|Thr49Ala ||Heart, CTS ||France, Italy |
|Thr49Ile ||PN, Heart ||Japan |
|Ser50Arg ||AN, PN ||Japan, French/Italian |
|Ser50Ile ||Heart, PN, AN ||Japan |
|Glu51Gly ||Heart ||United States |
|Ser52Pro ||PN, AN, Heart, Kidney ||England |
|Gly53Glu ||LM, Heart ||Basque |
|Glu54Gly ||PN, AN, Eye ||England |
|Leu55Arg ||LM ||Germany |
|Leu55Pro ||Heart, AN, Eye ||United States, Taiwan |
|His56Arg ||Heart ||United States |
|Leu58His ||CTS, Heart ||United States (MD) (FAP II) |
|Leu58Arg ||CTS, AN, Eye ||Japan |
|Thr59Lys ||Heart, PN, AN ||Italy |
|Thr60Ala ||Heart, CTS ||United States (Appalachian) |
|Glu61Lys ||PN ||Japan |
|Phe64Leu ||PN, CTS, Heart ||United States, Italy |
|Phe64Ser ||LM, PN, Eye ||Canada, England |
|Ile68Leu ||Heart ||Germany |
|Tyr69His ||Eye ||United States |
|Lys70Asn ||Eye, CTS, PN ||United States |
|Val71Ala ||PN, Eye, CTS ||France, Spain |
|Ile73Val ||PN, AN ||Bangladesh |
|Ser77Phe || ||France |
|Ser77Tyr ||Kidney ||United States (IL, TX), France |
|Ile84Ser ||Heart, CTS, Eye, LM ||United States (IN), Hungary (FAP II) |
|Ile84Asn ||Heart, Eye ||United States |
|Ile84Thr || ||Germany, United Kingdom |
|Glu89Gln ||PN, Heart ||Italy |
|Glu89Lys ||PN, Heart ||United States |
|Ala91Ser ||PN, CTS, Heart ||France |
|Ala97Gly ||Heart, PN ||Japan |
|Ala97Ser ||PN, Heart ||Taiwan |
|Ile107Val ||Heart, CTS, PN ||United States |
|Ala109Ser || ||Japan |
|Leu111Met ||Heart ||Denmark |
|Ser112Ile ||PN, Heart ||Italy |
|Tyr114Cys ||PN, AN, Eye, LM ||Japan |
|Tyr114His ||CTS ||Japan |
|Tyr116Cys || ||France |
|Tyr116Ser || ||France |
|Val122Ile ||Heart ||United States |
|?Val122 ||Heart, PN ||United States (Ecuador) |
|Val122Ala ||Heart, Eye, PN ||United States |
This type of systemic amyloidosis presents as a peripheral neuropathy in the sixth and seventh decades of life. The only kindred that has been described is located in Pennsylvania with ancestors of Hungarian origin.159 No evidence for the mutation in Hungary has been found to date. In three cousins who died with this syndrome and who were studied in detail, severe cardiomyopathy and bowel dysfunction were the major factors leading to death between ages 64 and 70. This particular variant transthyretin has added importance for two reasons: (a) The mutation is the most N-terminal of all the amyloid associated mutations and is at the boundary of the less organized structure (amino acid residues 1 to 9) and highly ordered structure of the remainder of the transthyretin molecule.132 (b) Arginine 10 replaces the only cysteine in the transthyretin molecule. This may be significant in terms of the possible involvement of disulfide linkage in amyloid fibrillogenesis.
Subarachnoid hemorrhage at age 37 associated with leptomeningeal amyloid deposition was the presenting clinical picture in the first subject found to have this mutation. A similar clinical phenotype with subarachnoid hemorrhage has been reported with other transthyretin variants including Asp18Gly, Val30Gly, Phe64Ser, and Val122Δ.
This mutation was found in a 49-year-old subject from South America who had typical FAP.
A single Hungarian family has been described with this transthyretin variant. The clinical picture included memory loss, ataxia, hearing loss, spastic paraparesis, hallucinations, and urinary retention.160 The mutation A to G in the second position of codon 18 abolishes an XbaI restriction endonuclease site.161
This mutation was first described in a German family, the index case was a 60-year-old man with severe cardiomyopathy and mild peripheral neuropathy.162 It was also found in a 50-year-old man in the United States who received cardiac transplant for amyloid cardiomyopathy.163
Severe cardiomyopathy in a man in his thirties was found to be associated with this variant transthyretin.
Transthyretin Pro24Ser was discovered in a family with relatively late-onset amyloidosis.164 The propositus, who was born in Kentucky, developed carpal tunnel syndrome at age 50, severe diarrhea at age 65, and died at age 70. Three brothers died of cardiac disease, and in one, cardiac amyloidosis was documented at postmortem.
The substitution of serine for proline, the result of a C→T transition in the first position of codon 24, does not give a new restriction site, so a PCR-induced mutation-restriction analysis (PCR-IMRA) (see “Detection of Gene Carriers in Hereditary Amyloidosis” below) has been used to detect the carriers of this allele.
The most common type of hereditary amyloidosis thus far reported is characterized by a substitution of methionine for valine at position 30 of the transthyretin molecule. This variant transthyretin has been found in many kindreds in Portugal and Japan, and also in American kindreds of Swedish, English, and Greek origin.25,143,148,165-167 It has also been identified in Turkey, Majorca, Brazil, France, and England. While the largest numbers of patients and families have been identified in northern Portugal, the V30M allele has its highest prevalence in isolated communities in northern Sweden, where as much as 3 to 5 percent of the population may be heterozygous for the trait.168 A number of patients homozygous for the V30M allele have been identified in Sweden169 and in Turkey.170 The onset of clinical amyloidosis and progression of the disease in these homozygous individuals does not appear to be different from that of their heterozygous kin. Clinically, most of these kindreds have been classified as FAP I with neuropathy starting in the lower extremities. Varying degrees of renal and cardiac involvement have been reported, but autonomic and gastrointestinal symptoms are present in most patients. Vitreous deposits of amyloid have been reported, as has the scalloped pupil deformity.7 In particular, vitreous involvement appears to be much more common in the Swedish families than in the Portuguese families. Another interesting difference between Portuguese families and Swedish families with this same V30M mutation is the time of onset of disease. In Portugal, the mean age of onset is in the early thirties, with death often occurring by age 40. In Sweden, the mean age of onset of clinical disease is in the late fifties, and patients often live to the eighth decade. Mental functioning is generally not affected, but amyloid may be present in blood vessels of the central nervous system and in the leptomeninges.171 There is evidence that the high prevalence and worldwide distribution of the V30M transthyretin mutation is in some part due to multiple mutational events. The V30M mutation was found in Japan in association with three distinct haplotypes.172 One of these haplotypes is the same as the haplotype found in Portuguese V30M patients and Swedish V30M patients, suggesting that the gene has been spread from a common focus. The association of the V30M mutation with other haplotypes, however, suggests that separate mutation events may have occurred in Japan, and at least one V30M kindred of English origin in the United States does not share the Portugese-Swedish haplotype.173 The idea that multiple mutational events have generated the V30M transthyretin is supported by the fact that this position is one of the mutation hot spots in the TTR coding region, where the CpG dinucleotide sequence can be altered by deamidation of a methylated cytosine.
Substitution of alanine for valine at position 30 has been reported in association with systemic amyloidosis in one family.174 The disease had a relatively early onset in the twenties, with death in 4 to 6 years. Clinical manifestations include autonomic neuropathy with orthostasis and gastric atony, but only mild sensory neuropathy of the FAP I variety. No eye or renal involvement was clinically noted. Amyloid fibrils containing transthyretin were isolated from the heart of one individual. The T→C mutation in the second position of codon 30 gives a new CfoI restriction site in exon 2.
A third mutation at position 30 (Val30Leu) was discovered in a 53-year-old Japanese woman who presented with weight loss and diarrhea at age 51.175,176 Sensory neuropathy was present in the lower extremities and sural nerve biopsy revealed deposits of amyloid which stained positively with antihuman transthyretin antibody. No vitreous opacities were reported, and there was no family history suggestive of FAP. The G→C transition in the third base of codon 30 results in a novel Cfr13I site, which can be used for identification of this mutation.
