Steroid 5α-Reductase 2 Deficiency
A specific form of hereditary male pseudohermaphroditism termed pseudovaginal perineoscrotal hypospadias was defined on clinical and genetic grounds in 1961 by Nowakowski and Lenz67,68 and subsequently by Simpson et al.69 and by Opitz et al.70 This entity also has been called familial incomplete male pseudohermaphroditism type 2.71 Affected 46, XY males have an autosomal recessive disorder characterized by an external female phenotype at birth, bilateral testes, and normally virilized Wolffian structures that terminate in or empty into the vagina. While this eponym encompassed more than one disorder, the fact that the phenotype is usually the result of deficient production of dihydrotestosterone was established in 1974 by studies of two families with the disorder, one in Dallas71 and the other in the Dominican Republic.72,73 The entity is now termed steroid 5α-reductase 2 deficiency.
The initial studies in Dallas were performed in a 13-year-old 46,XY phenotypic girl with primary amenorrhea. She was partially virilized (Fig. 160-6A ), and plasma testosterone values were in the adult male range. Because of the virilization, the decision was made to remove the testes and to repair the external genitalia. The finding at surgery of normal male Wolffian duct structures—epididymides, vasa deferentia, seminal vesicles, and ejaculatory ducts that terminated in a blind-ending vagina—was characteristic of the phenotype of pseudovaginal perineoscrotal hypospadias (see Fig. 160-6B ). Dihydrotestosterone formation in tissue slices of foreskin, epididymis, and labia majora obtained at the time of surgery was virtually undetectable, establishing that deficiency in dihydrotestosterone formation was the cause.71 This interpretation was confirmed by studies of the 5α-reductase enzyme in fibroblasts cultured from the skin of affected individuals.51,74
External genitalia and internal ducts of a patient with 5α-reductase 2 deficiency; the patient is the propositus from Walsh et al.71 A. Photograph of external genitalia showing clitoromegaly and the opening of a blind-ending vagina. B. X-ray of the abdomen after the injection of diatrizoate sodium into the vasa deferentia at the time of abdominal exploration (vd = vas deferens; sv = seminal vesicles; ed = ejaculatory duct). The dye emptied into the vagina.
A similar conclusion as to the pathogenesis was reached by Imperato-McGinley and colleagues as the result of analyses of plasma and urinary steroids in a large family in the Dominican Republic with autosomal recessive male pseudohermaphroditism.72,73 Namely, the urinary excretion of 5α-androstanediol and androsterone (the end products of dihydrotestosterone metabolism) was low, as would be predicted if dihydrotestosterone formation were deficient.
The usual clinical features are summarized in Table 160-3 and include autosomal recessive inheritance; severe perineoscrotal hypospadias with a dorsal, hooded prepuce and a ventral urethral groove that opens at the base of the phallus; a blind-ending vaginal pouch of variable length; well-developed and histologically differentiated testes with normal epididymides, vasa deferentia, and seminal vesicles; absent Müllerian duct derivatives; and variable masculinization and no breast enlargement at the time of expected puberty.
Table 160-3: Features of Steroid 5α-Reductase 2 Deficiency |Favorite Table|Download (.pdf) Table 160-3: Features of Steroid 5α-Reductase 2 Deficiency
| External phenotype: Female genitalia with some clitoromegaly at birth and variable virilization at expected time of puberty; normal male breast development |
| Urogenital tract: Testes; epididymides, vasa deferentia, and seminal vesicles empty into vagina; no Müllerian duct derivatives |
| Karyotype: 46,XY |
| Inheritance: Autosomal recessive |
| Endocrinology |
|Testosterone: Normal male plasma levels and production rates |
|Dihydrotestosterone: Low or low normal male plasma levels and production rates |
|Estrogen: Normal male plasma levels and production rates |
|Gonadotropin: Normal to slightly elevated plasma LH levels |
| Pathogenesis: Inability to form dihydrotestosterone |
Most affected individuals are raised as females, despite the clitoromegaly that may be present at birth. It was recognized in the first two families evaluated by us that the phenotype can be variable; one affected sister in each family had a pseudovagina, whereas the other was more virilized and had only a single perineal orifice—a urethra that provided the outlet for a urogenital sinus.71,75,76 A sufficient number of families subsequently have been reported in the literature to make possible certain generalizations about the variability of manifestations71– 73,75– 99 (Table 160-4). Consanguinity is present in about a third, and the family history is positive in about 40 percent of families. Approximately 55 percent of patients have a blind-ending vagina (pseudovagina), as originally described by Lenz67,68 ; in 12 families, a urogenital sinus was present; and in 6 families, the phallus was sufficiently large at birth that the children were identified as males with hypospadias and raised as males. Occasional affected individuals have only a microphallus with a normal male urethra,100 but 5α-reductase deficiency is an unusual cause of microphallus.101
Table 160-4: Clinical Features in Steroid 5-Reductase 2 Deficiency |Favorite Table|Download (.pdf) Table 160-4: Clinical Features in Steroid 5-Reductase 2 Deficiency
|Feature ||Number Affected ||Percent |
|Documented consanguinity ||16/47 ||39 |
|Positive family history ||20/49 ||41 |
|Anatomic features || || |
|Pseudovagina ||18/33 ||55 |
|Urogenital Sinus ||12/33 ||36 |
|Hypospadias ||6/33 ||16 |
|Testes in inguinal canals, labia, or scrotum ||43/43 ||100 |
|Spermatogenesis, absent or profoundly impaired ||9/9 ||100 |
|Gynecomastia ||1/50 ||2 |
|How diagnosis established || || |
|Ratios of 5β/5α metabolites in urine ||13/46 ||28 |
|Ratios of testosterone: dihydrotestosterone in plasma (before or after hCG) ||46/47 ||98 |
|5α-Reductase measurements in biopsy tissue or fibroblasts ||31/47 ||66 |
|Gonadotropin values || || |
|Elevated luteinizing hormone ||10/23 ||43 |
|Elevated follicle-stimulating hormone ||12/23 ||52 |
|Gender role behaviour || || |
|Raised as male ||6/40 ||15 |
|Changed from female to male ||19/40 ||48 |
|Female ||9/40 ||22 |
|Too young to ascertain ||6/40 ||16 |
|Homozygotes ||23/37 ||61 |
|Compound heterozygotes or presumed compound heterozygotes ||13/37 ||32 |
The testes in all patients are extraabdominal—present in the inguinal canals, labia majora, or scrotum. Although sperm production is profoundly impaired or absent in most subjects in whom it has been examined, one affected man from the Dominican Republic family fathered a child after intrauterine insemination,102 and fertility has been reported in a family in which the disorder is associated with a male phenotype.103
In summary, the anatomic features range from minor to profound impairment of virilization of the external genitalia. The most consistent features are a small phallus and absence of the prostate. The nature of the variability in expression (even within families) is not clear, but one implication of this analysis is that this disorder must now be considered in the differential diagnosis of hypospadias (at least familial hypospadias).
Imperato-McGinley and colleagues reported that 18 of 19 individuals from the Dominican Republic who were raised as females changed gender role behavior to male at the time of expected puberty.77,104 A similar phenomenon has been described in 19 of the 40 families summarized in Table 160-4. Change in gender role behavior from female to male has been described in people with 17β-hydroxysteroid dehydrogenase 3 deficiency, in subjects with 45,X/46,XY gonadal dysgenesis, and in one individual with 3β-hydroxysteroid dehydrogenase II deficiency.105– 107 It is of interest that change in gender role behavior is not characteristic of mutations of the androgen receptor in which gender behavior usually conforms to the sex of rearing.
The gender role reversal in 5α-reductase deficiency has been described in different ethnic groups and in different social settings. This finding suggests that androgen action in utero, during the neonatal period, and/or at puberty has an impact on the determination of male gender identity that is so pervasive that it can override female sex assignment and female rearing.77,104 Whether these individuals actually undergo a true change of gender identity rather than a change in gender role behavior is not clear. Individuals with ambiguous genitalia may be aware of their abnormalities from an early age and consequently uncertain about their exact gender role prior to puberty.83 Furthermore, many individuals in whom gender role has changed from female to male at puberty have been raised in cultures in which the sexes have fairly rigid stereotypes as to sexual role and in which being male might be viewed as desirable.105 It seems safe to assume that psychosocial forces interact with hormonal factors in determining the sexual behavior of humans, but definitive studies into this problem are difficult because of limitations in the methods available for studying human behavior.
