Lecithin Cholesterol Acyltransferase Deficiency and Fish Eye Disease

ABSTRACT

• Lecithin cholesterol acyltransferase (LCAT) is a plasma enzyme that esterifies free cholesterol present in circulating plasma lipoproteins.

• LCAT deficiency leads to the development of two clinically distinct syndromes: familial LCAT deficiency (FLD) and fish eye disease (FED).

• FLD is characterized by corneal opacities, anemia, and proteinuria that may progress to renal failure. Foam cells and membrane-bound vesicles, which appear to be composed of cholesterol and phospholipid, accumulate in many tissues including the cornea, kidneys, liver, spleen, bone marrow, and arteries. Target cells containing abnormally high amounts of unesterified cholesterol and lecithin are present. Plasma contains high levels of unesterified cholesterol and phospholipids and low concentrations of plasma cholesteryl esters and lysophosphatidylcholine. Plasma triglycerides are normal to increased, low density lipoprotein (LDL) levels are reduced, and high-density lipoprotein (HDL) levels are markedly decreased. The morphology of the lipoproteins is abnormal, with the presence in plasma of multilamellar vesicles, rouleaux, LpX-like particles, discs, and small spherical particles. The diagnosis of FLD is confirmed by a virtual absence of plasma LCAT activity in patients presenting with hypoalphalipoproteinemia, anemia, proteinuria, or renal disease.

• FED is characterized by corneal opacities. The plasma triglyceride levels are normal to increased, and HDL levels are markedly decreased. The diagnosis of FED is confirmed by finding a partial deficiency of LCAT activity in the plasma of patients presenting with corneal opacities and marked hypoalphalipoproteinemia.

• The LCAT gene is organized into six exons interrupted by five introns and is located on the long arm of chromosome 16. Approximately 40 different mutations in the LCAT gene leading to either FLD or FED have been described to date.

• Characterization of FLD and FED patients as well as different LCAT-transgenic and knockout animal models has demonstrated an important role for LCAT in modulating the metabolism of both HDLs and LDLs, as well as the development of atherosclerosis.

LECITHIN CHOLESTEROL ACYLTRANSFERASE

History

The existence of an enzyme that esterifies cholesterol in plasma was first postulated by Sperry et al.¹ Glomset² provided evidence that a plasma enzyme mediated the esterification of plasma cholesterol by a mechanism that involved the transfer of fatty acids from phosphatidylcholine (PC) to free cholesterol (FC), generating cholesteryl esters (CEs) and lysophosphatidylcholine. The enzyme was termed lecithin cholesterol acyltransferase (LCAT).

Glomset et al.³ first proposed a role for LCAT in reverse cholesterol transport, a process by which cholesterol from peripheral cells is transferred to the liver for catabolism. Cellular FC is taken up by high-density lipoprotein (HDL) where it is esterified by LCAT.⁴ The newly generated CEs are packaged in the core of the lipoprotein, resulting in the maturation of discoidal pre-β-HDL to spherical α-HDL.^5,6 Subsequently, the CE may be exchanged for very low density lipoprotein (VLDL)-triglycerides by the cholesteryl ester transfer protein (CETP)^7,8 for transport to the liver. Alternatively, ...