This mutation was first identified in an American of French ancestry with vitreous opacities. It has also been found in the Ohio kindred of German origin which was reported as oculoleptomeningeal amyloidosis.177,178 The syndrome had minor systemic amyloid and peripheral neuropathy, but was characterized by vitreous opacities and extensive leptomeningeal amyloid deposition. Dementia and ataxia are a part of the syndrome.
This type of amyloidosis was originally called “Jewish FAP” because the only individual described with the disease was a Jewish man who was born in Poland and immigrated to Israel. The disease manifested as type I peripheral neuropathy, diarrhea, and impotence. Vitreous opacities were described between ages 25 and 30.179 Autopsy revealed amyloid in all major organs, particularly the thyroid, kidney, spleen, and nerves. The original studies of amyloid isolated from the thyroid showed that a significant proportion of the transthyretin molecules had been cleaved between amino acid positions 48 and 49, and there was evidence for a substitution of glycine for threonine at position 49.180 Subsequently, however, amyloid subunit protein isolated from splenic tissue showed an isoleucine substituted for phenylalanine at position 33.181 This substitution was verified by DNA sequence studies, which failed to show any mutation in codon 49. Incidentally, the affected individual in this kindred was found to also have the TTR mutation that gives serine at position 6, which has been described by others but not in association with amyloid formation. No other kindreds with the isoleucine 33 transthyretin amyloid have been described.
This mutation (Phe33Leu) was found in a middle-aged man of Polish and Lithuanian heritage who had lower limb neuropathy and cardiomyopathy.182 There was no previous family history of amyloidosis, and no other kindreds have been identified. The T→C mutation at the first base of codon 33 gives a new DdeI site in exon 2.
This mutation was reported for a single individual in the United Kingdom with typical FAP.
Three affected brothers from the Puglia area of Italy presented with polyneuropathy and restrictive cardiomyopathy after age 50.
One subject was found with this mutation producing typical amyloid polyneuropathy. This individual lived in France, but the country of origin was not determined.183
This mutation (Ala36Pro) has been described in two kindreds,184,185 an American family of Greek origin and a Jewish family in which members died between ages 36 and 65. The age of onset was 28 in one individual, and the symptoms included lower limb neuropathy, autonomic neuropathy, and vitreous opacities.
One kindred with glycine substituted for glutamic acid at transthyretin position 42 has been described in Japan (Toyama Prefecture).186 At least six members of the kindred were affected with FAP, which was manifested as lower-limb neuropathy, autonomic neuropathy, cardiomyopathy, and vitreous opacities. Onset of disease was between ages 35 and 41, and major morbidity was related to restrictive cardiomyopathy. This mutation was also found in an American Caucasian family with amyloidosis that also has the nonamyloidogenic H91N mutation and in one individual from Russia. The A→G mutation at the second position of codon 42 results in a new Cfr13I restriction site in exon 2.
This mutation was discovered in one individual, age 63, with amyloid cardiomyopathy. There was no family history of amyloidosis and no neuropathy was documented.
A single American of Irish descent has been described with peripheral neuropathy starting at age 26. When evaluated at age 32 he had severe headaches, autonomic neuropathy, hearing loss, and signs of amyloid cardiomyopathy. The serine for phenylalanine substitution is due to a thymine to cytosine mutation at the second base of codon 44 and can be detected by induced mutation restriction analysis.187
One individual with cardiomyopathy appearing at approximately age 50 was reported to be heterozygous for a threonine substitution (Ala45Thr) at position 45 of transthyretin.188 This individual was of Irish and Italian descent, and the family history suggested that the trait was from the Italian side of the family. Other studies of an American/Irish patient who died with restrictive cardiomyopathy showed the same mutation, but it is not known whether this single individual was a member of the previously reported kindred.
This mutation associated with peripheral neuropathy and cardiomyopathy was reported from the United States. The proband was heterozygous for both A45D and the nonamyloid G6S mutation. The proband's father, who died of amyloidosis, had only the A45D mutation.
The first evidence of a de novo mutation in transthyretin is represented by the arginine-for-glycine substitution at position 47.189 The proband of the family was a 38-year-old Japanese man who showed symptoms of autonomic neuropathy at age 29. Polyneuropathy was proved by sural nerve biopsy showing amyloid deposits that stained with antitransthyretin. No vitreous opacities were noted. DNA studies of both parents and two siblings failed to show the mutation in codon 45, thus suggesting that the C-for-G transversion may be a de novo mutation.
A family from Italy with cardiomyopathy and peripheral neuropathy in the fifth decade of life was found to have an alanine-for-glycine substitution at position 47.190 Although a PCR test based on mutation-induced restriction analysis to give a novel MspI site has been described, no other kindred with this mutation has yet been found.
This mutation was found in a Sri Lankan kindred with polyneuropathy.
This mutation was found in two distinct kindreds, one in France and one in Italy, both showing cardiomyopathy.191,192 The Italian kindred was reported to have vitreous opacities, which was not a feature in the French kindred. The French kindred, first reported in 1983, showed onset of polyneuropathy and carpal tunnel syndrome between ages 35 and 40, with subsequent development of restrictive cardiomyopathy.193 Clinical onset of disease was at a similar age in the Italian kindred, with polyneuropathy occurring in the fifth decade of life.
The proband in this Japanese kindred was 63 years old when she developed painful paresthesias in all extremities. A grandmother had similar neuropathy and a brother died of cardiac amyloidosis. The mutation is a C→T transition at the second base of codon 49. Original detection was by electrospray ionization mass spectrometry (ESI-MS), which revealed a 12-dalton shift in molecular mass of plasma transthyretin.194
This mutation (Ser50Arg) was discovered in a Japanese family in which affected members presented with peripheral and autonomic neuropathy in their early forties. One man died of generalized wasting 6 years after the onset of polyneuropathy.195 The abnormal TTR was present in serum and cardiac amyloid deposits.196 The T→G transversion in the first position of codon 50 gives a new MvaI site. This mutation has also been found in a European family.183
A G→T tranversion in the second position of codon 50 of TTR exon 3 giving a Ser50Ile mutation was identified in a 56-year-old Japanese woman with a 7-year history of sensorimotor and autonomic neuropathy.197 Another report of this mutation emphasized cardiomyopathy as cause of death.198
This mutation was reported from the United Kingdom and is associated with peripheral neuropathy, autonomic neuropathy, cardiomyopathy, and renal amyloidosis.
Seven members of one kindred from West Virginia of Dutch and German descent showed early-onset, aggressive, systemic amyloidosis which caused peripheral neuropathy, autonomic neuropathy, and vitreous opacities.199 Death in most individuals was from restrictive cardiomyopathy, and autopsy revealed diffuse systemic amyloid deposits. The variant is due to a T→C transition in the second position of codon 55 of transthyretin, which gives a proline substitution for leucine. In the one kindred, multiple organ system involvement was noted by age 35, and all patients had died by age 38. Over four generations anticipation was suggested, with the youngest individual affected at age 19, but there is no molecular evidence to support anticipation. This mutation was also found in a Chinese family in Taiwan with early onset amyloidosis.200
Mahloudji et al. originally described a number of kindreds in Maryland with this form of amyloidosis.201 It was classified as FAP II because of onset with carpal tunnel syndrome. The disease, however, has varied manifestations, with frequent painful neuropathy and relatively slow progression. Onset may be as early as the forties, but many patients live into their seventies. Death is frequently caused by cardiomyopathy, but the syndrome is distinguished from the Indiana/Swiss (I84S) form of FAP II by a lack of vitreous opacities. A T→A transversion in the second position of codon 58 results in substitution of histidine for leucine.202 The L58H transthyretin gene has been detected in families throughout the United States.203 Recently, the mutation was found in a family with amyloid cardiomyopathy living in the region of Germany from which the American immigrants originated in the 1740s.204 Only one haplotype has been demonstrated in several families with this mutant transthyretin, suggesting a common origin. Recently, one individual homozygous for the L58H gene was shown to have a rapid course of generalized neuropathy with clinical presentation at age 46 and death 6 years later.205 This is unlike the V30M and V122I TTR variants, in which homozygous individuals do not seem to have more aggressive disease.
A single family was described in which a mother, age 62, and her son, age 39, had lower limb neuropathy, autonomic neuropathy, and carpal tunnel syndrome.206 The mother had vitreous opacities noted at age 53, and the son developed neuropathy as early as age 36. The mutation, a T→G change in the second position of codon 58, results in a new BhaI restriction site.
