Two common mutations (D9N, N291S) in lipoprotein lipase: a cumulative analysis of their influence on plasma lipids and lipoproteins in men and women

We assessed the effect of two common mutations in the lipoprotein lipase gene (LPL), D9N and N291S, which have been shown to modulate plasma lipids in a wide spectrum of patients. A total of 1114 men and 1 144 women from the Framingham Offspring Study (FOS) were analyzed for these two LPL variants. Subsequently, the association with fasting plasma lipids and risk of coronary artery disease (CHD) was determined. We extended our study by calculating weighed means of lipids and lipoproteins in carriers and non-carriers for these LPL mutations in patients with genetic dyslipidemias, CHD patients and healthy controls. In the FOS sample, the D9N and N291S alleles were associated with lower high-density lipoprotein-cholesterol (HDL-C) (delta = - 0.07 mmol/ 1, p = 0.03) and a trend towards increased triglycerides (delta = 0.25 mmol/ 1, p = 0.07). In women, a trend towards the high triglyceride, low HDL-C phenotype was evident (delta = - 0.02 mmol/1 for HDL-C and delta = 0.14 mmol/l for triglycerides, respectively). Cumulative analysis of other studies of male carriers of the D9N and N291S revealed higher levels of triglycerides (D291N; 2.60(1.85) mmol/l vs. 1.62(1.18) mmol/l: p < 0.0001) (D9N; 1.94 (1.19) mmol/l vs. 1.74(1.17) mmol/l: p < 0.001) and lower HDL-C (N291S; 1.04(0.32) mmol/l vs. 1.15(0.28) mmol/l: p < 0.0001) (D9N; 1.08(0.24) mmol/l vs. 1.16(0.28) mmol/l: p < 0.0001). In females, results differed with higher TG levels (N291S; 1.70(0.99) mmol/l vs. 1.10(0.63) mmol/l: p < 0.001) (D9N; 1.08(0.76) mmol/l vs. 0.96(0.51) mmol/l: p < 0.01) and lower HDL-C levels (N291S; 1.27(0.33) mmol/l vs. 1.51(0.32) mmol/l: p < 0.0001); however, the HDL-C levels for D9N carriers were similar to non-carriers (D9N; 1.52(0.29) mmol/l vs. 1.53(0.35) mmol/l: p = 0.83). Our data provide evidence that common variants of the LPL gene are significant modulators of lipid and lipoprotein levels in both men and women.

A common truncation variant of lipoprotein lipase (Ser447X) confers protection against coronary heart disease: the Framingham Offspring Study

Genetic variation at the lipoprotein lipase (LPL) locus has been shown to influence plasma lipids and to modulate risk of coronary heart disease (CHD). Recently, we found that the most frequent variant at this locus, involving a C-terminal truncation of two amino acids (Ser447X), was associated with both higher LPL activity and high density lipoprotein cholesterol (HDL-C) in patients with CHD. However, the impact of this S447X variant on lipids and CHD in the general population was hitherto unknown. We, therefore, analyzed a total of 1114 men and 1144 women randomly ascertained from the Framingham Offspring Study (FOS) for the presence of this LPL variant. Carrier frequency of the S447X allele was 17%, and in men carrier status was associated with higher total cholesterol (delta = 6.2 mg/dl, p = 0.03). higher HDL-C (delta = 2.3 mg/dl, p = 0.01), and lower triglyceride (TG) levels (delta = -19.4 mg/dl, p = 0.02). Moreover, in men, the S447X allele conferred significant protection against CHD (odds ratio: 0.43; p = 0.04). These effects on lipids and CHD were not seen in women. Our study represents the first report on the impact of this mutation on CHD in men from the general population, and we conclude, therefore, that the S447X variant may confer significant protection against high TG levels, low HDL-C, and premature CHD in these subjects.

The Asn9 variant of lipoprotein lipase is associated with the -93G promoter mutation and an increased risk of coronary artery disease. The Regress Study Group

