Molecular Characterization of Loss-of-Function Mutations in PCSK9 and Identification of a Compound Heterozygote

Abstract

Elevated levels of circulating low-density lipoprotein cholesterol (LDL-C) play a central role in the development of atherosclerosis. Mutations in proprotein convertase subtilisin/kexin type 9 (PCSK9) that are associated with lower plasma levels of LDL-C confer protection from coronary heart disease. Here, we show that four severe loss-of-function mutations prevent the secretion of PCSK9 by disrupting synthesis or trafficking of the protein. In contrast to recombinant wild-type PCSK9, which was secreted from cells into the medium within 2 hours, the severe loss-of-function mutations in PCSK9 largely abolished PCSK9 secretion. This finding predicted that circulating levels of PCSK9 would be lower in individuals with the loss-of-function mutations. Immunoprecipitation and immunoblotting of plasma for PCSK9 provided direct evidence that the serine protease is present in the circulation and identified the first known individual who has no immunodetectable circulating PCSK9. This healthy, fertile college graduate, who was a compound heterozygote for two inactivating mutations in PCSK9, had a strikingly low plasma level of LDL-C (14 mg/dL). The very low plasma level of LDL-C and apparent good health of this individual demonstrate that PCSK9 plays a major role in determining plasma levels of LDL-C and provides an attractive target for LDL-lowering therapy.

A Novel Loss of Function Mutation of PCSK9 Gene in White Subjects With Low-Plasma Low-Density Lipoprotein Cholesterol

“…The predicted translation product of this mRNA is a short peptide of 81 amino acids devoid of function, which most likely is not produced because of the rapid degradation of the corresponding mRNA (nonsense-mediated mRNA decay) as demonstrated for the nonsense mutation Y142X found in blacks. 26 The plasma levels of LDL-C and apoB in the proband heterozygous for Ala68fsLeu82X was similar to that found in our FHBL patients heterozygous for APOB gene mutations and in APOB"negative" FHBL subjects. However, the analysis of available family members revealed that in the 2 other adult carriers of the mutation (the father and paternal aunt of the proband) the level of plasma LDL-C and apoB were reduced to a much lesser extent as compared with the proband.…”

Mutations and polymorphisms in the proprotein convertase subtilisin kexin 9 (PCSK9) gene in cholesterol metabolism and disease

“…She had no immunodetectable circulating PCSK9. This 32-year-old African American woman with an LDL-C level of only 14 mg/dl, was apparently healthy, fertile, normotensive, with grossly normal hepatic, neuronal, and renal function tests [Zhao et al, 2006;Horton et al, 2007]. In one Sicilian hypobetalipoproteinemia kindred, a deletion in exon 1 (c.202delG) was found, which causes a frameshift in mRNA leading to a premature stop codon (p.A68fsL82X) [Fasano et al, 2007].…”

“…A woman originating from Zimbabwe, homozygote for p.C679X was reported by Hooper et al [2007] with very low LDL-C (15 mg/dl). Furthermore, Zhao et al [2006] reported a compound heterozygote for the p.Y142X mutation and an inframe 3-bp deletion (c.290_292delGCC) that deletes an arginine at codon 97. She had no immunodetectable circulating PCSK9.…”

PCSK9 Inhibitors in Lipid Management of Patients With Diabetes Mellitus and High Cardiovascular Risk: A Review

“…Conversely, loss‐of‐function PCSK9 mutations are associated with lower serum LDL‐C levels, lower lifelong exposure of vascular structures to LDL, and marked reduction of risk of coronary heart disease 27, 28, 29. Moreover, healthy subjects with severe loss of PCSK9 function have been shown to have serum LDL‐C concentrations as low as 14 mg/dL without apparent adverse health effects 28, 30…”