Two ancillary aspects of this phenomenon deserve comment. First, the New Guinean cluster of subjects with 5α-reductase deficiency108– 111 includes some people raised initially as females and some raised from the first as males. In this group, the disorder is sufficiently common that affected individuals are frequently recognized at birth and assigned initially to a third sex, but they eventually have the same type of difficulties fitting into adult life as do subjects with intersex in other parts of the world. Second, the first case of gender role reversal and indeed of steroid 5α-reductase 2 deficiency may have been Herculine Barbin, a nineteenth-century woman who changed her legal sex from female to male and whose phenotype, including evidence from autopsy, is compatible with the diagnosis.112
Simpson et al.69 showed that testosterone secretion in 5α-reductase deficiency is normal and is under normal feedback control. Subsequent studies have supported this interpretation. The characteristic endocrine features are as follows:
Normal male levels of plasma testosterone and low levels of plasma dihydrotestosterone71– 73
Elevation in the ratio of the concentration of plasma testosterone to dihydrotestosterone in adulthood and after stimulation with hCG in childhood73,89,93,113,114
Elevated ratios of urinary 5β- to 5α-metabolites of androgen73,87,88,93,113,114
Diminished conversion of testosterone to dihydrotestosterone in biopsied tissues71
Elevated ratios of urinary 5β- to 5α-metabolites of C-21 steroids87,95,114
Increased ratio of plasma testosterone to dihydrotestosterone after the administration of testosterone83,113
Levels of plasma LH are either normal71,83,88,97 or slightly elevated (although never as high as in men with primary testicular failure or in subjects with male pseudohermaphroditism due to abnormalities of the androgen receptor).72,73,79,95,96 In one study, elevation of plasma LH level was due to increased amplitude of LH pulses in the face of normal frequency of pulses.115 It is of interest in this regard that elevated LH was present in 10 of the 23 and elevated follicle-stimulating hormone (FSH) was described in 12 of the 23 subjects summarized in Table 160-4. This finding implies that dihydrotestosterone plays a role, probably minor, in the regulation of gonadotropin secretion.
Androgen and estrogen dynamics were studied in detail in the index case in the Dallas family71 (see Fig. 160-2B ); plasma levels of androstenedione (1.1 ng/ml) and testosterone (6.9 ng/ml) and the plasma production rates of androstenedione (2.7 mg/day) and testosterone (5.2 mg/day) were in the normal range for men. Estradiol production also was in the range for normal men (45 μg/day). The finding that androgen and estrogen production is in the normal male range explains the failure of patients to undergo female breast development at the time of puberty; in contrast, in subjects with mutations of the androgen receptor, variable feminization at the expected time of puberty correlates with increased estrogen secretion by the testes.
The enzymatic features of 5α-reductase deficiency were characterized in fibroblasts cultured from the genital skin, and two categories were recognized, namely, one group of patients with profound deficiency/absence of enzyme activity and another group in whom a normal amount of kinetically abnormal enzyme was synthesized.51,74– 76 The meaning of these functional studies became apparent only when the cDNAs for the 5α-reductases were cloned. Steroid 5α-reductase 1, the first of the cDNAs to be cloned, was established in formal genetic studies to be normal in patients with 5α-reductase deficiency.116 Subsequently, the cDNA for 5α-reductase 2 was cloned, and a number of mutations of the cDNAs for this protein have been documented in these families.12,117,118
Although plasma dihydrotestosterone levels are low,69– 71 they are always measurable and may fall within the low-normal range. The circulating dihydrotestosterone in this disorder could be synthesized by the residual activity of the mutant enzyme or derived from 5α-reductase 1. Studies of two groups of affected individuals clearly indicate that the latter source predominates. Indeed, New Guinean subjects who have a deletion of the entire coding sequence for 5α-reductase 2 enzyme12 and who, as a consequence, make no functional enzyme nevertheless have measurable plasma dihydrotestosterone.111 Likewise, one subject from a family with a splice junction abnormality that precludes synthesis of a functional steroid 5α-reductase 2 enzyme117 had basal plasma dihydrotestosterone levels in the low-normal range and supraphysiologic levels after he was given large amounts of testosterone propionate by injection for 3 days.83 These findings indicate that steroid 5α-reductase 1 contributes to plasma dihydrotestosterone, recognizing that in some patients dihydrotestosterone also may be formed in small amounts from the residual activity of mutated steroid 5α-reductase 2.117 The fact that 5α-reductase activity is normal in hair follicles from the scalps of patients with 5α-reductase deficiency119 suggests that androgen action in some tissues may be mediated by steroid 5α-reductase 1. Elucidation of the role of steroid 5α-reductase 1 in androgen physiology is a major imperative.
The degree of virilization at expected puberty can be striking, and in some subjects the habitus becomes masculine, although affected subjects virilize less completely than their unaffected brothers. This virilization could be mediated by the circulating dihydrotestosterone that is measurable in all subjects or could be due to the actions of testosterone itself over a long period; attempts to resolve this question have yielded inconclusive results.83 Namely, in four affected men, the parenteral administration of sufficient amounts of testosterone esters to elevate testosterone levels above normal for several months did promote virilization but simultaneously raised plasma dihydrotestosterone levels to normal. Consequently, it was not possible to deduce whether the virilization at puberty is mediated by testosterone or dihydrotestosterone. Testosterone can enhance transcription of some androgen-responsive reporter genes,35 but the fact that dihydrotestosterone is formed in men with 5α-reductase 2 deficiency and the fact that it binds more tightly to the androgen receptor32 suggest that dihydrotestosterone itself is the principal mediator of virilization at puberty, even in subjects with steroid 5α-reductase 2 deficiency.
Women in the Dominican Republic family who have homozygous mutations of the 5α-reductase 2 gene are endocrinologically normal,120 and two affected women who are endocrinologically normal (one homozygote and one compound heterozygote) were identified in another study.121 In those affected women in whom it was measured, plasma levels of 5α-reduced progesterone (5α-dihydroprogesterone) were normal during the luteal phase despite the 5α-reductase 2 deficiency.121 Since 5α-dihydroprogesterone is a major metabolite in the blood of women during the luteal phase122 and during pregnancy,123 the fact that the levels are normal in these women implies that this metabolite is formed by 5α-reductase 1. The physiologic role of 5α-reductase in women is still to be defined. It is of interest in this regard that steroid 5α-reductase 1 activity is necessary for normal gestation and delivery in the female mouse.124,125
Cloning of the 5α-reductase 2 cDNA made it possible to analyze the mutations in the disorder. Forty-five different mutations have been described to date, including 35 different missense mutations, 3 premature stop codons, 3 small deletions, 1 insertion of a nucleotide, and 1 change from a stop codon to a missense codon12,117,118,120,121,126– 141 (Fig. 160-7). In the New Guinea cluster, the entire coding sequence is deleted.12 Approximately two-thirds of patients have homozygous mutations (see Table 160-4), and one-fourth are compound heterozygotes. Mutations of only one allele have been found in some individuals, and no mutations were detected in one family with convincing endocrinologic evidence of 5α-reductase deficiency.119 We believe that the latter two groups are compound heterozygotes and homozygotes, respectively, for mutations that map outside the coding exons and the immediate flanking intron sequences.
Mutations in the steroid 5α-reductase 2 gene and protein. A schematic diagram of the 5α-reductase 2 gene is shown in the middle. On the left are the locations of 45 different mutations, and the sites of several recurring mutations are shown on the right. (NG represents the deletion of the gene in the New Guinea cohort. The initiating methionine is designated Met in exon 1, and the normal termination codon is designated with an asterisk in exon 5.) The various mutations have been reported as follows: G34R,G→A,117,126,127 G34R,G→C,117,126 L55Q117,126,128,129 Q56R,117,126 P59R,126 Y91D,126 R103*,126, 359ΔTC,117 l112N,128,130 G115D,117,126,127,131 Q126R,117,126,128,130,132,133 R145W,126 M157Δ,128,130 134,136 D164V,117,126,132 R168C,132 R171S,117,126 P181L,126 G183S,117,120,126,131,132 N193S,117,126,133 G196S,117,126,128,130,135 E197D,117,126 E200K,137 G203S,127 A207D,117,126,127 L224P,117,126 R227Q,128,130,135 R227*,117,132,138 A228T,128,130,135 H230P,126 H231R,117,126,128,130,133,139 725 + 1,G→T,117,120 Y235F,126, R246W,117,120,121,126,131,132,140 R246Q,117,121,126 *255Q,132,141 ΔNG.12 Several of these mutations are being reported for the first time: A49T, W53*, W53G, I112R, ΔG443, 458insA, Y235H, A248D (D Davis, DW Russell, unpublished observations.)
The mutations are distributed throughout the coding sequence. No affected individual had more than two of the mutations shown in Fig. 160-7, and none of these mutations has been detected in the normal individuals screened to date. Most missense mutations cause abnormalities of NADPH binding or impair binding of testosterone to the enzyme. Other mutations cause a premature termination codon, gene deletions (both complete and partial), or splice-junction abnormalities. The cDNAs for several of the missense mutations have been expressed in cultured cells, and the residual enzyme activities have been characterized in detail.126
Identical mutations have been discovered in different ethnic groups (see Fig. 160-7). In some instances, this recurrence is probably due to a founder effect. For example, the same missense mutation (R171S) has been described in both Sicily and Malta, and it is likely that a heterozygous carrier from one of these islands was responsible for the spread of the R171S mutation. In other instances, for example, the appearance of the R246W mutation in Egypt, Brazil, and the Dominican Republic may be due to recurring mutations. Formal genetic testing to establish which mutations are recurrent and which are ancient has not been performed.