Two mutations in the lipoprotein lipase (LPL) gene, a T to G transition at position -93 of the proximal promoter region and an Asp9Asn substitution in exon 2, were examined in 762 Dutch males with angiographically-diagnosed coronary artery disease (CAD) and 296 healthy normolipidemic Dutch males. The two mutations exhibited strong linkage disequilibrium (D' = 0.975). A significantly higher proportion of cases (4.86%) than controls (1.37%) carried the -93G/Asn9 allele (p = 0.008). In the combined sample of cases and controls, adjusted mean plasma total cholesterol (TC) levels were significantly higher in -93G/Asn9 carriers (6.20+/-0.13 mmol/l) than in non-carriers (5.93+/-0.03 mmol/l; p = 0.048), while mean high-density lipoprotein cholesterol (HDL-C) levels were lower in carriers (0.88+/-0.03 mmol/l) than in non-carriers (0.98+/-0.01 mmol/l; p = 0.002). There was a trend towards higher triglyceride (TG) levels in carriers (1.96+/-0.14 mmol/l) compared with non-carriers (1.73+/-0.03 mmol/l) (p = 0.08). Additionally, carrier frequencies in tertiles of TC, HDL-C, TG, and LPL activity, suggested an association of the -93G/Asn9 variant with higher TC and TG levels, and with lower HDL-C and LPL activity levels. Logistic regression revealed a significant odds ratio (OR) for the combined -93G/Asn9 genotype in CAD cases relative to controls (OR: 5.36; 95% CI: 1.57-18.24), with age, body mass index (BMI), smoking, and plasma total- and HDL-cholesterol levels included in the model. In conclusion, we show that the LPL Asp9Asn mutation is in non-random association with a T G substitution at position -93 of the proximal promoter region and that the combined -93G/Asn9 genotype predisposes to decreased HDL-C levels and an increased risk of CAD.

Ethnic variation and in vivo effects of the -93t-->g promoter variant in the lipoprotein lipase gene

Recently, a (t-->g) transition at nucleotide -93 in the lipoprotein lipase (LPL) gene promoter has been observed in Caucasians. Here, we have compared the frequency of the -93g carriers in three distinct populations (Caucasians, South African Blacks, and Chinese). The carrier frequency in the Caucasian population was 1.7% (4/232), which was in contrast to the South African Black population, which had a frequency for this allele of 76.4% (123/161) of the individuals tested. This transition was not observed in the Chinese population under study. Near complete linkage disequilibrium between the -93g and the previously described D9N mutation was observed in the Caucasian population but not in South African Blacks. To further assess the ancestral origins of these DNA changes, DNA haplotyping using a CA repeat 5' to these substitutions was performed. The -93t allele was associated with only a few specific dinucleotide repeat sizes. In contrast, the -93g allele occurred on chromosomes with many different repeat lengths. The broad distribution of repeats on -93g carrying chromosomes, their high frequency in the South African Black population, and the conservation of the -93g allele among different species may suggest that the -93g allele is the ancestral allele on which a transition to t and the D9N mutations arose. The very high frequency of the -93g allele distinct from the N9 allele in a cohort of Black South Africans allowed us to specifically assess the phenotypic effects of the -93g allele on lipids. Individuals homozygous for the g allele at -93 showed mildly decreased triglycerides compared with individuals homozygous for the t allele (1.14 +/- 0.66 mmol/L versus 0.82 +/- 0.3; P = .04). Thus, the -93g allele in this cohort is associated with low plasma triglyceride levels.

Premature atherosclerosis in patients with familial chylomicronemia caused by mutations in the lipoprotein lipase gene

BACKGROUND

Patients with lipoprotein lipase deficiency usually present with chylomicronemia in childhood. The syndrome has been considered nonatherogenic primarily because of the low levels of low-density lipoprotein (LDL) cholesterol. We prospectively evaluated patients with lipoprotein lipase deficiency for atherosclerosis.

METHODS

Evidence of carotid, peripheral, and coronary atherosclerosis was sought in four patients (two men and two women) with the phenotype of familial chylomicronemia by clinical examination over a period of 14 to 30 years and by Doppler ultrasonography, B-mode ultrasonography [corrected], and exercise-tolerance testing after the age of 40. Angiography was performed when indicated. Lipoprotein lipase deficiency was assessed in vivo and in vitro by functional assays and DNA-sequence analysis.

RESULTS

All four patients had a profound functional deficiency of lipoprotein lipase with a reduced enzymatic mass due to missense mutations on both alleles of the lipoprotein lipase gene. In all four patients, peripheral or coronary atherosclerosis (or both) was observed before the age of 55. Despite following a low-fat diet in which fat composed 10 to 15 percent of the daily caloric intake, the patients had hypertriglyceridemia (mean [+/- SD] triglyceride level, 2621 +/- 1112 mg per deciliter [29.59 +/- 12.55 mmol per liter]), low plasma levels of high-density lipoprotein cholesterol (17 +/- 7 mg per deciliter [0.43 +/- 0.18 mmol per liter]), and very low levels of LDL cholesterol (28 +/- 16 mg per deciliter [0.72 +/- 0.41 mmol per liter]). Three patients had one risk factor for atherosclerosis, whereas in one male patient, heavy smoking and diabetes were associated with an accelerated course of the disease.

