Patients With ApoE3 Deficiency (E2/2, E3/2, and E4/2) Who Manifest With Hyperlipidemia Have Increased Frequency of an Asn 291→Ser Mutation in the Human LPL Gene

Abstract

Approximately 1% to 2% of persons in the general population are homozygous for a lipoprotein receptor-binding defective form of apoE (apoE2/2). However, only a small percentage (2% to 5%) of all apoE2/2 homozygotes develop type III hyperlipoproteinemia. Interaction with other genetic and environmental factors are required for the expression of this lipid abnormality. We sought to investigate the possible role of LPL gene mutations in the development of hyperlipoproteinemia in apoE2/2 homozygotes and in apoE2 heterozygotes. As a first step, we performed DNA sequence analysis of all 10 LPL coding exons in 2 patients with the apoE2/2 genotype who had type III hyperlipoproteinemia and identified a single missense mutation (Asn 291-->Ser) in exon 6 of the LPL gene. The mutation was then found in 5 of 18 patients with type III hyperlipoproteinemia who had the apoE2/2 genotype (allele frequency = 13.9%; P < or = 7.4 x 10(-5)) and 6 of 22 hyperlipidemic E2 heterozygous patients with the apoE3/2 and E4/2 genotype (allele frequency = 13.6%; P = 2.2 x 10(-5)). In contrast, this mutation was found in only 3 of 230 normolipidemic controls (allele frequency = 0.7%). In vitro mutagenesis studies revealed that the Asn 291-->Ser mutant LPL had approximately 60% of LPL catalytic activity and approximately 70% of specific activity compared with wild-type LPL. The heparin-binding affinity of the mutant LPL was not impaired. Our data suggest that the Asn 291-->Ser substitution is likely to be a significant predisposing factor contributing to the expression of different forms of hyperlipidemia when associated with other genetic factors such as the presence of apoE2.

A common substitution (Asn291Ser) in lipoprotein lipase is associated with increased risk of ischemic heart disease.

“…Since then, this substitution has been described in groups of patients with type III hyperlipoproteinemia (14), in patients with familial combined hyperlipidemia (21,22), and in hypertriglyceridemic patients (5). Plasma HDL cholesterol levels have been found to be decreased and triglyceride levels to be increased in probands identified among patients with familial combined hyperlipidemia (21,22).…”

“…Positive controls were kindly provided by Dr. Anne Minnich (Clinical Research Institute, Montreal, Canada). To distinguish heterozygous from homozygous carriers an RsaI restriction enzyme-based mismatch PCR assay was used, as described previously (4,14). As an internal control of restriction enzyme digestion, part of exon 10 of the lipoprotein lipase gene was amplified in the same PCR.…”

Diagnosis and Management of Type I and Type V Hyperlipoproteinemia

“…Recently, apolipoprotein A-was shown to strengthen the interaction between apolipoprotein C-and LPL, suggesting that familial apolipoprotein A-deficiency causes hyperchylomicronemia 41) . There have also been many reports that abnormalities of apolipoprotein E (E2 or E4) are involved in the pathogenesis of type hyperlipoproteinemia 42) . While homozygous LPL deficiency can be easily diagnosed, heterozygous LPL deficiency is difficult to detect, because its phenotype may be very mild type hyperlipoproteinemia alone or completely asymp- …”

The expression of type III hyperlipoproteinemia: involvement of lipolysis genes

“…33 The following mutations or polymorphisms were identified with PCR followed by restriction enzyme analysis as described earlier: the 3238 G4C (Sst-1; rs5128) 34 polymorphism in 3 0 -untranslated region (UTR) of exon 4 of the APOC3 gene, LPL c.27 G4A (D9N; rs1801177), LPL c.1342 C4G (S447X; rs328), 35 LPL c.874 A4G (N291S; rs268), 13 HL c.219 G4A (V73M; rs6078), HL -480 C4T (rs8192701), 36 HL c.1005 A4G (L334F; rs3829462) 37 and HL c.609 C4G (T202T; rs6084) 38 in the LPL and HL genes, respectively. Analysis of both the APOA5 polymorphisms À1131 T4C (SNP3; rs662799) in the APOA5 promoter region and the c.56 G4C (S19W, rs3135506) in exon 3 of the APOA5 gene was as described earlier.…”

“…Mutations in genes involved in lipolytic conversion, such as LPL (lipoprotein lipase), HL (hepatic lipase) and APOC3 have been associated with hyperlipidemia (for reviews, see references 17 -20 ). In addition, Zhang et al 13 observed an increased allele frequency for the LPL N291S mutation in type III HLP patients when compared with the general population. Single nucleotide polymorphisms (SNPs) in the APOA5 gene (11q23) were found to be strongly associated with plasma TG levels.…”