Molecular basis of fish-eye disease in a patient from Spain: Characterization of a novel mutation in the LCAT gene and lipid analysis of the cornea

The genetic and biochemical basis of fish-eye disease (FED) was investigated in a 63-year-old female proband with low plasma HDL cholesterol. Analyses of corneal and plasma lipids of the proband were consistent with impaired lecithin:cholesterol acyltransferase (LCAT) activity. Free cholesterol and phospholipid levels were elevated relative to control values, whereas cholesteryl ester levels were greatly reduced. Fatty acid compositions of corneal lipids from the proband and control subjects differ from the respective fatty acid compositions of their plasma lipids. This suggests that the metabolic pathways and acyl chain specificities for phospholipid, cholesteryl ester, and triglyceride metabolism within the cornea are distinct from those of plasma. Sequencing of the LCAT gene from the proband revealed a novel mutation at nucleotide 399, corresponding to an Arg ₉₉→Cys substitution. Secretion of LCAT (Arg ₉₉→Cys) by transfected COS-6 cells was ≃50% of that of the wild type, but its specific activity against reassembled HDL was 93% lower than that of wild-type LCAT. The specific activities of wild-type and LCAT (Arg ₉₉→Cys) against LDL were reduced similarly, suggesting that the appearance of the FED phenotype does not require enhanced activity against LDL. Our data support the hypothesis that FED is a partial LCAT deficiency in which poor esterification in specific types of HDL particles may contribute to the appearance of the corneal opacities.