Cardiac amyloidosis was the major feature in an Italian family with disease onset between 49 and 64 years.207 The mutation is a cytosine to adenine transversion at the second base of codon 59.
This type of amyloidosis (also called Appalachian amyloidosis) was originally discovered in a large kindred from West Virginia in which the disease was traced to a couple having Irish, English, and German ancestry.208,209 Since then, the T60A transthyretin variant has been found in other U.S. families of Irish lineage, and the gene has now been reported in patients in Ireland. It is also the first mutation to be found in Australia, in a family also of Irish origin. One family of Welsh origin now in the United States has been found with this mutation. Sensorimotor neuropathy is not a prominent feature of this syndrome, although some patients have carpal tunnel syndrome. Most affected individuals have some degree of peripheral neuropathy in the lower extremities, but incapacitation is related more to bowel disease and resultant malnutrition. Sexual impotence is common. Many affected individuals die of cardiomyopathy, which usually starts after age 50 and may not begin until after age 60. The disease is progressive but may run a 10- to 20-year course. While most individuals have died in their sixties, some have been known to live past age 90. Combined heart and liver transplantation has been done in at least one individual with this disease with good outcome. Postmortem examinations have shown amyloid in nerves, heart, and thyroid (Figs. 209-13 and 209-14). Significant amyloid in liver, kidney, and spleen has not been seen. The original Appalachian kindred is very large and is dispersed throughout the United States. The gene has also been detected in a large kindred in the northeastern United States.210 The T60A mutation is the result of an A→G transition at the first position of codon 60 and results in a new PvuII restriction site in exon 3.
Section of peripheral nerve stained for transthyretin by the avidin-biotin peroxidase method. Amyloid deposits are found within the nerve structure, and the positive staining for transthyretin proves the diagnosis of hereditary amyloidosis. ×100.
Section of left ventricle stained immunohistochemically using antitransthyretin. Amyloid deposits displace myocardial fibrils and also form rings around the cardiac muscle bundles. ×100.
This mutation was reported in a 62-year-old Japanese individual with diarrhea and sensorimotor neuropathy.211
This mutation (Phe64Leu) was discovered in one individual with disease beginning at age 66 as a peripheral neuropathy involving both upper and lower extremities.212 Cardiomyopathy was present, but no eye involvement was noted. The patient was an American of Italian descent.
The principal feature associated with this mutation is amyloid angiopathy involving the meninges of the brain and spinal cord, retina, and peripheral nerves. Vitreous opacities were also present. Clinical features included migraine, periodic obtundation, psychosis, seizures, intracerebral hemorrhages, myelopathy, deafness, and peripheral neuropathy.213 The syndrome was originally discovered in a Canadian family of Italian origin, but was recently found in a family in England with vitreous opacities and peripheral neuropathy. A transition of T→C at the second position of codon 64 creates a new HinfI site, which can be used for PCR-based gene detection.214
A substitution of leucine for isoleucine at position 68 of transthyretin was described in a 61-year-old German individual with cardiomyopathy.215 The mutation, an A→T transversion in the first position of codon 68, was detected in the propositus' son, who was unaffected, but not in the propositus' mother. The propositus' father died at age 56 of an accident without symptoms of amyloidosis. While polyneuropathy was suggested by complaints of dysesthesia, neurologic examination did not reveal objective pathologic findings.
Only one family has been reported with this mutation (Tyr69His).216 The proband noted symptoms of vitreous opacities at age 59, and amyloidosis was proved by pathologic examination of a vitrectomy specimen removed at age 62. The proband had symptoms of carpal tunnel syndrome and gastrointestinal complaints suggesting autonomic nervous system involvement. No peripheral neuropathy was noted, however. An older sibling also had vitreous opacities but died of a brain hemorrhage at age 62. The Y69H allele is the result of a T→C mutation in the first position of codon 69.
A family from New Jersey of German ancestry was found to have amyloidosis associated with a substitution of asparagine for lysine at position 70 of transthyretin.217 This is due to an A→C transversion at the third base of codon 70. This syndrome usually presents as carpal tunnel syndrome as early as in the thirties. One individual died of renal insufficiency, but nodular glomerulosclerosis characteristic of Kimmelstiel-Wilson disease was found instead of amyloid. Amyloid vitreous opacities were a common finding in this syndrome.
Val71Ala was first discovered in a family from northern France in which the proband developed carpal tunnel syndrome at age 35 and subsequently had lower limb neuropathy at age 42.218 The proband's father had paresthesias and diarrhea starting at age 40 and subsequently developed vitreous opacities. The V71A mutation, which is due to a C→T transition, in the second position of codon 71, has also been found in an individual in Spain.
This mutation was associated with FAP starting at age 50 years in multiple members of a Bangladeshi family with amyloid deposition proven in peripheral nerve. The A→G transition in the first position of codon 73 creates a new AccI restriction enzyme site.219
Amyloidosis associated with the tyrosine 77 transthyretin variant was originally described in a family of German extraction from Illinois.220 The clinical syndrome shows a lower limb neuropathy and diarrhea starting about age 50. While kidney failure has been a major cause of death, cardiomyopathy has also been noted in individuals with this mutation. This transthyretin variant has now been found with the same haplotype in several families in the United States, including a large kindred in Texas.221 A family from northern France, however, has the S77Y transthyretin with a different haplotype, suggesting a separate mutational event.222 The mutation, a C→T transition at the second position of codon 77, gives a new SspI restriction site.
Although the Indiana/Swiss kindred with amyloidosis was originally reported by Falls et al. in 1955,223 Rukavina's description of the kindred in 1956 caused his name to be used in identifying the syndrome, which, because of presentation with carpal tunnel syndrome, was designated FAP II to distinguish it from the FAP I peripheral neuropathy syndrome.224 Carpal tunnel syndrome occurs as early as the third decade of life, whereas infiltrative peripheral neuropathy tends to occur later in the course and can affect all extremities. Vitreous opacities are seen in essentially all affected individuals, and cardiomyopathy is the usual cause of death. Most patients die in their mid-fifties or sixties, although some individuals have reached age 80 with the help of artificial cardiac pacing. Sexual impotence is common in men, and bowel dysfunction with diarrhea and malabsorption is also common.225
The I84S mutation is the result of a T→G transversion in the second position of codon 84. This gives a new AluI restriction site, which can be used for DNA testing.226 Gene carriers in this kindred, both affected and presymptomatic, have significantly reduced plasma RBP concentrations. This finding agrees with structure data that show that this area of the molecule around residue 84 is involved in the interaction with RBP.136,137,227 The depression in the serum RBP level is such that heterozygotes can usually be identified by this measurement alone. Recently a second kindred with the I84S transthyretin gene was found in Hungary; this family, which also has vitreous and cardiac amyloid, may be related to the original Swiss/German families.228
A second mutation in transthyretin position 84 (Ile84Asn) is due to a T→G transversion in the second position of codon 84.229 It was reported in an individual who developed vitreous opacities at age 62. There was no family history of amyloidosis in this American family of Italian descent, although the proband's father died suddenly at age 62. Carpal tunnel syndrome developing after age 70 and mild cardiomyopathy were present in the proband. Plasma RBP concentration was found to be low as with the I84S mutation.135
A 60-year-old German woman with cardiomyopathy and peripheral neuropathy had this mutation, a T→C transition at the second base of codon 84.
The substitution of glutamine for glutamic acid at position 89 of transthyretin was discovered in a Sicilian family with carpal tunnel syndrome, cardiomyopathy, and neuropathy presenting in the fifth decade of life.191 This is the result of a G→C transversion in the first position of codon 89.
Peripheral neuropathy and cardiomyopathy after age 55 years characterized this disease in an American family. The mutation is a G→A transition at the first position of codon 89.230
This mutation was associated with peripheral neuropathy, carpal tunnel syndrome, and cardiomyopathy in a French family. The index case was 72 years old at presentation. The G→T transversion at the first base of codon 91 ablates a SphI restriction-enzyme site.231
This mutation in a Japanese kindred was associated with cardiomyopathy and peripheral neuropathy, but well-preserved autonomic function. Age of onset of clinical disease was 52 years with slow progression of disease.232
A 57-year-old man of English/German descent developed carpal tunnel syndrome at age 57 and, subsequently, generalized peripheral neuropathy at age 65.233 Amyloid deposition was identified on muscle biopsy. There was no family history of amyloidosis. A TTR mutation, A→G in the first position of codon 107, predicts a valine-for-isoleucine substitution.