Three large clusters of patients with 5α-reductase deficiency have been described in different parts of the world—the Dominican Republic family involving some 38 members,68,69 the Turkish cluster of 12 subjects,95,141 and 13 affected members of the Sambia tribe in the New Guinea highlands.108– 111 The high incidence of the disorder in these groups is probably due to a founder effect in geographic isolates of people with a high coefficient of inbreeding. It is of interest in this regard that the Turkish kindred also has a high incidence of another rare autosomal recessive trait, 17β-hydroxysteroid dehydrogenase 3 deficiency.141
The diagnosis of 5α-reductase deficiency is usually made either at the time of expected puberty or in infancy. In the adolescent or young adult, diagnosis is usually straightforward—a 46,XY male pseudohermaphrodite with the characteristic phenotype, male plasma testosterone levels, and abnormal ratios of plasma testosterone to dihydrotestosterone or abnormal ratios of urinary 5β- to 5α-steroid metabolites (see Table 160-4). Because the phenotypes can overlap, it is necessary to distinguish 5α-reductase deficiency from defects in testosterone biosynthesis on the one hand and partial defects of the androgen receptor on the other. In all three types of disorders, virilization of the Wolffian ducts can be more complete than that of the external genitalia. Defects in testosterone biosynthesis usually cause low plasma testosterone levels, but in men with partial enzyme defects, testosterone can be normal at the expense of high LH values and increased levels of precursor steroids. The most common hereditary defect in testosterone biosynthesis, 17β-hydroxysteroid dehydrogenase 3 deficiency, can be recognized on the basis of elevated androstenedione levels,142 and it is our practice to measure androstenedione routinely in suspected cases of 5α-reductase deficiency. Separation of the disorder from the Reifenstein syndrome also can be perplexing, since defects of the androgen receptor can impair the development of tissues that are major sites of dihydrotestosterone biosynthesis and hence cause secondary 5α-reductase deficiency and high ratios of plasma testosterone to dihydrotestosterone.143,144 In this situation, detailed family histories indicating the pattern of inheritance, careful phenotypic characterization to determine whether gynecomastia is present, and measurements of the ratios of urinary 5β- to 5α-glucocorticoid metabolites (which mainly reflect hepatic metabolism) usually establish the true diagnosis.
Recognition of 5α-reductase deficiency in infants and prepubertal children presents special problems, particularly when the family history is uninformative. In this situation, determination of the ratios of plasma testosterone to dihydrotestosterone before and after administration of hCG generally serves to establish the diagnosis.132,135,145 When the testes have been removed, the diagnosis can be established either by determining the ratio of urinary 5β- to 5α-glucocorticoid metabolites114,145 or by determining the ratio of plasma testosterone to dihydrotestosterone after the administration of testosterone esters by injection.85
For individuals raised as males or who elect to function as males, several procedures are appropriate. First, urologic consultation should be obtained regarding appropriate corrective surgery to repair chordee, correct hypospadias, and bring cryptorchid testes as low as possible into the labioscrotal folds. Second, since the degree of virilization is generally unsatisfactory, supplemental androgen therapy may be indicated. The ideal agent would be one that replaces the missing dihydrotestosterone; in experimental studies, the administration of dihydrotestosterone enanthate by injection at 4- to 6-week intervals results in a sustained elevation of plasma dihydrotestosterone levels,146 but at present the agent is not available for general use. A second approach is to administer testosterone esters in quantities sufficient to elevate the plasma testosterone to supraphysiologic levels; in patients with 5α-reductase deficiency, such regimens bring dihydrotestosterone levels to the normal male range and promote virilization83 (Fig. 160-8); it is not known whether such high doses of testosterone are safe over the long term. A third approach is to administer an androgen that does not require 5α-reduction to be active. For example, 19-nortestosterone can be given by injection in an esterified form such as nandrolone decanoate.147 A fourth approach is the administration of a dihydrotestosterone cream by inunction; this regimen raises plasma dihydrotestosterone levels and can cause considerable phallic growth in infants.80 Although administration of dihydrotestosterone cream appears to be safe over the short term, the long-term efficacy and safety have not been established.148 While these regimens do promote virilization, most men in whom androgen therapy is instituted in adulthood do not have growth of the phallus into the normal range; whether earlier diagnosis and treatment will result in more successful virilization is not clear at present.132
Patient with 5α-reductase 2 deficiency before and after high-dose androgen therapy. Left. Before treatment (June 1976). Right. After treatment with a mixture of testosterone esters 500 mg intramuscularly weekly (March 1980). Correction of chordee was performed between these dates. (From Price et al.83 Used by permission.)
In subjects who elect to live as women, the management is similar to that in women with testicular feminization and allied syndromes (see below) but should be undertaken only after rigorous psychiatric and psychological evaluation to establish beyond reasonable doubt the presence of a female gender identity. In such women, the testes should be removed to preclude (or stop) virilization, estrogen-progestogen therapy should be instituted at an appropriate age to feminize, and when appropriate, vaginoplasty should be undertaken either by surgical or medical means.61
Disorders of the Androgen Receptor
Disorders of the androgen receptor can cause several distinct phenotypes. Despite differences in the clinical manifestations, these disorders are similar with regard to endocrinology, genetics, and basic pathophysiology.
Clinical Features of Complete Testicular Feminization (Complete Androgen Insensitivity Syndrome).
The clinical features of complete testicular feminization are summarized in Table 160-5. The syndrome has been recognized for many years (the early literature has been reviewed by Hauser149). The initial insight into the pathogenesis was provided by two pioneering studies. First, in 1937, Pettersson and Bonnier deduced from family studies that affected individuals are genetic males, that the pattern of inheritance is consistent with X-linked transmission, and that the syndrome could best be explained by a failure of male development in an embryo in which the fundamental trend is toward the female phenotype.150 Second, soon after Morris introduced the term testicular feminization to describe the disorder,2 Wilkins deduced that the pathogenesis is due to resistance to the action of androgen.3
Table 160-5: Clinical Features of Complete Testicular Feminization |Favorite Table|Download (.pdf) Table 160-5: Clinical Features of Complete Testicular Feminization
| External phenotype: Female external genitalia with underdevelopment of the labia and a blind-ending vagina, female habitus and breast development, paucity of axillary and pubic hair |
| Urogenital tract: Testes that may be intraabdominal, along the course of the inguinal canal, or in the labia; absent Wolffian and Müllerian derivatives |
| Karyotype: 46,XY |
| Inhertance: X-linked recessive |
| Endocrinology: |
|Testosterone: Normal or high male plasma levels and production rates |
|Estrogen: Plasma levels and production rates higher than in normal men |
|Gonadotropin: Elevated plasma LH levels |
| Pathogenesis: Complete resistance to all actions of testosterone and dihydrotestosterone |
The clinical manifestations have been reviewed.149,151 The typical subject is seen by a physician either because of primary amenorrhea (postpubertally) or an inguinal hernia (prepubertally). In a 2-year survey in the United Kingdom, 76 percent of cases in infants were ascertained on the basis of unilateral or bilateral inguinal hernias, and one or two gonads could be palpated in most of these babies.152 On occasion, the diagnosis is not established until late in life.153 Breast development is that of a normal woman, and the general body habitus and distribution of body fat are female in character (Fig. 160-9 A). Axillary and pubic hair is absent or scanty, but some vulvar hair (albeit diminished in amount) is usually present. Facial and scalp hair is that of normal women. The external genitalia are unambiguously female (Fig. 160-10 A). The labia and clitoris are normal or somewhat underdeveloped. Although usually adequate for successful coitus, the vagina may be absent or shallow. The vagina, if present, is blind-ending, and the internal genitalia are absent except for gonads that have the histologic features of undescended testes (i.e., normal or increased Leydig cells and seminiferous tubules without spermatogenesis). The testes may be located in the abdomen, along the course of the inguinal canal, or in the labia majora. Remnants of Müllerian or Wolffian duct origin can be identified in the paratesticular fascia or in fibrous bands extending from the testes,149,154,155 and rarely, uterine remnants are present.156– 159 It is of interest in this regard that levels of anti-Müllerian hormone are elevated in affected children.160
A. Complete testicular feminization. B. Incomplete testicular feminization. C. Reifenstein syndrome. (From Griffin and Wilson.61 Used by permission.)
External genitalia of four subjects with disorders of androgen receptor function. A. Complete testicular feminization. B. Incomplete testicular feminization. C. Reifenstein syndrome (prepubertal). D. Reifenstein syndrome (adult). (From Griffin and Wilson.61 Used by permission.)
