Lipoprotein lipase gene mutations D9N and N291S in four pedigrees with familial combined hyperlipidaemia

Correlation between chylomicronemia diagnosis scores and post-heparin lipoprotein lipase activity

INTRODUCTION

Sustained chylomicronemia is a defect in post-prandial triglyceride management characterized by severe hypertriglyceridemia (triglyceride > 10 mmol/L) due to functional or genetic defects in lipoprotein lipase (LPL)-mediated triglyceride-rich lipoprotein lipolysis. Familial chylomicronemia syndrome (FCS) is a rare mendelian form of chylomicronemia caused by loss-of-function variants in LPL or LPL-related genes. Most individuals with chylomicronemia however present multifactorial chylomicronemia (MCS), in which LPL bio-availability and activity are variable. FCS and MCS differ in terms of clinical characteristics and risk of disease, and diagnosis scoring systems have been proposed to accurately distinguish FCS from MCS.

OBJECTIVE

The aim of this study was to assess the strength of the relationship between plasma post-heparin LPL activity and two published chylomicronemia diagnosis scoring systems.

DESIGN AND METHODS

Post-heparin plasma LPL activity was measured using colorimetric assays in a sample of 29 subjects with sustained chylomicronemia (20 FCS and 9 MCS). Chylomicronemia diagnosis scores were obtained for all subjects using the scoring system A (model A), which integrates apolipoprotein B and free glycerol, a surrogate marker of triglyceride hydrolysis, and the scoring system B (model B). Correlation analyses were conducted to estimate the linear relationship between LPL activity and the two diagnosis scoring systems.

RESULTS

There was a significant (p < 0.001) difference in post-heparin LPL activity between FCS and MCS. Both scoring systems significantly correlated with post-heparin LPL activity (model A: r_s = -0.64, p < 0.001; model B: r_s = -0.54, p = 0.002).

CONCLUSIONS

These result suggest that chylomicronemia diagnosis scoring systems correlate with LPL activity and adequately contribute to distinguish FCS from MCS.

Atorvastatin-associated rhabdomyolysis in a patient with a novel variant of the SLCO1B1 gene: A case report

We report the case of an individual with severe hypercholesterolemia who experienced rhabdomyolysis with high dose atorvastatin. Genetic testing was undertaken to evaluate for suspected familial hypercholesterolemia (FH) and for the presence of gene variants associated with susceptibility to statin associated muscle disease. Genetic testing identified the presence of a potentially damaging variant of the hepatic xenobiotic transporter pump SLCO1B1, a single nucleotide variant (SNV) (rs77271279, c.481+1G>T) that disrupts the canonical donor splice motif. Although this variant has not previously been reported as associated with rhabdomyolysis and thus requires validation in population studies, it likely played a role in this patient's susceptibility to rhabdomyolysis based on functional assessment of the effect of this variant on SLCO1B1 protein function and given the known role of this transporter in statin uptake by the liver. The presence of this gene variant reinforced our decision to treat the patient's hypercholesterolemia with non-statin alternatives (PCSK9 inhibitor and ezetimibe). Genetic testing also identified the presence of a second SLCO1B1 gene variant, c.1200C>G (p.Phe400Leu, rs59113707) and homozygosity for an intron variant of the apolipoprotein(a) (LPA) gene (c.2604.138G>A intron variant, rs9457951) associated with increased Lp(a), a risk factor for atherosclerotic cardiovascular disease. Notably, all three variants are rare in persons of European descent but more frequent in African-Americans. These findings underscore the role of disabling mutations of the SLCO1B1 gene in statin myopathy and the need to validate these and other gene variants associated with statin myopathy in a population of patients with statin-associated muscle disease.

Association of common gene-smoking interactions with elevated plasma apolipoprotein B concentration

Background

Increased apolipoprotein (apo) B level (hyperapoB) is a strong predictor of cardiovascular disease (CVD), even in patients who achieve recommended LDL-Cholesterol (LDL-C) goals. ApoB level, an important correlate of metabolic syndrome (MetS), is influenced by several gene-environment interactions. Some of them are rare and can explain a large proportion of apoB variance, whereas others more common have variable effects. The aim of this study was to evaluate the association of interaction between smoking and common hyperapoB gene variants (PPARα-L162V, lipoprotein lipase loss-of function mutation, apo e4 allele or apo E2/2 genotype) with plasma apoB concentrations, according to the expression of MetS.

Methods

This study was performed among 1798 subjects. Smoking was defined as non/mild smokers vs. moderate-to-heavy smokers. ApoB levels were determined using nephelometry. Logistic regression models were used to document interactions between smoking habits and the presence of hyperapoB gene variants on the relative odds to exhibit increased plasma apoB concentrations.

Results

Around 29% of individuals with a low-risk lipid profile without MetS component had hyperapoB. Smoking and the presence of hyperapoB gene variants tended to be associated with higher plasma apoB levels even in presence of low-LDL-C. There was a significant interaction (P = 0.04) between the presence of ≥1 gene variants and smoking on the risk to exhibit hyperapoB among subjects with low risk profile in primary prevention.

