Lecithin:cholesterol acyltransferase deficiency: Identification of two defective alleles in fibroblast cDNA

Previous mutations associated with lecithin:cholesterol acyltransferase (LCAT) deficiency have been identified using genomic DNA. To facilitate mutation analysis, we used cDNA front cultured fibroblasts which were shown to express LCAT mRNA. Using reverse-transcriptase PCR, LCAT cDNA was obtained thorn a 13-year-old boy with complete LCAT deficiency, characterized by low HDL-C (3 mg/dl), nondetectable initial cholesterol esterification rate, LCAT activity, and minimal LCAT mass (0.16 vs. 5-7.5 μg/ml). Sequencing of LCAT cDNA clones identified two mutations. A novel frame-shift mutation caused by deletion of cytosine at the third nucleotide position of amino acid 168 (exon 5) predicts a disrupted protein catalytic site by converting Ser₁₈₁→Ala and creates a Pvu-II restriction site prior to premature truncation at amino acid 238. A C→T transition results in a substitution of methionine for threonine at amino acid position 321 and creates an Nla-III restriction site on the maternal allele. Expression studies of mutant LCAT cDNA confirmed the virtual absence of LCAT activity in transfected COS-1 cells. The molecular defect in a young male with complete LCAT deficiency has been identified using fibroblast cDNA.