Human
lecithin:cholesterol acyltransferase (LCAT) plays a key role in the biogenesis of circulating
high-density lipoprotein-cholesterol (HDL-C) and reverse
cholesterol efflux. We investigated the molecular defect in the LCAT gene in a family with low levels of HDL-C. The proband, a 53-year-old woman from Oklahoma City, had a HDL-C level of 0.21 mmol/l. The LCAT activity in the proband was 5 nmol/ml/h and
cholesterol esterification rate was 54.2 nmol/ml/h, consistent with
LCAT deficiency. Analysis of polymerase chain reaction (PCR) amplified subgenomic fragments of LCAT
DNA on
polyacrylamide gels revealed heteroduplex bands in the proband and three other affected individuals in exon 6. DNA sequence analyses of the proband's LCAT gene identified a 2 base pair deletion (TC) (base pairs 4544-4545, corresponding to
amino acid 255) in the heteroduplex allele, thereby converting Pro(260) to a
premature stop codon and a predicted truncated
protein of 260
amino acids. This is approximately 60% of the length of the normal translated
protein. The heterozygous individuals also revealed significant reduction in
apolipoprotein A-1 levels compared with the unaffected family members (n=4). The marked reduction in HDL-C in the proband and sibling suggests a dominant effect of this mutation on HDL-C levels. Furthermore, because the deletion results in a heterozygous allele that can be detected by a simple PCR reaction and
polyacrylamide gel-size fractionation, it may be possible to rapidly screen susceptible individuals for the presence of this mutation.