Documentation that nuclear chromatin is male in character161,162 and that the chromosomal complement is 46,XY163– 165 confirmed the deductions from pedigree analysis and gonadal histology that affected individuals are genetic males. Affected subjects tend to be rather tall for women, averaging 171.5 cm in height in one series166 ; bone age corresponds to chronologic age149 ; body size is larger than average166 ; tooth size is as large as in normal men (and larger than in normal women)167 ; and the cranial dimensions and dental arch dimensions and occlusion are larger than in normal women.168,169 The fact that these parameters are larger than in normal women indicates that the Y chromosome may have direct effects on the teeth and skeleton that are not mediated by androgens. A possible role of estrogens has been postulated to explain the acceleration of linear growth.170 Adrenal and thyroid function are normal, and there are no commonly associated somatic anomalies.149 Intelligence is normal,171 and psychological development is feminine in regard to behavior, outlook, and maternal instincts.172
Estimates of incidence vary from 1 in 20,000 to 1 in 64,000 male births.149,173 On the basis of studies of buccal smears, as many as 1 to 2 percent of girls with inguinal hernias may have the disorder.173,174 In a survey in Japan, testicular feminization was the most common form of primary resistance to hormone action, with some 390 patients having been ascertained in a 10-year period.175 In one series this disorder was the third most frequent cause of primary amenorrhea in women after gonadal dysgenesis and congenital absence of the vagina.176
Except for psychological problems related to the infertility and the complications of cryptorchid testes, these women are usually healthy and have normal life spans. However, in one study a decrease in trabecular bone density was observed in eight women with testicular feminization,177 and in another study five adult women had decreased density of the lumbar spine.178 Most of the women in these studies had been castrated so that the extent to which these changes are due to estrogen deprivation and/or inadequate estrogen replacement is not clear, but one 17-year-old subject with intact testes had decreased bone density.179
These women have a profound resistance to the action of both exogenous and endogenous androgens. Wilkins3 gave methyltestosterone in large doses to women with testicular feminization after castration and showed that there was no growth of pubic or axillary hair (despite documentation of pubic hair follicles by biopsy), no enlargement of the clitoris, no change in the voice, and no other detectable virilizing effect. Subsequent work confirmed the lack of response of pubic hair to androgen treatment180,181 and also demonstrated resistance to androgen in regard to sebum production,181 failure of the expected decrease in thyroxine-binding globulin levels in plasma,182,183 diminished feedback on LH secretion by the pituitary,184 and lack of effect on phosphorus and nitrogen balance.185– 187 Thus resistance to the action of androgen appears to be virtually absolute in complete testicular feminization.
The histologic features of the testes are similar to those of testes in other forms of cryptorchidism but differ in that spermatogenesis is consistently absent (whereas spermatogenesis is present in half of age-matched cryptorchid testes due to other causes), germinal elements are detected rarely, and Sertoli cell adenomas are frequent.188– 190 Although the number of Leydig cells per high-power field is increased,189 the total volume and number of Leydig cells are probably normal.191 Malignant tumors are usually germ cell tumors, particularly seminomas,192 but malignant sex cord stromal tumors also occur.193 It is probable that the incidence of tumors is no greater than in other cryptorchid testes.189
Clinical Features of Incomplete Testicular Feminization.
The term incomplete testicular feminization was introduced to characterize a phenotype similar to that of complete testicular feminization but associated with partial virilization of the external genitalia and mixed virilization and feminization at expected puberty.194 The term was used subsequently to characterize several types of incomplete male pseudohermaphroditism, including defects of testosterone synthesis, the Reifenstein syndrome, and some subjects for whom data are insufficient to determine the diagnosis. Nevertheless, certain of these subjects with abnormalities of the androgen receptor constitute a distinct phenotype195– 198 (Table 160-6).
Table 160-6: Clinical Features of Incomplete Testicular Feminization |Favorite Table|Download (.pdf) Table 160-6: Clinical Features of Incomplete Testicular Feminization
| External phenotype: Clitoromegaly and/or partial fusion of the labioscrotal folds, female habitus and breast development, normal axillary and pubic hair |
| Urogenital tract: Testes that may or may not be cryptorchid, Wolffian duct derivatives emptying into the vagina, no Müllerian duct derivatives |
| Karyotype: 46,XY |
| Inheritance: X-linked recessive |
| Endocrinology: |
|Testosterone: Normal or high male plasma levels and production rates |
|Estrogen: Plasma levels and production rates higher than in normal men |
|Gonadotropin: Elevated plasma LH level |
| Pathogenesis: Partial resistance to the action of testosterone and dihydrotestosterone |
Affected individuals have the habitus and general appearance of women and, as in the complete form of the disorder, usually present because of primary amenorrhea (see Fig. 160-9 B). The karyotype is 46,XY; the testes are in the abdomen or in the inguinal canals and are histologically indistinguishable from those in complete testicular feminization. The external genitalia are distinctive in that the labioscrotal folds are partially fused, and clitoromegaly may be present (see Fig. 160-10 B). The vagina is short and ends blindly.
At the expected time of puberty, variable degrees of feminization and virilization may occur. Müllerian duct derivatives are usually absent, but Wolffian duct structures are present; this latter feature, together with the partial virilization of the external genitalia, separates the phenotype from that of testicular feminization. Not only are upper Wolffian duct structures present (epididymides and vasa deferentia), but in addition, terminal Wolffian duct derivatives, including the ampullae of the vasa deferentia, the seminal vesicles, and the ejaculatory ducts, are male in character (although underdeveloped in comparison with normal men). The ejaculatory ducts empty into the vagina. Thus certain features resemble testicular feminization (female breast development), some resemble 5α-reductase deficiency (presence of male Wolffian duct derivatives and ambiguous external genitalia), and some resemble the Reifenstein syndrome (mixed virilization and feminization at expected puberty). The frequency of this disorder is uncertain, but in most series (including our experience) it is about one-tenth as common as complete testicular feminization.
Clinical Features of the Reifenstein Syndrome (Partial Androgen Insensitivity Syndrome).
In some families, male pseudohermaphroditism that is typically less severe than in incomplete testicular feminization is inherited as an X-linked recessive trait. Although the usual phenotype is male, affected men within a given family may have a spectrum of abnormalities ranging from almost complete failure of virilization to nearly complete masculinization. The disorder has been described under a variety of terms, including Reifenstein syndrome,199– 200 Lubs syndrome,201 Gilbert-Dreyfus syndrome,202 Rosewater syndrome,203 and familial incomplete male pseudohermaphroditism type 1,204 but the common appellation is Reifenstein syndrome. The fact that these disorders are variable manifestations of similar mutations was deduced from pedigree analyses. The most extensive family reported is the one studied by Ford205 and by Walker et al.206 In this family, the manifestations in 12 affected men ranged from moderate abnormalities (microphallus and gynecomastia) to intermediate defects of virilization (hypospadias) to such severe defects of virilization (complete failure of scrotal fusion) that three affected family members were identified initially as females.206 In another family reported originally by Bowen et al.200 and subsequently by Wilson et al.,204 the phenotype also ranged from a moderate defect in virilization in two (microphallus and bifid scrotum) to a more severe abnormality in eight (perineoscrotal hypospadias) to almost complete male pseudohermaphroditism in one (perineoscrotal hypospadias, no vas deferens, and a vaginal orifice). The phenotypic variability in this family is illustrated in Fig. 160-11. In a third family, described by Gardo and Papp,207 three of four affected individuals were phenotypic females, whereas the fourth had perineoscrotal hypospadias, bifid scrotum, and gynecomastia typical of the Reifenstein syndrome. Variability in phenotypic expression also has been noted in other families with the disorder.208,209
Pedigree of a family with Reifenstein syndrome. (From Grino et al.263 Used by permission.)
The features are summarized in Table 160-7. The most common presentation is a 46,XY male with perineoscrotal hypospadias, azoospermia with infertility, incomplete virilization, and gynecomastia that develops at expected puberty (see Fig. 160-9 C). The external genitalia of an affected child and an affected adult are shown in Fig. 160-10 C and D, respectively. Axillary and pubic hair is normal, but chest and facial hair is absent or sparse. Temporal recession of the hairline is minimal, and the voice tends to be somewhat high-pitched. Less severely affected men may exhibit only a bifid scrotum, infertility, and incomplete virilization at puberty. More severely affected individuals can have incomplete Wolffian duct structures and formation of a vagina; only by identification of less severely affected members within the same family can severely affected subjects be distinguished from those with incomplete testicular feminization. Partial virilization of the urogenital sinus results in a prostatic utricle but no true prostate. The lower ejaculatory duct system has not been characterized in detail.
