Leucine 10 allelic variant in signal peptide of PCSK9 increases the LDL cholesterol-lowering effect of statins in patients with familial hypercholesterolaemia.

BACKGROUND AND AIMS: In the normal population, carriers of an additional leucine residue in a stretch of nine leucines in the signal peptide of PCSK9 (L10) have lower total (TC) and low-density lipoprotein cholesterol (LDL-C) than homozygotes for the wild-type allele (L9/L9). A similar effect was detected in familial hypercholesterolaemia (FH) patients with the p.C681X mutation of LDL-receptor (LDLR). We investigated the effect of L10 variant on basal lipid profile and response to statins in molecularly characterised FH patients. METHODS AND RESULTS: Plasma lipids were determined in 322 FH patients screened for the L9/L10/L11 polymorphism and in a subgroup of 54 patients carrying the same LDLR mutation (p.Q474HfsX63). Plasma lipids were also determined in 42 FH patients carrying the L10 variant and in a parallel group of 42 FH patients, L9/L9 homozygotes, matched for gender, age, type of LDLR gene mutation, as well as for type, dose and duration of statin treatment. In FH patients, no difference in the basal plasma TC and LDL-C levels was observed between carriers of L10 variant (L9/L10+L10/L10) and L9/L9 homozygotes. The same was true in FH patients carrying the p.Q474HfsX63 LDLR mutation. In the subgroups of statin-treated patients, the reduction of TC and LDL-C was greater in carriers of L10 (-34.0% and -42.5%, respectively) than in L9/L9 homozygotes (-27.5% and -34.3%, respectively) (P<0.001). CONCLUSION: The variant L10 of the leucine repeats in PCSK9 signal peptide is to be considered as a factor capable of modulating the lipid-lowering effects of statins in FH.

Severe HDL deficiency due to novel defects in the ABCA1 transporter.

OBJECTIVES: The objective was the identification and functional characterization of mutations in the ABCA1 gene in four patients with severe HDL deficiency. SUBJECTS: Patients were referred to the clinic because of almost complete HDL deficiency. METHODS: The ABCA1 gene was sequenced directly. The analysis of the ABCA1 protein, ABCA1 mRNA and ABCA1-mediated cholesterol efflux was performed in cultured fibroblasts. Intracellular localization of ABCA1 mutants was investigated in transfected HEK293 cells. RESULTS: Two patients were homozygous for mutations in the coding region of the ABCA1 gene, resulting in an amino acid substitution (p.A1046D) and a truncated protein (p.I74YFsX76). The third patient was homozygous for a splice site mutation in intron 35 (c.4773 + 1g>a), resulting in an in-frame deletion of 25 amino acids (del p.D1567_K1591) in ABCA1. These patients had clinical manifestations of accumulation of cholesterol in the reticulo-endothelial system. The fourth patient, with preclinical atherosclerosis, was a compound heterozygote for two missense mutations (p.R587W/p.W1699C). ABCA1-mediated cholesterol efflux was abolished in fibroblasts from patients with p.A1046D and del p.D1567_K1591 mutants and in fibroblasts homozygous for p.R587W. A reduced ABCA1 protein content was observed in these cells, suggesting an increased intracellular degradation. The mutant p.W1699C was largely retained in the endoplasmic reticulum, when expressed in HEK293 cells. CONCLUSIONS: The homozygotes for mutations which abolish ABCA1 function showed overt signs of involvement of the reticulo-endothelial system. This was not the case in the compound heterozygote for missense mutations, suggesting that this patient retains some residual ABCA1 function that reduces cholesterol accumulation in the reticulo-endothelial system.