This mutation was discovered in a 75-year-old Japanese woman with peripheral neuropathy. Sural nerve biopsy confirmed amyloid deposition.234 The G→T transversion at the first position of codon 109 abolishes a Fnu4H1 restriction enzyme site. It is of interest that the two other reported mutations at residue 109 are associated with euthyroid hyperthyroxinemia, but not with amyloidosis.145
In 1962, Frederiksen et al. described a kindred in Denmark with amyloid cardiomyopathy.157,235 No neuropathy was detected either at that time or on subsequent reexamination of the kindred. The clinical findings are those of restrictive cardiomyopathy. DNA sequencing showed a C→A transversion in the first position of codon 111, with the substitution of methionine for leucine.236 A recent analysis of sera obtained at the time of the original report has detected the mutant transthyretin in all affected individuals.237 No other kindreds have been discovered with this particular mutation, which is remarkable for its restriction of amyloid pathology to the heart.
This mutation was reported from Italy. The index case was 44 years old at presentation with cardiomyopathy, peripheral neuropathy, and chronic renal failure. Several family members had disease onset at this relatively early age. The mutation is a G→T transversion at the second position of codon 112.
Members of a kindred from Nagasaki prefecture in Japan were found to have systemic amyloidosis associated with a cysteine-for-tyrosine replacement at codon 114.238 This is the result of an A→G change in the second position of codon 114.239 The syndrome was manifest at age 30, with lower-limb neuropathy, autonomic neuropathy, and subsequent development of vitreous opacities. Heart failure was the most common cause of death.
This mutation was found in a Japanese kindred in Niigata prefecture with carpal tunnel syndrome, but without other features of amyloidosis.240
A 75-year-old French man with peripheral neuropathy and carpal tunnel syndrome had amyloidosis proven by sural nerve biopsy.231 The mutation, an A→C transversion at the second position of codon 116 creates a new Ear1 restriction-enzyme site. While there was no family history of amyloidosis, a daughter and a 70-year-old sister also had the mutation.
The Val122Ile mutation was discovered in an individual with cardiomyopathy but no family history of amyloidosis.241 It was first believed to explain some cases of senile cardiac amyloidosis. It is particularly interesting because the first two individuals reported with this mutation were from separate families, and both were homozygous for V122I transthyretin.242,243 Subsequently, other individuals have been discovered with cardiac amyloidosis who were heterozygous for V122I transthyretin.244 All affected individuals so far were elderly, presenting after age 60 with cardiomyopathy, and nearly all were African-Americans. The mutation, a G→A transition in the first position of codon 122, was present in approximately 4 percent of selected African-American cohorts and may be the cause of heart failure in a significant portion of the elderly in this population.245 Peripheral neuropathy has been reported, but is a minor clinical manifestation of this syndrome. Because transthyretin amyloidosis is an autosomal dominant trait, the high allele frequency makes this one of the most important genetic mutations in the United States. Unfortunately, the clinical disease in this population is frequently not diagnosed and, therefore, the affected individual receives less than optimal therapy. Recently, the mutation was found in populations of the west coast of Africa and in South Africa.
This is the first and only deletion mutation to be discovered for transthyretin. It is associated with peripheral and autonomic neuropathy and cardiomyopathy starting after age 60 years.158 The proband immigrated to the United States from Ecuador. DNA-sequencing gels of exon 4 PCR products reveal multiple bands due to the trinucleotide deletion.
This mutation was discovered in a 47-year-old American of Welsh and English descent who presented with cardiomyopathy.246 The T→C transition at the second position of codon 122 results in the loss of a MaeIII restriction enzyme site.
Senile Systemic Amyloidosis.
In addition to the characterized cases of senile cardiac amyloidosis, a number of postmortem studies show a high incidence of amyloid deposits in individuals dying after age 80.247 These deposits are often in the heart, but varying degrees of systemic involvement have also been noted.248,249
The term senile systemic amyloidosis has been used for these cases, as well as for those previously labeled senile cardiac amyloidosis.250 Immunohistochemical studies show that a number of these cases involve transthyretin amyloid, although some studies fail to show staining with antitransthyretin antisera.251 DNA-sequencing studies of some individuals with transthyretin cardiomyopathy without a family history of this disease failed to show mutations in the coding regions of the TTR gene.252 This finding suggests that normal transthyretin may, in some situations, produce amyloid fibrils without the presence of a mutation.
Transthyretin Variants not Associated with Amyloidosis.
A number of variants of transthyretin have been reported in individuals and families without evidence of systemic amyloidosis. These have been identified either by an association with altered thyroxine binding or by an abnormal pattern on protein electrophoresis. Although routine serum electrophoresis does not identify variant forms of transthyretin, both two-dimensional polyacrylamide gel electrophoresis and a system called “hybrid isoelectric focusing” have successfully discriminated several variants from normal transthyretin.253 In addition, advances in mass spectrometry have made detection of variant forms of transthyretin possible and may lead to discovery of more nonpathogenic variants of this plasma protein. A variant transthyretin with serine substituted for glycine at position 6 (G6S) was discovered in a family with hyperthyroxinemia.254,255 Studies suggest that an abnormal albumin in this kindred may cause increased thyroxine binding, giving a euthyroid state; and in vitro thyroxine-binding studies on a recombinantly produced G6S variant TTR failed to show increased thyroxine binding for this variant.256 G6S transthyretin may be a relatively common polymorphism having been reported in 12 percent of Caucasians. Amino acid substitutions at position 109 of transthyretin have also been identified in families with euthyroid hyperthyroxinemia. Ala109Thr (A109T) is the most thoroughly studied, with a fairly large kindred showing increased thyroxine binding but a euthyroid state.257 Thyroxine-binding studies of recombinant A109T TTR demonstrate increased affinity for T4,256 and a structural basis for this increased affinity was demonstrated by solution of the x-ray structure at 1.7Å.258 A valine substitution at position 109 has also been described in an individual with hyperthyroxinemia. Transthyretin Met119 was discovered by two-dimensional polyacrylamide gel electrophoresis in a family without any evidence of hyperthyroxinemia.146 This TTR variant may be relatively common in the general population, but has not been associated with amyloid deposition. Transthyretin T119M, like G6S and V30M, may be the result of a mutational hot spot, where deamination of a methylated cytosine at a CpG site would lead to this mutation. A transthyretin variant with histidine substituted for aspartic acid at position 74 (D74H) was discovered in individuals without evidence of amyloidosis;259 an asparagine for histidine at position 91 (H91N) and arginine substitution for proline at position 102 (P102R) have also been described.260 The number of known amyloid-producing variants of transthyretin far exceeds the number of nonamyloid variants. However, no concerted effort of population screening at the DNA level has been made to discover other clinically silent variants of this protein. With such a large number of amyloid-associated variants, it would appear that the propensity for amyloid fibril formation is significantly enhanced by most perturbations in primary structure of this heavily β-structured protein.
The pathogenesis of transthyretin amyloidosis is not well understood; although it is obvious that certain factors such as the extensive β-conformation of the protein, its inherent structural stability, and resistance to proteolysis must play important roles in amyloid fibril formation. The discovery of single amino acid substitution variants of transthyretin led to the hypothesis that changes in the structure of the protein in some way lead to aggregation of the subunit protein molecules to form fibrils. However, determination of the tertiary structure of a number of amyloidogenic, as well as nonamyloidogenic, transthyretin variants has failed to show common factors that would predict the transition of a soluble plasma protein to insoluble amyloid fibrils. The intramolecular position and type of amino acid substitution in transthyretin are not obvious factors in pathogenesis. Mutations from neutral to charged residues, from charged to neutral residues, from hydrophobic to hydrophilic, or hydrophilic to hydrophobic, have all been discovered to be associated with amyloid formation. The mutations are distributed over most of the length of the transthyretin molecule with only the N- and C-terminal segments not having mutations associated with amyloidosis. Even so, most speculation on transthyretin amyloid fibril formation is centered on hypothesized changes in tertiary structure caused by amino acid substitutions. One hypothesis is that under acidic conditions transthyretin is converted to a conformational intermediate that then self-associates to give fibrils.261 Another hypothesis is that amino acid substitutions cause changes in the edge strands (residues 45 to 58) of the two β-sheets that form the structural framework of the TTR molecule and this leads to molecular self-assembly giving growth of intermolecular β-sheet structures.262 Another possible mechanism is that, rather than changes in tertiary structure that lead to aggregation, amino acid substitutions may alter metabolism of the transthyretin molecule so the concentration or conformation of a proteolytic intermediate may be changed from the norm, and this may affect a pathway that leads to fibril formation. That normal transthyretin may generate amyloid fibrils favors this hypothesis. Some degree of intramolecular proteolysis in the process of amyloid formation is suggested by the fact that fragments of transthyretin representing amino acid residues 47 to 127, 49 to 127, and 52 to 127, are commonly found in amyloid fibrils extracted from tissues.