Table 160-7: Clinical Features of the Reifenstein Syndrome |Favorite Table|Download (.pdf) Table 160-7: Clinical Features of the Reifenstein Syndrome
| External phenotype: Usually a male with perineoscrotal hypospadias, normal axillary and pubic hair, but scant beard and body hair; breast enlargement at time of expected puberty |
| Urogenital tract: Testes often cryptorchid, Wolffian duct structures vary in the degree of the male development, no Müllerian duct derivatives |
| Karyotype: 46,XY |
| Inheritance: X-linked recessive |
| Endocrinology: |
|Testosterone: Normal or high male plasma levels and production rates |
|Estrogen: Plasma levels and production rates higher than those in normal men |
|Gonadotropin: Elevated plasma LH levels |
| Pathogenesis: Variable resistance to the action of testosterone and dihydrotestosterone |
Cryptorchidism is common, and the testes on average are small (although usually larger than in Klinefelter syndrome). Leydig cells are usually normal by histologic examination, but Leydig cell neoplasia has been described.210 Spermatogenic tubules contain both Sertoli cells and germinal epithelium, but the germ cells do not mature beyond the primary spermatocyte stage. Hyaline degeneration of the tubules is often present.200
Most affected individuals are raised as men. Although the number of reported subjects is small and no in-depth psychological studies have been performed, gender identity/behavior in affected subjects raised as men seems to be unambiguously male, and some have had successful marriages. Presumably because of incomplete development of the prostate and ejaculatory system, however, ejaculate volume is characteristically small. Infertility is a consistent feature and appears to be the result of defective spermatogenesis and possibly of the anatomic abnormalities of the ejaculatory system.
Clinical Features of Men with Infertility or Undervirilization due to Androgen Resistance.
In a study of a family with the Reifenstein syndrome, some affected men were identified who were infertile but otherwise phenotypically normal. They had the same apparent degree of androgen resistance, as assessed by endocrinologic criteria,204 and the same abnormality of the androgen receptor in cultured skin fibroblasts as the more severely affected relatives.211 Gynecomastia was variable and late in appearance. Thus the Reifenstein syndrome can encompass both mild and severe phenotypic evidence of androgen receptor deficiency. Subsequently, it was recognized that some men with infertility or undervirilization but without a family history of the Reifenstein syndrome have endocrine evidence of androgen resistance and androgen receptor abnormalities similar to those in individuals with familial Reifenstein syndrome.212– 221 The clinical features are summarized in Table 160-8. Such men have normal male external genitalia, apparently normal Wolffian duct structures, and variable sperm production. Some have a small phallus, minimal beard and body hair, and gynecomastia. The prevalence of this form of androgen resistance as a cause of male infertility in normally virilized men is not established, but in some series it accounts for a significant fraction of male infertility associated with idiopathic azoospermia or severe oligospermia.222,223 Some affected men are fertile.218
Table 160-8: Clinical Features of Men with Infertility or Undervirilization Due to Androgen Resistance |Favorite Table|Download (.pdf) Table 160-8: Clinical Features of Men with Infertility or Undervirilization Due to Androgen Resistance
| External phenotype: Normal man, variable small phallus, beard and body hair, and gynecomastia |
| Urogenital tract: Testes, fertility with variable sperm density or infertility associated with azoospermia or extreme oligospermia, Wolffian duct structures of normal men, no Müllerian duct derivatives |
| Karyotype: 46,XY |
| Inheritance: X-linked recessive |
| Endrocrinology: |
|Testosterone: Plasma levels and production rates of normal men or slightly higher |
|Estrogen: Production rates usually higher than in normal men |
|Gonadotropin: Plasma LH levels normal or elevated |
| Pathogenesis: Resistance to the action of androgen varies in different tissues |
The endocrine features are similar in all forms of androgen receptor disorders but have been characterized best in subjects with complete testicular feminization. The early deductions by Morris2 and Wilkins3 that androgen production is normal in patients with testicular feminization have been confirmed and extended. Plasma levels of testosterone are either in the normal male range or somewhat higher than those of normal men,7,224– 228 a phenomenon that is probably due to two factors: (1) the subjects have elevated estrogen production rates (see below) that result in an increase in the level of testosterone-binding globulin in plasma, and (2) production rates of testosterone tend to be somewhat higher than in normal men.7 As in normal men, testosterone is produced in the testes.24,225,229 In one study, testosterone production in women with testicular feminization averaged about 50 percent higher than in normal men (8.3 versus 5.7 mg/day) but was only higher in women with inguinal testes and not in those with intraabdominal testes7 (see Fig. 160-2C ).
The elevated testosterone production rate is presumably secondary to high levels of LH in plasma, which in turn are the consequence of defective feedback regulation because of resistance at the hypothalamic-pituitary level to the feedback effects of androgen on LH production.184,227,228,230 In addition, elevated estradiol levels in the disorder may cause positive feedback on LH production.231 The elevated plasma LH levels are due both to more frequent and greater amplitude of LH secretory pulses than in normal men.228 Further increase in plasma LH levels after the administration of luteinizing hormone-releasing hormone (LHRH) is within the normal range.228 Plasma levels of FSH are usually normal.228 Although the negative-feedback regulation of LH secretion by androgens is defective in testicular feminization, LH secretion in these patients is influenced by estradiol—the administration of the antiestrogen clomiphene citrate causes a further increase in plasma LH, and plasma LH also rises further after castration.
The origin of estrogen in four women with testicular feminization is illustrated in Fig. 160-2C 7 ; the mean production rates of estrone and estradiol, respectively, were 114 and 77 μg/day (versus 66 and 45 μg/day, respectively, in normal men). Testicular estradiol secretion in these women averaged 42 μg/day (versus 6 μg/day in normal men). Thus most of the increased estradiol production is due to secretion by the testes. This finding is in keeping with the reports by Kelch et al.24 and by Laatikainen et al.229 that levels of estradiol in spermatic vein blood are high in women with testicular feminization.
To summarize, resistance to the feedback regulation of LH production by circulating androgen results in elevated plasma LH levels, and this in turn results in the enhanced secretion of both testosterone and estradiol by the testes. The fact that hCG levels rise even higher (and that symptoms of menopausal flushing develop) when the testes are removed is consistent with the view that gonadotropin secretion is under some type of regulatory control; presumably, in the steady state and in the absence of an effect of androgen, estrogen regulates LH secretion in subjects with testicular feminization. This feedback control is accomplished at the expense of a higher plasma estrogen level than in normal men.184,232
Endocrine findings in individuals with less severe forms of androgen resistance are similar to those in women with complete testicular feminization. In women with incomplete testicular feminization, plasma levels of testosterone are similar to those of normal men,233,234 and in one such subject the daily production rate of testosterone was greater (12.0 mg/day)198 than the average in normal men.7 Plasma LH levels198,233,234 and estrogen production rates and estrogen secretion by the testes198 are also elevated. Interestingly, administration of a large amount of estradiol benzoate to a subject with incomplete testicular feminization (to simulate the preovulatory surge of estradiol in normally cycling women) resulted in an LH surge similar to that of normal women.235 Urinary gonadotropin excretion is elevated in men with the Reifenstein syndrome,206 and plasma LH and testosterone levels are high on average,204 indicating defective feedback control of LH secretion at the hypothalamic-pituitary level. When LHRH is administered to subjects with Reifenstein syndrome, the surge in plasma LH is either normal or high.228,236,237 Furthermore, plasma LH does not decrease after the administration of medroxyprogesterone acetate,204 testosterone,238 or dihydrotestosterone.228 As in complete testicular feminization, steady-state control of LH secretion is regulated by estradiol.237 The production rates for plasma testosterone (9.2 mg/day) and for estradiol (199 μg/day) are high; three-fourths of the estradiol (147 (g/day, 10 times the normal amount) is secreted directly into the circulation, presumably from the testes204 (see Fig. 160-2D ).
The endocrine changes in infertile or undervirilized men with androgen resistance are similar to but less marked than those in men with other types of androgen receptor defects. Specifically, plasma production rates of testosterone and plasma levels of LH are normal to high, and estradiol production rates are normal or slightly elevated.212,218,220
The mechanism by which feminization occurs in individuals with receptor defects is clear. In each disorder, androgen resistance can cause a high mean level of plasma LH, elevated estradiol secretion by the testes, and feminizing signs at puberty. However, there is no direct relation between the absolute amount of estrogen secretion and the degree of feminization. Indeed, two phenotypic men with Reifenstein syndrome had higher estrogen secretion rates166 than any found to date in either complete or incomplete testicular feminization. We conclude that feminization in subjects with androgen resistance requires increased estradiol production but that the degree of feminization is influenced by the severity of the androgen resistance. It follows that the failure to feminize in some infertile men with androgen resistance is due both to less severe resistance to the action of androgen and to an inconsistent increase in estradiol formation.
Dihydrotestosterone formation is low on average in skin slices from patients with complete testicular feminization,71,195,239 and in some testicular feminization patients the excretion of dihydrotestosterone metabolites in urine is also decreased.240,241 This decrease in dihydrotestosterone formation is believed to be secondary to a decrease in the mass of the androgen target tissues that normally form dihydrotestosterone.143 Dihydrotestosterone formation is normal in fibroblasts cultured from most biopsies of genital skin from such individuals.51 Furthermore, in genital skin biopsies from subjects with incomplete testicular feminization198 and the Reifenstein syndrome204 and in fibroblasts cultured from the skin of such individuals, dihydrotestosterone formation is normal.51,242 Thus, on endocrine, genetic, and phenotypic grounds, these individuals are distinct from subjects with 5α-reductase 2 deficiency.
