FAMILIAL LECITHIN - CHOLESTEROL ACYLTRANSFERASE DEFICIENCY - MOLECULAR ANALYSIS OF A COMPOUND HETEROZYGOTE - LCAT (ARG(147)-]TRP) AND LCAT (TYR(171)-]STOP)

Lecithin:cholesterol acyltransferase (LCAT) is responsible for the for mation of the majority of plasma cholesteryl esters. Familial LCAT def iciency is associated with corneal opacity, anemia and proteinurea and typically results in renal failure in the 4-5th decade; this syndrome is equally characterized by the quasi-absence of plasma LCAT activity with variable enzyme mass and very low levels of plasma cholesteryl e sters. In this study, we report detailed analyses of plasma lipids and lipoprotein profile in two sisters (CM and ML) presenting classical h omozygous LCAT-deficiency; the younger sibling (CM) had proteinurea fr om an early age whereas the older sister (ML) has never exhibited rena l dysfunction. We investigated the molecular defect in the 45 year-old woman (proband CM) exhibiting all clinical and biochemical features o f familial LCAT deficiency: a plasma cholesterol level of 105 mg/dl, o f which 95% was unesterified, an HDL-cholesterol of 6.5 mg/dl and an a po A-I level of 52 mg/dl. The proband (CM) displayed a plasma choleste rol esterification rate which corresponded to 2% of normal LCAT activi ty; plasma LCAT protein concentration was 0.56 mu g/ml and equivalent to approximately 10% of normal LCAT mass. Analysis by single strand co nformation polymorphism (SSCP) of the PCR products corresponding to ex ons 4 and 5 of the LCAT gene revealed a visible band shift. Sequence a nalyses of exons 4+5 revealed two separate single point mutations: a C -->T transition replacing Arg(147) by Trp and a T-->G transition conve rting Tyr(171) to a stop codon. The presence of these two point mutati ons was confirmed by restriction enzyme analyses: the C-->T transition abolished a MwoI site whereas the T-->G transition created an AvrII s ite. The Arg(147) mutation was associated with a non-secreted protein. The Tyr(171) mutation resulted in formation of a truncated protein la cking the catalytic site. In summary, we have identified an LCAT defic ient patient corresponding to a compound heterozygote for the Arg(147) -->Trp mutation and a new molecular defect involving a Tyr(171)-->Stop mutation in the LCAT gene. (C) 1997 Elsevier Science Ireland Ltd.