The liver predominantly synthesizes plasma transthyretin and this is the presumed source of substrate for amyloid deposits in the vascular tree, the heart, and the kidney. The liver and spleen, however, are rarely involved with significant amyloid deposition. The reasons for deposition in any particular organ are not readily apparent, but it is obvious that cardiac amyloid deposition is a predominant feature of many of the syndromes. The choroid plexus also synthesizes transthyretin and this may be the source for amyloid deposition in the leptomeninges. In addition, the retinal pigment epithelium synthesizes transthyretin, and this may be the source of amyloid in the vitreous of the eye. Recent reports of development of vitreous opacities in patients who have undergone orthotopic liver transplantation suggest that vitreous deposits are the result of intraocular synthesis and not hepatic synthesis. The predilection for amyloid deposition in peripheral nerves is not understood. Amyloid deposits may start as vascular deposits in vasa nervorum, but there is also evidence for significant deposition in dorsal root ganglia. This may explain the prominence of sensory neuropathy in many of the transthyretin amyloidoses.
Treatment of Transthyretin Amyloidosis.
The only specific therapy for transthyretin amyloidosis is liver transplantation.263,264 Replacement of the liver results in disappearance of variant transthyretin from the plasma, and presumably this would stop the synthesis of amyloid fibrils.265 While this appears to be the case in most individuals, a few reports of progression of vitreous opacities and cardiomyopathy have tended to dampen the enthusiasm for liver transplantation.
Progression in vitreous opacities may be related to synthesis of variant transthyretin by retinal pigment epithelium. On the other hand, progression of cardiac amyloid might be related to the fact that normal transthyretin may perpetuate amyloid fibril formation which was originally initiated by a variant transthyretin protein. To date, approximately 300 individuals have received orthotopic liver transplants and the 2-year survival is approximately 78 percent. Because other liver functions in these individuals are normal, the morbidity from surgery is less than for individuals who have liver transplants for primary liver disease. Most individuals have not shown objective evidence of improved neurologic function after transplantation; however, regeneration of nerve fibers documented by sural nerve biopsy was recently reported.266 While liver transplantation may represent a specific and essentially curative treatment for systemic amyloidosis, the cost of this procedure and present-day problems with organ procurement and tissue rejection preclude its general use and acceptance.
In addition to liver transplantation, there are nonspecific therapeutic measures that may significantly prolong the life of an individual with transthyretin amyloidosis. Renal dialysis may be used for patients who have severe nephropathy. Cardiac pacemakers have prolonged life for many individuals. Potent diuretics can significantly improve the quality of life for patients with restrictive cardiomyopathy, but frequently some degree of volume overload is necessary to maintain adequate cardiac filling and, therefore, tissue perfusion. Bowel involvement can be devastating to some individuals; the judicious use of antibiotics to reduce intestinal flora and of agents such as metoclopramide to stimulate gastric emptying has been helpful. Vitrectomy can restore vision to some patients with vitreous opacities, although all too often this is only temporary. Patients who have had a vitrectomy for amyloidosis should be observed carefully for development of secondary glaucoma, which can be painless and can cause irreversible retinal damage. Plasmapheresis has been tried in some individuals with transthyretin amyloidosis but, while anecdotal reports suggest some improvement in quality of life, no definite therapeutic advantage has been noted. Colchicine is commonly given because of the reports of its preventing amyloid in familial Mediterranean fever. There is no definite evidence that it prevents transthyretin amyloid fibril formation, but nevertheless it is frequently given in the hope that it might delay the onset or progression of amyloid formation particularly in presymptomatic carriers of mutant transthyretin genes. A very significant factor in the treatment of patients with transthyretin amyloidosis is genetic screening, which allows identification of subjects with this condition so that they can receive timely diagnosis and treatment.
Hereditary Amyloidosis not Associated with Transthyretin
Apolipoprotein a-I Amyloidosis (MIM 107680).
In 1969, Van Allen et al. described a kindred from Iowa of English, Irish, and Scottish descent with autosomal dominant amyloidosis causing the nephrotic syndrome and/or renal insufficiency.267 Individuals in their twenties have been shown to be affected, but others lived into their seventies. A striking incidence of peptic ulcer disease was seen in this syndrome. Lower-limb neuropathy is characteristic of this syndrome, which in the past was called “FAP III,” although a few reports have called it “FAP IV” (Table 209-3).
Table 209-3: Mutant Proteins (Other Than Transthyretin) Associated with Autosomal Dominant Systemic Amyloidosis |Favorite Table|Download (.pdf) Table 209-3: Mutant Proteins (Other Than Transthyretin) Associated with Autosomal Dominant Systemic Amyloidosis
|Protein ||Mutation ||Clinical Features ||Geographic Kindreds |
|Apolipoprotein Al ||Gly26Arg ||PN,* nephropathy ||United States |
| ||Leu60Arg ||Nephropathy ||England |
| ||Trp50Arg ||Nephropathy ||England |
| ||del60–71 insVal/Thr ||Hepatic ||Spain |
| ||del70–72 ||Nephropathy ||South Africa |
| ||Leu90Pro ||Cardiomyopathy, cutaneous ||France |
|Gelsolin ||Asp187Asn ||PN,* Lattice corneal dystrophy ||Finland, United States, Japan |
| ||Asp187Tyr ||PN* ||Denmark, Czech |
|Cystatin C ||Leu68Gln ||Cerebral hemorrhage ||Iceland |
|Fibrinogen ||Arg554Leu ||Nephropathy ||Mexico |
| ||Glu526Val ||Nephropathy ||United States |
| ||4904delG ||Nephropathy ||United States |
| ||4897delT ||Nephropathy ||France |
|Lysozyme ||lle56Thr ||Nephropathy, petechiae ||England |
| ||Asp67His ||Nephropathy ||England |
Amyloid fibrils isolated from tissues of a patient with this syndrome were found to contain a degradation product of a variant form of apolipoprotein A-I (GenBank NM_000039), with arginine replacing glycine at position 26 (G26R).31,268 While both normal and variant types of apolipoprotein A-I were demonstrated in the plasma of affected individuals, only the G26R variant arginine 26 apo A-I was found in amyloid fibril deposits. A second American kindred of Italian origin was subsequently identified with this mutation, and families in England have been described with and without neuropathy. The G26R substitution is the result of a G→C transversion in the first position of codon 26 in exon 2.268
A second apolipoprotein A-I mutation, Leu60Arg (L60R), was identified in an English family in which the propositus presented at age 24 with splenic and hepatic amyloidosis.269 Subsequently, this individual developed hypertension and thrombocytopenia. Other members of the kindred presented with renal amyloidosis, but no evidence of neuropathy. Chemical analysis of amyloid fibrils revealed apo A-I degradation peptides of 88, 92, and 93 residues, whereas the original mutated apo A-I amyloid protein showed no peptides beyond residue 83 of apo A-I. No normal apolipoprotein A-I was found in the L60R amyloid fibrils.