The basic study that allowed the pathogenesis of these disorders to be unraveled was the observation by Keenan and coworkers that the androgen receptor is present in fibroblasts cultured from the skin of normal subjects.243,244 Receptor content is greater in fibroblasts cultured from genital skin (foreskin, scrotum, labia majora) than from nongenital sites.211 The receptor in normal fibroblasts has a dissociation constant of approximately 0.2 nM for dihydrotestosterone and is the same intracellular androgen receptor as in androgen target tissues. Keenan et al. showed that fibroblasts grown from some women with complete testicular feminization showed no detectable dihydrotestosterone binding,244 a finding that was confirmed in other laboratories.211,245 The finding of absent receptor binding in fibroblasts from some women with testicular feminization provided an explanation for the profound androgen resistance in this disorder.
Other subjects with complete testicular feminization have receptor binding that is demonstrable but qualitatively abnormal. Identification of such a phenomenon came first from studies of thermolability of binding in two sisters with complete testicular feminization,246 and similar thermolability was reported in other patients.216,247,248 Qualitative abnormalities of the receptor were identified subsequently by a variety of tests of receptor function in individuals with androgen resistance, including failure of molybdate to stabilize the 8S androgen receptor complex,216,249,250 decreased affinity of ligand binding to the receptor,144,214,247,251– 253 impairment of nuclear retention of the binding ligand,254 failure of androgens to up-regulate the level of androgen receptor,216,251,252,255– 258 increased rate of dissociation of ligand from receptor,216,220,247– 252,259– 262 and lability of the androgen receptor under transforming conditions.34
The characteristics of the androgen receptor binding in fibroblasts grown from biopsies of individuals from 130 families studied in our laboratory who fulfill the phenotypic and endocrine requirements to be designated androgen resistant are summarized in Fig. 160-12.4 Receptor binding is designated qualitatively abnormal when it is measurable in intact cells and exhibits thermolability, instability in cytosol on sucrose gradients, or increased dissociation. In 33 families, binding was absent or nearly absent, most commonly in association with complete testicular feminization. Qualitatively abnormal receptor binding was the most common binding abnormality identified (56 families) and was present in each of the four clinical syndromes. A decreased amount of apparently normal receptor was present in subjects in 18 families, usually in individuals with a predominant male phenotype.263 In 23 families with endocrine and phenotypic evidence of androgen resistance, androgen receptor binding was normal both in quality and quantity. Androgen resistance with normal androgen binding was originally called receptor-positive resistance or postreceptor resistance.264– 273 Some families reported in this category264 were shown subsequently to have qualitatively abnormal receptor binding.247 The most important deduction drawn from the functional studies of the receptors was the recognition that the mutated androgen receptors have different characteristics in almost every family.
Androgen binding in cultured genital skin fibroblasts from 130 families with androgen resistance of the receptor type. The type of androgen binding in clinical syndromes of androgen resistance is shown. Each dot represents a family in which one or more persons were found to have a particular type of androgen binding, as measured by saturation analysis of dihydrotestosterone binding in cultured genital skin fibroblasts. Androgen binding was considered undetectable if it measured less than 4 fmol/mg protein. Binding was considered qualitatively abnormal if the androgen receptor in cultured fibroblasts was thermolabile or unstable or if the dihydrotestosterone-androgen receptor complex in intact cells dissociated at an increased rate. Binding was considered to be decreased if the amount was less than normal but no qualitative abnormality could be detected. (Adapted with permission from Griffin.4 )
In 1937, Pettersson and Bonnier concluded on the basis of pedigree analysis that testicular feminization could be due either to an X-linked recessive trait or to an autosomal trait that is manifested only in genetic males,150 and it was deduced subsequently that the disorder is X-linked. Similar mutations have been described in dogs,274 cows,275 rats,276 mice,277,278 horses,279 chimpanzees,280 raccoon dogs,281 and cats.282 In mice, X-linkage of the mutant gene was established by mapping techniques.277 Because all known instances in which genes are X-linked in one species are also X-linked in other species,283 documentation of X-linkage for the gene in mice suggested that the mutation is on the X chromosome in other species as well. Meyer et al.284 reported that skin fibroblasts cloned from an obligate heterozygote for complete testicular feminization consisted of two populations, some with deficient androgen binding and others with normal binding. This finding was consistent with random inactivation of one X-linked allele in each cell, as would be predicted by the Lyon hypothesis,285 and indicated X-linkage for the gene that encodes the androgen receptor. X-linkage for this gene was confirmed by Migeon and coworkers with the use of mouse-human hybrid cells286 and by similar studies in a family with a qualitatively abnormal androgen receptor.287 Evidence for X-linkage of the syndrome of incomplete testicular feminization246 and the Reifenstein syndrome199,200,204– 209 provided support for the concept that these disorders have a common pathogenesis. More important, using an informative restriction-fragment polymorphism, the mutant gene in one large family with Reifenstein syndrome was shown to be either tightly linked to or to involve the same gene responsible for testicular feminization.288 Demonstration of qualitatively abnormal receptor binding in some Reifenstein families254,289 and in some infertile and/or undervirilized men216,220,222 also indicated that these disorders involve the same gene product as testicular feminization.
The cloning of the cDNA for the human androgen receptor and confirmation of the X-linkage of the gene13– 16 made it possible to develop techniques to characterize mutations,290– 292 including Southern blot analyses to detect large deletions, exon amplification by the polymerase chain reaction followed by sequencing to detect point mutations, measurements of androgen receptor mRNA,291,293 immunoblots of receptor protein,294 assessment of functional capacity using reporter genes fused to androgen response elements,295,296 estimation of receptor function in intact cells infected with an adenovirus containing an androgen-responsive reporter gene,297 and single-strand DNA conformational polymorphism analysis.298
The mutations in this gene have been the subject of reviews,299,300 and as of February 1999, more than 321 different mutations of the androgen receptor had been reported to be associated with androgen resistance and recorded in the McGill University database, as reported by Gottlieb et al.301 (available on the Internet at http://www.mcgill.ca/androgendb/ ) (Fig. 160-13 and Table 160-9). Mutations that have been described only in prostate cancer (and hence may not cause androgen resistance)301 and the various expansions of the polyglutamine tract associated with the Kennedy syndrome (see Chap. 161) are not shown. It is noteworthy that most cDNAs sequenced to date are from patients with complete testicular feminization rather than from patients with less severe forms of androgen resistance, and consequently, the tentative mutation map shown in Fig. 160-13 may not be representative of all disease categories. Nevertheless, the mutations described to date are diverse and include partial or complete gene deletions, mutations that result in aberrant splicing of androgen receptor mRNA, mutations in the untranslated region of the gene, and nucleotide replacements that cause either the introduction of premature termination codons or amino acid substitutions.
Schematic representation of the mutations of the human androgen receptor that cause androgen resistance states as registered in the McGill University database. (As of 1998. An update is available in Gottlieb et al.301 and on the Internet at http://www.mcgill.ca/androgendb. ) The eight coding exons are numbered and are separated by seven introns. Missense mutations are indicated above the exons, and premature termination codons, small deletions, and splicing defects are shown below the exons. Large deletions and mutations that have only been reported in prostate cancer are not shown.
Table 160-9: Mutations of the Androgen Receptor that Cause Androgen Resistance as Recorded in the Database. |Favorite Table|Download (.pdf) Table 160-9: Mutations of the Androgen Receptor that Cause Androgen Resistance as Recorded in the Database.
|28 ||Structural Defects ||Different Mutants |
| ||Complete gene deletions ||3 |
| ||Partial gene deletions ||9 |
| ||1–4-bp deletions ||9 |
| ||Intron deletions ||1 |
| ||Splice-junction deletion ||1 |
| ||Insertions ||4 |
| ||Bp duplications ||1 |
| 245 || Single-Base Mutations || Different Mutants |
| ||Amino acid subsitutions ||218 |
| ||Multiple amino acid subtitution ||3 |
| ||Splice-junction abnormalities ||6 |
| ||Premature termination codons ||18 |
| ||TOTAL ||271 |
The large deletions of the androgen receptor gene301 are not shown in Fig. 160-13. Complete deletion of the gene has been described in three families302– 304 ; in the two families in which the deletion extends the farthest, complete testicular feminization is associated with mental retardation.303,304 This finding suggests that a gene that causes mental retardation is located near the androgen receptor gene. In several patients, other large deletions have been characterized.301 In most instances, fibroblasts from these patients do not express androgen receptor that is detectable by assays of hormone binding, but a deletion of exon 3 described by Quigley et al.305 led to the synthesis of a receptor protein that bound hormone but was unable to activate an androgen-responsive gene. Other small-scale deletions that remove single or multiple nucleotides can either cause a shift in the translational reading frame and premature termination of the receptor protein (as occurs in the tfm mouse.306– 308) or, if multiples of three nucleotide residues are deleted, maintain the open reading frame. The size (single or multiple nucleotides) and position of these deletions (within the hormone or DNA-binding domains) determine the type of receptor defect (absent ligand binding or detectable ligand binding) in such individuals. Insertions are less common.