CONCLUSIONS

Premature atherosclerosis can occur in patients with familiar chylomicronemia as a result of mutations in the lipoprotein lipase gene. Defective lipolysis may increase susceptibility to atherosclerosis in humans.

A frequently occurring mutation in the lipoprotein lipase gene (Asn291Ser) results in altered postprandial chylomicron triglyceride and retinyl palmitate response in normolipidemic carriers

An Asn291Ser mutation in exon 6 of the lipoprotein lipase gene (LPL) frequently occurs in Caucasians (2-4%) and results in a partial catalytic defect. Although this mutation may be associated with low HDL cholesterol and elevated triglyceride levels, some carriers are normolipidemic and may have LPL activity in the normal range in the fasting state. To assess in vivo the influence of dietary stress on the function of this mutation, we have performed oral fat load studies on three unrelated normolipidemic Asn291Ser carriers and compared these results to five healthy controls and to a subject with a clear 50% reduction in LPL activity compared with controls. The Asn291Ser carriers exhibited a more pronounced postprandial response compared with non-carriers as evidenced by higher chylomicron triglyceride (TG) and chylomicron retinyl palmitate peaks (P = 0.03 and P = 0.02, respectively). Significantly higher area under response curves were also seen for both chylomicron triglycerides (P = 0.02) and chylomicron retinyl palmitate (P = 0.01) when compared with non-carriers. These results provide further in vivo evidence for the functional effects of this common mutation despite normal fasting lipid levels. These data suggest that even though subjects with this mutation may be normolipidemic in the fasting state, environmental stress such as an oral fat load may unmask the catalytic defect and result in significant disturbances in postprandial chylomicron metabolism.

Alterations in plasma lipoproteins and apolipoproteins before the age of 40 in heterozygotes for lipoprotein lipase deficiency

We have assessed the expression of heterozygosity for lipoprotein lipase (LPL) deficiency by studying a single large French Canadian family comprising 92 persons including 21 carriers of the catalytically defective P207L mutation. Phenotypic changes distinguishing heterozygotes from controls were seen early, before the age of 40 and often before 20 years of age. In the total cohort these changes included an elevation in the mean very low density (VLDL) and intermediate density lipoprotein (IDL) triglyceride (+69%; P = 0.01 and +40%; P = 0.001) and cholesterol (+51%; P = 0.03 and +67%; P = 0.007) and apoB levels but decreased HDL2 and HDL3 cholesterol, (-32%; P = 0.01 and -15%; P = 0.002 respectively). While the lipid compositions of VLDL and IDL were similar between heterozygotes and controls, the low density (LDL) and high density lipoproteins (HDL) of carriers were triglyceride enriched. Heterozygotes also had a markedly lower apoC-III ratio (apoC-III in supernatant/apoC-III in heparin precipitate) (1.46 vs. 3.86 P = 1 x 10(-4)) indicating a substantial enrichment of VLDL and IDL with apoC-III and depletion of HDL apoC-III supporting this ratio as an effective index for efficiency of lipolysis. LpA-I was markedly reduced (0.34 vs. 0.43 P = 1 x 10(-5)) showing that levels of this particle are partly dependent on LPL catalytic activity. Heterozygotes manifest from an early age with a markedly reduced HDL, LpA-I, apoC-III ratio and an increased TC/HDLc ratio which would predict a relatively increased risk of premature coronary artery disease, compared to their normal siblings.

Mutations in the gene for lipoprotein lipase. A cause for low HDL cholesterol levels in individuals heterozygous for familial hypercholesterolemia

Familial hypercholesterolemia (FH) is characterized by elevated plasma concentrations of LDL cholesterol resulting from mutations in the gene for the LDL receptor. Low HDL cholesterol levels are seen frequently in patients both heterozygous and homozygous for mutations in this gene. Suggested mechanisms for reduced HDL levels in FH patients have been altered apolipoprotein A-1 metabolism and elevated cholesteryl ester transfer protein activity, but the molecular basis for hypoalphalipoproteinemia in any of these patients has not yet been identified. We investigated four large families in which individuals were found to be double heterozygotes for both FH and lipoprotein lipase (LPL) deficiency. These double heterozygotes have significantly less HDL cholesterol than persons with FH or LPL heterozygosity alone. In the double heterozygotes, HDL particle composition is not significantly different from FH heterozygotes, suggesting a quantitative rather than qualitative defect in HDL metabolism in these persons. We propose that mutations in the LPL gene may be a cause of low HDL cholesterol levels in some individuals heterozygous for FH.