A substitution of tryptophan by arginine at position 50 (W50R) is associated with non-neuropathic amyloidosis in a Jewish kindred. The proband presented with hepatic and renal amyloidosis. Amyloid fibrils isolated from liver contained apo A-I peptides of 1 to 86, 1 to 92, and 1 to 93 residues.270 Two deletion mutants of apo A-I have been found in families with amyloidosis. The first has a deletion in exon 4 that results in the loss of residues 60 to 71 with insertion of two new residues Val-Thr.271 Hepatic amyloid is the main feature of this syndrome and death, usually by the sixth decade, is from liver failure. The only family identified so far is from Spain. Another apo A-I deletion mutant with loss of amino acid residues 70 to 72 (Glu Phe Trp) was discovered in a kindred in South Africa.272 Death is from renal failure, although liver and spleen may also be affected. A completely different clinical syndrome associated with an apo A-I variant was recently described. A substitution of proline for leucine at position 90 (L90P) results in extensive cutaneous amyloid deposition and subsequently restrictive cardiomyopathy.273 Affected individuals in a kindred from Southern France developed skin rash by age 50 and died of heart failure by the sixth or seventh decade of life. Amyloid fibrils isolated from cardiac tissue contained a peptide of the variant apo A-I representing residues 1 to 94 with the L90P variant. Amyloid fibrils from the skin, however, contained only the normal residues 1 to 88.274
Apolipoprotein A-I, like transthyretin, has been associated with amyloid deposits without evidence of a variant form of the protein. Amyloid deposits that are frequently found at postmortem in the intima of the aorta contain peptides of apo A-I.275 Unlike transthyretin, apo A-I has been found to be associated with amyloidosis in another species than humans. Pulmonary vascular deposits of amyloid in aging dogs contain N-terminal peptides of apo A-I.276
Gelsolin Amyloidosis (MIM 137350).
In 1969, Meretoja described familial amyloidosis with lattice corneal dystrophy, progressive cranial neuropathy, and skin changes with various internal symptoms.277-279 The first manifestation of the disease is a dystrophic change of the cornea due to amyloid deposition. Over several decades, thickening of the skin on the forehead and back occurs, and patients may develop facial paralysis caused by cranial neuropathies. Death related to renal and cardiac amyloid has been reported. While the largest occurrence of this type of amyloidosis is in Finland, there have been reports of patients in the United States,280-282 Denmark, and Canada. An amyloid subunit protein of 71 amino acid residues derived from plasma gelsolin was isolated from tissues of patients with this disease and shown to have an asparagine substituted for the aspartic acid at position 187 (D187N).32,33,283 This substitution is caused by a G→A transition,284,285 which has now been demonstrated in American families286 and in a Japanese kindred.287 So far, haplotype analysis has provided evidence for more than one mutational event leading to the various kindreds in Finland and Holland.288 Individuals homozygous for the D187N variant have demonstrated early onset of severe renal amyloidosis.289 Recently, a tyrosine-for-aspartate substitution at residue 187 (D187Y) was identified in kindreds from Denmark and Czechoslovakia, with syndromes similar to the amyloidosis described by Meretoja. The same mutation, a G→T transversion at the first position of codon 187, was demonstrated for both kindreds, but they had different haplotypes, suggesting separate mutational events.288 No other families with this mutation have been identified. Recently, other types of corneal dystrophies which link to chromosome 5q31 have been found to be caused by mutations in keratoepithelin.290,291 These diseases are not associated with systemic amyloid deposition and can be considered under localized amyloidosis.
Gelsolin is a calcium-binding protein that binds to and fragments actin filaments (GenBank NM000177).292 There are two forms of gelsolin encoded by a single gene and derived through alternative splicing. A cytoplasmic gelsolin binds actin monomers and may have an important role in the reorganization of the cytoskeleton during receptor-mediated signaling.293 Plasma gelsolin (93 kDa) also binds actin and presumably functions to clear actin from the plasma. The gelsolin gene is on chromosome 9 (9q32-q34) and spans approximately 70 kb.294 The genomic structure has been partially determined and the gene shown to contain at least 14 exons. The higher molecular weight of plasma gelsolin is due to a 25-amino-acid extension at the N-terminal of the protein and is the result of alternate splicing. In the human, the plasma concentration of gelsolin is approximately 220 mg/liter. Unlike transthyretin and apolipoprotein A-I, which are synthesized mainly by the liver, plasma gelsolin is derived in large part from muscle.295 Therefore, organ transplantation is not an option for treatment of gelsolin amyloidosis.
Fibrinogen-Associated Amyloidosis (MIM 134820).
Mutations in the fibrinogen Aα-chain gene have been identified in individuals with familial autosomal dominant amyloidosis.34 To date, two missense mutations and two single nucleotide deletion mutants have been found associated with amyloidosis. The disease in these families shares several features. First, it is relatively early in onset, often appearing in the patient's forties, but sometimes in the twenties or earlier. Second, the principal manifestation of the amyloidosis is nephropathy, often presenting with hypertension and proteinuria. Third, there is no peripheral neuropathy. All known amyloid associated mutations are in the protease-sensitive C-terminal region of fibrinogen Aα.
Fibrinogen is a major plasma protein that is involved in the final phase of blood coagulation. It is composed of two sets of three different polypeptide chains, α, β, and γ, which have molecular weights of 66,000, 52,000, and 46,500, respectively, and are the products of closely associated genes on chromosome 4 (see Chap. 171).296-298 Fibrinogen is converted to insoluble fibrin by the action of thrombin and factor VIIIa. A number of mutations in the fibrinogen Aα-chain have been described in individuals with dysfibrinogenemia (Chap. 171), but none has shown an association with amyloidosis.299 Most of these mutations are in the N-terminal end of the fibrinogen Aα-chain (GenBank NM_000508). The plasma concentration of fibrinogen is approximately 3 mg/ml, and it functions as a moderate acute-phase reactant. A substitution of leucine for arginine at residue 554 (R554L) of the fibrinogen Aα-chain was identified in amyloid fibril subunit protein isolated from kidney tissue of a Peruvian patient who died with renal amyloidosis.34 A sister and son also had biopsy-proven amyloidosis and died with renal failure, the sister at age 28 and the son at age 24. Genomic DNA sequencing revealed a G→T transversion at nucleotide position 4993 of the fibrinogen Aα-chain gene, corresponding to the second base of codon 554. This mutation was recently found in an African-American family and in a French family.300,301
Another fibrinogen Aα-chain variant with valine substituted for glutamic acid at position 526 (E526V) caused by a A→T mutation at nucleotide 1674 was discovered in two large, unrelated American kindreds with renal amyloidosis.302 The disease in both kindreds had typical autosomal dominant inheritance, and there was no history of either neuropathy or coagulopathy. In at least one case, postmortem examination found amyloid deposition in the spleen but not the heart. Typical pathology in all individuals, however, is dense amyloid deposition in renal glomeruli. Families with the E526V fibrinogen Aα-chain amyloidosis have been found in Canada and in Germany.303 Two single-nucleotide deletion mutations have been described in kindreds with autosomal dominant renal amyloidosis. The first is an American family with renal failure starting in middle age. This syndrome is due to a 4904delG mutation of the fibrinogen Aα-chain gene.304 This results in a frameshift and new C-terminal sequence for the Aα-chain, 23 residues before a premature stop codon occurs (Fig. 209-15). A second deletion mutant (4897delT) was found in a French kindred.305 This deletion leads to a similar aberrant peptide of 26 residues at the C-terminus of the Aα-chain. This last variant is of particular interest because it resulted in renal amyloidosis in one individual age 12 years and amyloid recurred in a renal graft 2 years after transplant.
The C-terminal portion of the fibrinogen Aα-chain amino acid and gene sequence showing the two missense mutations associated with amyloidosis (Glu526Val and Arg554Leu) and the abnormal peptide sequences resulting from single nucleotide deletions 4904delG* and 4897delT*.
Lysozyme-Associated Amyloidosis (MIM 153450).
Two mutations in human lysozyme (GenBank M19045) have been reported to be associated with non-neuropathic systemic amyloidosis.306 In one family, petechial skin rash from childhood and subsequent renal failure characterized the syndrome. A mutation at residue 56 of lysozyme with threonine replacing isoleucine (I56T) was found by amino acid sequencing of an amyloid fibril subunit protein isolated from renal tissue. The full-length variant lysozyme molecule was present in the amyloid deposits, and no normal lysozyme was found. The I56T change is caused by a single-base T→C transition in exon 2 of the lysozyme gene. An aspartic acid-to-histidine mutation at residue 67 (D67H) was found by DNA analysis of members of a second family with renal amyloidosis. This mutation is the result of a single-nucleotide change with a G→C transversion in the first base of codon 67. In both lysozyme mutations, the affected individuals were heterozygotes, consistent with an autosomal dominant form of amyloidosis.