Single nucleotide substitutions in either the DNA- or hormone-binding domains can disrupt the primary structure of the androgen receptor in a variety of ways. First, premature termination codons cause the formation of truncated receptors that are defective in hormone or DNA binding or in assays of transcriptional activation. In one instance, a premature termination codon in the N-terminal region was associated with the formation of a small amount of a shorter receptor that was initiated at a downstream methionine309 ; this shorter isoform is formed in all tissues and functions similarly to the longer, more abundant receptor.310,311 Second, single-nucleotide substitutions (or deletions) can cause aberrant splicing of androgen receptor mRNA.301 Third, missense mutations that cause single-amino-acid substitutions in the DNA-binding domain comprise a category of androgen resistance previously termed receptor-positive resistance or normal androgen binding (see Fig. 160-12) in which hormone binding is normal but binding to DNA is impaired.295,296 Fourth, amino acid substitutions in the hormone-binding domain of the receptor can result in the synthesis of androgen receptor that is unable to bind ligand (absent androgen binding) or that exhibits one or more evidences of impaired hormone binding, such as thermal instability or accelerated ligand dissociation; these substitutions cause a spectrum of phenotypic effects and of alterations in assays using reporter genes.312– 315 Fifth, amino acid substitutions can impair dimerization of the receptor.31
The functional categorization of the androgen resistance syndromes on the basis of the binding characteristics in cultured fibroblasts in some instances has predictive value as to the underlying mutations involved (see Fig. 160-12). Namely, the “normal ligand binding” category consists primarily of individuals with mutations of the DNA-binding domain and one individual with a deletion of exon 3.305 Likewise, the “qualitatively abnormal' category largely consists of missense mutations in the androgen-binding domain. There are multiple causes for “undetectable” binding, including gene deletions (large and small), single-amino-acid substitutions in the androgen-binding domain, premature termination codons, and splicing defects. Likewise, the category of “decreased” amount of receptor that is qualitatively normal has several causes, including single-amino-acid substitutions in the hormone-binding domain,299 intronic mutations that result in the formation of small amounts of normal receptor,316,317 and mosaicism in which the mutation of the androgen receptor is assumed to have occurred shortly after fertilization and in which some cells have a normal gene.318 In all cases, however, mutations in the androgen receptor gene cause different phenotypes by interfering with receptor function to different degrees. Mutations that markedly decrease receptor abundance, receptor function, or both result in complete testicular feminization. Mutations that have lesser effects on receptor quantity and function cause the spectrum of disorders from incomplete testicular feminization to the infertile or undervirilized male. It should be noted that in some families with clear-cut androgen resistance, no mutation has been identified in the gene itself or in its flanking sequences.319
In most instances, the phenotypes of patients with identical mutations of the androgen receptor are similar, whereas individuals with generalized resistance to thyroid hormone, in which individuals carry a specific mutation—even from within a single pedigree—commonly exhibit different manifestations.320 This feature suggests that the level of androgen receptor abundance and function is the principal determinant of phenotype in most patients with androgen resistance. This relation is not uniform, however, because in some families patients with androgen resistance have distinctive phenotypes. In the case of mutations that cause quantitative defects in the formation of normal receptor,263 it is logical that small variations in receptor level could influence phenotype (see Fig. 160-11), but in the case of missense mutations, it is not clear how phenotypic variation arises from the same mutation.321 Factors that may affect phenotype could influence the androgen receptor gene itself (e.g., genes that control the level and timing of androgen receptor expression) or could affect the level of testosterone synthesis or metabolism (e.g., level or timing of 5α-reductase expression). Additional studies will have to be performed to distinguish among these possibilities.
An unexpected feature of androgen receptor disorders is the distribution of mutations in the androgen receptor gene. Although premature termination codons and deletions can occur in all segments of the androgen receptor gene, amino acid substitutions are present predominately in the DNA- and hormone-binding domains. Furthermore, the amino acid substitutions in the hormone-binding domain appear to be particularly common in exon 5.321 Namely, almost one-fifth of the amino acid substitutions shown in Fig. 160-13 are present in an area that includes less than 6 percent of the coding sequence of the receptor. Whether this localization occurs because these segments are particularly vital to the formation of a functional receptor or because the DNA encoding these segments is more prone to mutation remains to be determined. The fact that few amino acid substitutions have been identified in the N-terminal portion of the receptor may be due to ascertainment bias in the types of patients who have been studied or to the complex nature of the domains contained in this region. In vitro mutagenesis of the N-terminus has demonstrated that large segments of the region must be removed before function is altered significantly.322– 324
Approximately 40 percent of individuals with androgen resistance have an uninformative family history, and their disorder is presumed to be due to new mutations. Hiort and colleagues325 studied 30 families in which a mutation in the androgen receptor gene was present in only one family member and found that in 22 the mothers and grandmothers were heterozygous carriers, indicating that the mutation in these families had occurred remotely and was passed through several generations before becoming manifest. In the other 8 instances, a de novo mutation was identified, including 3 individuals with somatic mosaicism, indicating that the mutation occurred after the zygote stage. In another study, evidence was obtained for germ-line mosaicism for a mutation of the androgen receptor in the mother of two individuals with the Reifenstein syndrome.326 These findings are in keeping with the concept that new mutations must be frequent in X-linked disorders that impair reproduction.327
Patients with spinobulbar muscular atrophy (Kennedy syndrome), an X-linked disorder characterized by progressive degeneration of anterior motor neurons and the late onset of mild androgen resistance, have large expansions of the polyglutamine repeat sequences in exon 1 (see Chap. 161). Lesser expansions (28 or more glutamines) are associated with a higher incidence of infertility,221 and very short glutamine repeat sequences also may impair receptor function.314
Suspicion of the presence of an androgen receptor disorder can either occur at birth (genital ambiguity or girls with inguinal hernias or palpable testes in the labia) or after the time of expected puberty (primary amenorrhea in women or unexplained undervirilization or infertility in men). It is necessary to separate these disorders from steroid 5α-reductase 2 deficiency (see above) and from defects in testosterone biosynthesis (see Chap. 159). In the adolescent or adult, the diagnosis of complete testicular feminization is straightforward. A phenotypic woman with primary amenorrhea, a 46,XY karyotype, male levels of testosterone, and bilateral testes (abdominal or inguinal) is found to have absence of Müllerian derivatives by ultrasound328 or by computed tomography (CT) of the abdomen.329 However, separation of incomplete testicular feminization in the adolescent or adult from steroid 5α-reductase 2 deficiency (see above), defects in testosterone biosynthesis (see Chap. 159), and mixed gonadal dysgenesis61 can be a diagnostic problem. In each of these disorders, defects in virilization of the external genitalia may be more severe than that of the Wolffian ducts. Mixed gonadal dysgenesis is often diagnosed by chromosomal analysis. Defects in testosterone biosynthesis usually can be excluded by the presence of normal male testosterone levels, but patients with partial deficiencies may have plasma testosterone levels in the normal or near-normal range; such partial defects, however, are accompanied by elevations in the plasma levels of androgen precursors.142 Steroid 5α-reductase 2 deficiency in this age group is usually diagnosed on the basis of measurement of plasma or urinary 5α-reduced steroids (see above). In resolving these issues, careful analysis of the family history, the phenotype, the endocrine profile, and androgen metabolism in cultured fibroblasts may be required (see Table 160-10). Rarely, women with testicular feminization are not diagnosed until late in life.153
Table 160-10: Summary of Androgen Resistance Syndromes |Favorite Table|Download (.pdf) Table 160-10: Summary of Androgen Resistance Syndromes
| || || ||Phenotype |
| || || || |
|Category ||Inheritance ||Horomonal Profile ||Spermatogenesis ||Müllerian Derivatives ||Wolffian Derivatives ||Urogenital Sinus ||External Genitalia ||Breasts |
|Steroid 5α-reductase 2 deficiency ||Autosomal recessive ||Normal male testosterone and estrogen production ||Decreased ||Absent ||Male ||Female ||Female (may virilize at puberty) ||Male |
|Receptor disorders || || || || || || || || |
|Complete testicular feminization ||X-linked recessive ||Increased testosterone and estrogen production (usually) ||Absent ||Absent ||Absent ||Female ||Female ||Female |
|Incomplete testicular feminization ||X-linked recessive ||Increased testosterone and estrogen production (usually) ||Absent ||Absent ||Male ||Female ||Posterior fusion and/or clitoromegaly ||Female |
|Reifenstein syndrome ||X-linked recessive ||Increased testosterone and estrogen production (usually) ||Absent ||Absent ||Male ||Underdeveloped male ||Perineoscrotal hypospadias ||Gynecomastia |
|Undervirlized or infertile men ||X-linked recessive ||Increased testosterone and estrogen production (usually) ||Absent or decreased ||Absent ||Male ||Male ||Male ||Gynecomastia in some |
The diagnosis is a special problem in the neonate and young infant, particularly when the family history is uninformative. A presumptive diagnosis of androgen resistance can be made in neonates in whom plasma LH and/or testosterone levels are elevated.330,331 In most circumstances, a more extensive evaluation is necessary, including evaluation of karyotype, measurement of plasma steroids after stimulation with hCG, evaluation of the genitourinary tract by radiographic or endoscopic procedures, and on occasion, assessment of androgen metabolism in cultured skin fibroblasts.61,332 It is of particular importance to establish the correct diagnosis of incomplete testicular feminization as early as possible so that castration can be performed early enough in life to prevent partial virilization at puberty.