Lysozyme is a bacteriolytic enzyme present in external secretions, polymorphonuclear leukocytes, and macrophages. Its biologic significance is not completely known, and polymorphic forms not associated with amyloidosis have not been described. Fibrillogenesis may be related to transition from α structure to β-conformation via unstable intermediates.306
Cystatin C Amyloidosis (MIM 105150).
In 1972, Gudmundsson et al. described a syndrome of premature strokes and intracranial hemorrhage in Icelandic families.307 The syndrome (hereditary cerebral hemorrhage with amyloid) usually occurred in the third or fourth decade of life and showed autosomal dominant inheritance. Neurologic symptoms varied, depending on the location and severity of hemorrhage and, while some individuals died abruptly, others suffered numerous nonfatal cerebral accidents over several years before death. Postmortem examinations showed amyloid primarily restricted to cerebral blood vessels; subsequent studies, however, report systemic deposits. Chemical analysis of this amyloid has shown a fibril subunit that is a degradation product of cystatin C (γ trace protein).308 The amyloid subunit lacked the first 10 residues of cystatin C and, in addition, a glutamine was found at position 58 (residue 68 of intact cystatin C) instead of the normal leucine (L68Q).309 DNA analysis has shown the clinical disease segregating with the L68Q substitution.310 Individuals affected with this disease show extremely low levels of cystatin C in the cerebrospinal fluid, which provides an alternative test for detection of carriers.311 Senile plaques containing amyloid of the type seen in Alzheimer disease are not a feature of the Icelandic amyloidosis.312
Cystatin C, a cysteine protease inhibitor, contains 120 amino acids in a single polypeptide chain (GenBank NM_000099). It is the product of a single-copy gene on chromosome 20. The gene, which covers approximately 7 kb, contains three exons and is expressed in many tissues, including kidney, liver, gut, pancreas, and heart.313
Visceral deposition of amyloid, including deposits in spleen, while not usually of clinical significance, indicates that this is a systemic form of amyloidosis. While there is no specific treatment for this form of leptomeningeal amyloidosis, it has been shown that aggregation of the variant cystatin C protein is accelerated by temperatures above 37°C and, therefore, fever may promote amyloid formation in carriers of the mutant gene.314
Hereditary Cerebral Hemorrhage with Amyloid (Dutch) (MIM 104760).
Several families with congophilic angiopathy of the cerebral vessels resulting in intracerebral hemorrhage have been described in Holland. Affected members of these families have neither the cystatin C mutation described in hereditary cerebral hemorrhage with amyloid type I (HCHWA-I) nor low spinal fluid concentrations of cystatin C. Instead, amyloid isolated from leptomeninges contains the β-peptide analogous to the fibril subunit found in Alzheimer plaques and vascular deposits.315 A glutamine substitution for glutamic acid at residue 693 (E693Q) of the 770-amino-acid form of β-amyloid precursor protein (β-APP) was found, and this mutation was corroborated at the DNA level.316 While senile dementia is not a feature of this syndrome, there have been reports of intracerebral β-amyloid deposits demonstrated by immunohistochemistry with specific antibodies. Recently, a mutation at codon 692 (Ala692Glu; A692E) of the β-APP gene, which is also associated with cerebral hemorrhage, has been described.317 Individuals in these families, which are also of Dutch origin, show an early-onset form of familial Alzheimer disease, as well as cerebral hemorrhage from congophilic angiopathy. Unlike cystatin C amyloidosis (HDHWA-I), the Dutch disease (HCHWA-D) appears to be a localized form of amyloidosis as are other syndromes associated with mutations in the Alzheimer β-PP protein.
Familial Mediterranean Fever (MIM 249100).
Familial Mediterranean fever (FMF) is the only syndrome in which systemic amyloidosis appears in a definite autosomal recessive pattern. Siegal first described FMF in 1945, using the name benign paroxysmal peritonitis.318 Other terms applied to this syndrome include familial paroxysmal polyserositis and periodic fever. Heller used the term familial Mediterranean fever and first noted the autosomal recessive inheritance.319 A high percentage of patients with FMF develop systemic amyloidosis with prominent renal involvement.
FMF is seen most frequently in individuals of Mediterranean origin.320,321 It is particularly prominent in Sephardic Jews and Armenians. The disease is characterized by periodic episodes of fever, which may be accompanied by signs of peritonitis, synovitis, pleuritis, or an erythematous rash. These attacks may occur within the first decade of life and usually persist throughout life. The clinical manifestations have wide variability, however, and some patients have only mild abdominal discomfort during attacks. Large joint effusions can be seen, but these usually resolve without residual effects.322 The pathologic mechanisms underlying these attacks are unknown, and biopsies of either peritoneum or pleura show nothing more than evidence of mild inflammation. The attacks are self-limiting and usually resolve after 2 or 3 days.
FMF is transmitted as a simple autosomal recessive trait, and linkage analysis has localized the FMF gene to the short arm of chromosome 16.323 The FMF gene frequency in Sephardic Jews has been calculated as 0.22.324,325 FMF-type illnesses have been described in other ethnic groups, however, and in some instances autosomal dominant inheritance with incomplete penetrance cannot be excluded. While systemic amyloidosis is common in patients with FMF, the relationship between the FMF and amyloidosis is not clear.326 The development of amyloidosis does not correlate well with numbers or degrees of febrile attacks, and indeed some members of FMF kindreds have been described with amyloidosis but without the febrile attacks.327 The incidence of amyloidosis in FMF patients of Armenian descent is much lower than in Sephardic Jews, supporting the hypothesis that FMF and amyloidosis are two separate traits with separate genetic bases. The recent characterization of the FMF gene (MEFV) and identification of mutations associated with the clinical syndrome have not answered the question of variable incidence of amyloidosis in different ethnic populations. Two research groups cloned the gene for FMF and named the postulated protein pyrin and marenostrin.328,329 Several missense mutations have been identified and segregate with the disease in large kindreds. The FMF gene (GenBank NM_000243) encodes a 3.7-kb transcript that is expressed in granulocytes. The predicted protein is a member of a family of nuclear factors homologous to the R052 autoantigen. Identified mutations in the C-terminal portion of the predicted 781-residue protein include M680I, M694V, M694I, and V726A. All were found in families with FMF and segregate with disease. While the M694V, which is most prevalent in North African Jews, has the greatest correlation with amyloidosis, it is still not clear whether the specific mutation modulates the development of amyloid. The expanding number of mutations (presently over a dozen) and the occurrence of compound heterozygotes also clouds this issue.
The amyloidosis of FMF typically has a predilection for renal involvement with nephrotic syndrome followed by azotemia. Many patients die by their early twenties. Pathologically, glomerular deposits of amyloid predominate. The spleen is commonly involved, and the thyroid may be heavily infiltrated. Vascular deposits throughout the body are common but rarely lead to organ dysfunction. Treatment with either chronic hemodialysis or peritoneal dialysis yields fair results and kidney transplantation is effective.330 Treatment with colchicine prevents the febrile attacks in most patients and is associated with a lack of progression of amyloidosis.331 This has led to treatment of all FMF patients with colchicine. In studies by Zemer et al., only patients who did not maintain this therapeutic regimen developed progressive renal amyloidosis.332
The amyloid fibrils of FMF contain protein AA, and on chemical grounds this amyloidosis is the reactive type.13,16 The serum SAA concentration usually increases during febrile attacks and returns to normal between attacks. Because SAA levels are elevated by attacks of inflammation, it would appear that the amyloidosis of FMF is indeed a reactive type not only chemically but clinically, and that at least two determining factors act in concert. Variables that may lead to the differences in expression of the amyloidosis include: (a) penetrance of the FMF genetic trait; (b) prevalence of an amyloidogenic SAA allele (on chromosome 11) in the population at risk; and (c) environmental, dietary, and metabolic factors that may modulate the expression of the SAA genes and degradation of their protein products.
Muckle-Wells Syndrome (MIM 191900).
In 1962, Muckle and Wells described a syndrome characterized by nerve deafness, fever, urticaria, malaise, and “augey” bouts (attacks of urticaria or angioedema-like symptoms).333 Nephrotic syndrome developed by middle age, and affected individuals died of renal insufficiency. Postmortem studies showed glomerular amyloidosis plus involvement of the adrenals and spleen. Families with similar syndromes have been described, including one family of Norwegian descent334 and one Irish family in which familial Hibernian fever was described.335 While the original description supports autosomal dominant inheritance, this syndrome is similar to FMF in that the amyloid contains protein AA.336 The gene for Muckle-Wells syndrome has been localized to chromosome 1q44;336a whereas the FMF gene ( MEFV ) is on chromosome 16. The gene for familial Hibernian fever has now been identified as the tumor necrosis factor alpha (TNFα) gene (chromosome 12), and several mutations are associated with the disease. It is likely that the familial fever syndromes represent an heterogeneous group of diseases with a common final pathway of clinical expression.
Miscellaneous Hereditary Amyloidosis Syndromes.
In 1932, Ostertag described a familial syndrome of renal amyloidosis (MIM 105200).10 More recently, Weiss and Page provided an excellent pathologic description of the nephropathy in another family.337 The main feature is renal amyloid without neuropathy and death resulting from azotemia. At autopsy the adrenals and spleen, as well as the kidneys, may be involved with amyloid. Possible precursor proteins associated with this type of amyloidosis include mutant forms of apolipoprotein A-I,268-274 and variants of plasma fibrinogen.34 The family originally described by Ostertag has so far not been found, and the family of Weiss and Page, while under study, has not yet revealed the secret of their amyloidosis.
Localized Hereditary Amyloidosis
Localized amyloidosis occurs in a number of syndromes. The first to be characterized chemically was the amyloid associated with medullary carcinoma of the thyroid (MIM 155240). This carcinoma occurs in both sporadic and autosomal dominant patterns and is frequently associated with other endocrinopathies, including pheochromocytomas.50,51 This syndrome has been designated “multiple endocrine” neoplasia type 2 (MEN2; MIM 171400; see Chap. 42).338 Chemically, the amyloid is composed of peptides derived from procalcitonin and is limited to the thyroid or tumor metastases.339
Cutaneous amyloidosis has been reported in families and may be characterized as lichenoid changes of the skin.340-343 Cutaneous amyloidosis appeared to be autosomal dominant (MIM 105250) in a family reported by Rajagopalan and Tay,53 but there have also been reports of X-linked disease (MIM 301220).344 Familial bullous cutaneous amyloid (MIM 204900) infiltration has also been reported. It is possible that some of the previously described familial cutaneous forms of amyloidosis are similar to the recently discovered apolipoprotein A-I amyloidosis.274
Isolated atrial amyloidosis is a localized form of amyloidosis that occurs with increasing prevalence in aging hearts,345 but is occasionally recognized in a familial pattern.346 Small deposits of amyloid along the sarcolemma of atrial muscle cells may be observed as early as age 40, and prevalence may reach 95 percent by the ninth decade of life.347 The hemodynamic significance of this form of amyloid is not clear, but in some families it may be associated with atrial standstill.346
Isolated atrial amyloid contains a 28-amino-acid residue C-terminal degradation product of atrial natriuretic peptide.348-350 This peptide is synthesized by cardiac myocytes and may be induced as a response to congestive heart failure. This suggests that the increasing prevalence of atrial amyloidosis with age may be associated with ventricular dysfunction.351 The familial atrial standstill syndrome, however, may show no heart failure and may be related to an unknown genetic factor.352
Clinically, perhaps the most important of the localized amyloidoses is Alzheimer disease, a progressive dementia characterized by accumulations of amyloid substance in the brain (see Chap. 234).54 Amyloid deposits (plaques) in cortical tissues are associated with neurofibrillary tangles and blood vessel deposits (congophilic angiopathy), which also stain histologically as amyloid. While only 10 to 20 percent of Alzheimer disease is clearly inherited, it is a late-onset disease, and many familial cases may not be recognized.353 The Alzheimer plaques and congophilic angiopathy deposits contain a subunit protein (amyloid β-protein or β-A4 protein) having a molecular weight of approximately 4000 and from 39 to 42 amino acid residues and representing an internal fragment of the C-terminal portion of an amyloid precursor protein (β-APP).36 β-APP is the product of a single gene on chromosome 21q and has at least three alternatively spliced transcripts, the largest encoding a protein of 770 amino acid residues.354-356 While most cases of Alzheimer disease are sporadic, definite autosomal dominant inheritance is seen in many kindreds, and, recently, point mutations in the β-APP gene localized to chromosome 21 that are associated with Alzheimer pathology in a small number of families were described. In particular, four different amino acid substitutions at codon 717 of β-APP were found to be associated with Alzheimer disease,357-359 and other amino acid substitutions in the β-amyloid peptide sequence were shown to be associated with either cerebral hemorrhage as in hereditary cerebral hemorrhage with amyloid type D (HCHWA-D) or dementia.316,317 A larger number of families with familial Alzheimer disease have mutations in the presenilin (presenilin 1 (PS-1)) gene on chromosome 14.360 To date, over 60 PS-1 mutations have been identified in families with Alzheimer disease. Two mutations in the presenilin 2 gene on chromosome 1 have been identified, one in the Volga-German families and one in Italian families.361,362 Several studies have reported evidence that mutations in β-APP and presenilin genes are associated with changes in β-APP protein metabolism and generation of increased amounts of the 1 to 42 amino acid residue Aβ-peptide.363,364
Gerstmann-Sträussler-Scheinker disease and familial forms of Creutzfeldt-Jakob disease have also been shown to be heterogeneous.365 Each is associated with several mutations in the prion protein, which is also implicated in the transmissible forms of Creutzfeldt-Jakob disease and Kuru in humans and Scrapie in sheep (see Chap. 224).366,367
Type 2 (adult-onset) diabetes mellitus was shown to be associated with hyalinized pancreatic islets of Langerhans as early as 1900.368 Subsequently, this hyalinized material was shown to meet the criteria of amyloid and, therefore, this is a form of localized amyloidosis. Little progress was made in understanding this form of amyloidosis until it was found to be associated with age-associated diabetes in cats, as well as humans and some nonhuman primates.369 Isolation of a unique 37-amino-acid peptide, first from an insulinoma and subsequently from diabetic islets, proved that this was a new type of amyloid protein.38,370 This peptide, which is called either islet amyloid polypeptide (IAPP) or amylin,371 is the product of a gene on the short arm of chromosome 12.372 It is synthesized predominantly in β-cells of the pancreas and is cosecreted with insulin, although in molar amounts 100 times less. Islet amyloid polypeptide has significant (43 to 46 percent) homology with calcitonin-gene-related peptides (CGRP) 1 and 2, which are neuropeptides encoded on chromosome 11.373
The functions of islet amyloid polypeptide in normal physiology are not known, although various effects on insulin secretion and function have been reported. The relation of islet amyloid polypeptide to the pathogenesis of diabetes also remains to be determined. The restriction of the islet amyloid deposits to certain species (humans, apes, and cats) and the association with glucose intolerance in these species suggests that it is of importance in diabetes. The idea that this form of amyloidosis represents a hereditary condition rests on its association with type 2 diabetes, which has obvious but unclear genetic features. So far, no polymorphisms in the coding regions of the islet amyloid polypeptide gene have been discovered to explain the development of this form of amyloid, but regulation of gene expression has been incompletely explored. Amyloid in the pancreatic islets of a South American rodent (Octodon degus) was shown to contain insulin instead of islet amyloid polypeptide as the fibril subunit protein.374
Other clinically recognized types of localized amyloidosis are associated with specific syndromes. Tumoral deposits of amyloid in the urinary tract are common and have been shown to contain immunoglobulin light chain protein.375 Ureteral obstruction or hemorrhage from the bladder may lead to clinical recognition of these deposits.376 Amyloid in the respiratory tract without systemic involvement has been frequently reported and has been shown to be of immunoglobulin origin.377 Amyloid deposits in senile articular cartilage may occur with or without association of calcium pyrophosphate deposition disease.378 It is possible that these deposits are related to the β2-microglobulin articular amyloid that is seen in chronic dialysis patients, but no studies have been reported on this topic. It is also possible that these deposits may be a reactive type as is the articular AA amyloid of chickens.379 None of these localized amyloidoses appears to be inherited, but expression may be influenced by genetic factors.