It is disappointing that diagnosis of androgen receptor mutations has not been made easier by the techniques of molecular biology; indeed, the profound heterogeneity of the mutations of the androgen receptor, the size of the protein, and technical problems involving the use of the polymerase chain reaction to amplify DNA segments containing polyglutamine repeat sequences have impeded the development of techniques for the diagnosis of new mutations in clinical laboratories. Even in research laboratories the sequencing is so slow that it is rarely useful for intrauterine diagnosis. However, once the diagnosis of an androgen receptor defect is established in a specific family, three techniques have been used for carrier detection and/or prenatal diagnosis in individuals at risk. First, the diagnosis can be made in subsequent fetuses at risk early in gestation by sequencing the appropriate exon in DNA prepared from chorionic villus sampling or amniotic fluid cells.309,333 Second, in some families it is possible to use an informative HindIII restriction fragment polymorphism for making the prenatal diagnosis even in the absence of knowing the specific mutation.334 Third, the glutamine repeat polymorphism in exon 1 of the gene also can be used for linkage diagnosis.314,335,336
A functional diagnostic test to aid in the diagnosis of androgen resistance would be particularly useful in children of prepubertal age, but the available tests, including measuring the response of sex hormone-binding globulin levels in plasma to the administration of hCG 337 or a nonaromatizable androgen338 and the measurement of sebum production and/or nitrogen balance after the administration of high-dose androgen therapy,339 are both cumbersome and imprecise.
Since no specific therapy is available to circumvent or reverse the abnormal development that takes place during embryogenesis, treatment is directed toward correction of the external genitalia, prevention of complications and adverse secondary effects of the mutations (including psychological support), and appropriate hormone replacement or supplementation when necessary
Surgical correction of hypospadias and creation of neovaginas by medical or surgical means should be undertaken when appropriate but only at the appropriate age. Usually hypospadias is repaired before boys start school so that they can stand upright when urinating. Vaginal repair should be undertaken only when women are ready to lead an active sex life because of the tendency for the vagina to restenose unless it is dilated regularly and can involve surgical or medical procedures.340 Long-term follow-up studies indicate that neovaginas created by medical means (the Frank procedure) are more likely to function normally than those created surgically.341 Women with incomplete testicular feminization may require correction of the deep posterior forchette, and in some, recession of the clitoris is appropriate.
The Psychological Problems.
Undervirilized or infertile men and women with complete testicular feminization, respectively, have unambiguous male and female phenotypes at birth and are raised accordingly. Individuals with incomplete testicular feminization and the Reifenstein syndrome have varying degrees of abnormal external genitalia, and the correct diagnosis usually can be made in the newborn or child. Because gender identity is critical to psychological development and normal mental health, it is mandatory that gender assignment be made as early as possible, preferably at the time of birth in newborns with ambiguous external genitalia. A detailed discussion of the diagnostic procedures and of the various problems encountered in reaching a decision about gender assignment in infants with ambiguous genitalia is given elsewhere.61,332,342 Once gender assignment is made, the central obligation is to perform any indicated surgery as early as feasible to provide the appropriate hormonal environment at expected puberty and to assist affected individuals in adjusting to their inevitable infertility. With appropriate counseling, women with testicular feminization accept their infertility and make successful adoptive mothers. Indeed, such women have a high record of success in many arenas.
The question of exactly how much and when such women should be told about their diagnosis is an unresolved issue. The argument has been advanced that with appropriate education, sufficient information should be provided so that subjects understand the complete pathophysiology of the condition.343,344 One strong argument for complete disclosure is to prevent the worse alternative of learning the diagnosis inadvertently. However, gender and gender identity are considered by society at large and by many individuals to be rigidly polarized, and subjects with intersex conditions are subjected to discrimination and prejudice. Consequently, it is not surprising that some women with testicular feminization have had severe psychiatric problems, including suicidal behavior after being informed of the true diagnosis. Consequently, no matter how desirable complete disclosure may be in the abstract, the decision to disclose should be made on an individual basis, usually only after consultation with family and after the development of an appropriate support network to aid in helping subjects to make appropriate decisions.345 A support group for individuals with androgen resistance and their parents publishes three newsletters a year and provides valuable psychological support; the address is AIS Support Group, 4203 Genesee Ave., #103-436, San Diego CA 92117.
The most serious complication of the undescended testis in testicular feminization is the development of tumors.2,149,346,347 It likely that tumor incidence in patients with this disorder is similar to that in cryptorchidism of other causes. Approximately 1 in 64 undescended testes becomes malignant, and the frequency of tumor is about four times greater in abdominal than in inguinal testes.348 The natural history of the tumors in women with testicular feminization is not entirely clear, but some behave as true malignancies.347 Therefore, it is generally accepted that the testes should be removed in these women. Since these patients undergo a normal pubertal growth spurt and feminize successfully at the time of expected puberty,2,149 and since tumors usually do not develop in cryptorchid testes until after this time,349 it is customary to delay castration until secondary sexual maturation is complete. Carcinoma in situ of the testes has been described in prepubertal children with testicular feminization, but the functional significance of lesions in unclear.350– 352 If, however, hernia repair is indicated in the prepubertal years, or if testes that are located in the inguinal region or the labia majora cause discomfort, some physicians prefer to perform castration at the time of herniorrhaphy. When testes are removed prepubertally, estrogen therapy is required at the appropriate age to ensure normal growth and breast development. If castration is performed after pubescence, menopausal symptoms and other evidence of estrogen withdrawal supervene,2,149 and suitable estrogen replacement is indicated.
Tumors also can develop in intraabdominal testes in women with incomplete testicular feminization.352 The testes in these subjects should be removed prior to the time of expected puberty to prevent disfiguring virilization that can occur when the plasma testosterone level rises. As above, feminization should be induced in such women with estrogens at the appropriate time.
Cryptorchidism is frequent in the Reifenstein syndrome204 and should be corrected surgically. The Reifenstein case material is small, but in other forms of cryptorchidism, development of tumors is rare following successful repair.348
Gynecomastia in Men with Defects of the Androgen Receptor.
Gynecomastia in these disorders is histologically indistinguishable from other forms of estrogen-induced gynecomastia.200 In men with the Reifenstein syndrome204 and in some infertile men212 or undervirilized men,220 gynecomastia develops as a result both of increased estrogen production and of androgen resistance, as in testicular feminization.7,198 The gynecomastia may be disfiguring as well as disturbing. The appropriate therapy is surgical removal. As in normal men who are castrated,23 gynecomastia occasionally can develop following castration of individuals with androgen resistance.353 This is presumably due to the fact that estrogen formation from adrenal precursors continues unabated following removal of the testes.23
Carcinoma of the breast has been described in men with the Reifenstein syndrome,354,355 whereas mutations in the androgen receptor were not detected in 11 breast cancers of men not associated with an androgen resistance syndrome,356 and it is likely that gynecomastia itself rather than the mutation in the androgen receptor is the predisposing factor.357 Nevertheless, the overall risk in men with gynecomastia is believed to be small.358
Appropriate estrogen treatment is indicated in all phenotypic women after removal of the testes2,149,151 ; such therapy supports or promotes breast development and lubrication of the vagina and promotes feminization in general, but it is not clear whether such regimens prevent the development of osteopenia.179 Testosterone (which can be converted to estrogen in peripheral tissues) also has been used for replacement therapy in women with testicular feminization following castration but has no advantage.359
Supplemental androgen has been administered with success in some83 but not all228,262 men with Reifenstein syndrome. In two instances the fact that the function of the mutant androgen receptor in vitro was enhanced by increased levels of androgen was used to predict successful virilization after the administration of supraphysiologic doses of androgen in two patients with amino acid substitutions in the hormone-binding domain.314,360 Positive responses to androgen also have been described in men with missense mutations of the DNA-binding domain.361,362 However, the value of long-term androgen supplementation in this disorder is not clear. In one man with oligospermia associated with a missense mutation of the hormone-binding domain, treatment with a nonaromatizable androgen caused an increase in sperm count from 2.3 to 3.7 to 28 million/ml.363