Conclusions

Combination of life habits assessment and some common genes variants may detect a significant proportion of patients with increased apoB levels, and therefore a higher risk of CVD, who could have been initially perceived as low-risk.

Genetic analysis of familial hypercholesterolemia in Asian Indians: A single-center study

BACKGROUND

Familial hypercholesterolemia (FH), an autosomal codominant disorder characterized by very high low-density lipoprotein cholesterol, is strongly associated with premature coronary artery disease.

OBJECTIVES

Molecular landscape of FH in Asian Indians is not well studied, although this ethnic group comprises a large proportion of the world population. Knowledge of mutations in these groups is useful for identifying persons affected with FH, saving their lives, and cascade screening in their relatives.

METHODS

Potential cases of FH (n = 100) were identified by criteria adapted for the Indian population from Dutch Lipid Clinic Network criteria. Pathogenic variants were analyzed in LDLR, APOB 100 (exons 26 and 29), PCSK9, and APOE genes using Sanger sequencing and multiplex ligation-dependent probe amplification technique. Cases in whom there were no pathogenic variants were tested by next-generation sequencing using a targeted panel of genes.

RESULTS

Thirty-eight pathogenic variants were identified in 47 of 100 unrelated probands. Of these variants, 33 were identified in LDLR, 3 in APOB, and 2 in PCSK9 genes. Ten pathogenic variants were novel. Mutations were detected in 91.4% of those subjects classified as definite, 40% as probable, and in 18.8% as possible FH cases based on modified Dutch Lipid Clinic Network criteria. A likely founder mutation in intron 10 (c.1587-1G>A) of LDLR gene was observed in 6 North Indian families. The conventional pathogenic variants in APOB and PCSK9 genes and those previously reported in LDLR gene among Asian Indians were not detected in this cohort.

CONCLUSION

This study demonstrates genetic heterogeneity of FH in India. The variants observed were different from those described in Western populations. Next-generation sequencing technology helped identify new mutations in APOB gene, suggesting that in less-studied populations, it is better to sequence the whole gene rather than test for specific mutations.

Genetic determinants of inherited susceptibility to hypercholesterolemia - a comprehensive literature review

Hypercholesterolemia is a strong determinant of mortality and morbidity associated with cardiovascular diseases and a major contributor to the global disease burden. Mutations in four genes (LDLR, APOB, PCSK9 and LDLRAP1) account for the majority of cases with familial hypercholesterolemia. However, a substantial proportion of adults with hypercholesterolemia do not have a mutation in any of these four genes. This indicates the probability of having other genes with a causative or contributory role in the pathogenesis of hypercholesterolemia and suggests a polygenic inheritance of this condition. Here in, we review the recent evidence of association of the genetic variants with hypercholesterolemia and the three lipid traits; total cholesterol (TC), HDL-cholesterol (HDL-C) and LDL-cholesterol (LDL-C), their biological pathways and the associated pathogenetic mechanisms. Nearly 80 genes involved in lipid metabolism (encoding structural components of lipoproteins, lipoprotein receptors and related proteins, enzymes, lipid transporters, lipid transfer proteins, and activators or inhibitors of protein function and gene transcription) with single nucleotide variants (SNVs) that are recognized to be associated with hypercholesterolemia and serum lipid traits in genome-wide association studies and candidate gene studies were identified. In addition, genome-wide association studies in different populations have identified SNVs associated with TC, HDL-C and LDL-C in nearly 120 genes within or in the vicinity of the genes that are not known to be involved in lipid metabolism. Over 90% of the SNVs in both these groups are located outside the coding regions of the genes. These findings indicates that there might be a considerable number of unrecognized processes and mechanisms of lipid homeostasis, which when disrupted, would lead to hypercholesterolemia. Knowledge of these molecular pathways will enable the discovery of novel treatment and preventive methods as well as identify the biochemical and molecular markers for the risk prediction and early detection of this common, yet potentially debilitating condition.

The D9N, N291S, and T495G Polymorphisms of the Lipoprotein Lipase Gene Are Not Associated with Cerebral Infarction

BACKGROUND

Lipoprotein lipase (LPL) plays an important role in plasma lipoprotein metabolism and its polymorphisms are possibly implicated in the etiology of ischemic cerebrovascular disease (CVD). The aim of this work was to determine the association of the of D9N, N291S, and T495G polymorphisms of the LPL gene as a risk factor for the development of CVD.

METHODS

A case-control study was conducted that included 100 patients with CVD and 120 healthy controls. All the subjects were genotyped for the D9N, N291S, and T495G polymorphisms of the LPL gene through polymerase chain reaction-restriction fragment length polymorphism, and the results were analyzed for their association with CVD.

RESULTS

The D9N genotype was not significantly correlated with CVD; the odds ratio (OR) between the control subjects and CVD patients was .29 (95% confidence interval [CI], .03-2.66; P = .27). The N291S polymorphism was not significantly correlated with CVD either; the OR between the control subjects and CVD patients was 1.2 (95% CI, .07-19.46; P = .89). And the T495G mutation was not significantly correlated with CVD; the OR between the control subjects and the CVD patients was 1.21 (95% CI, .7-2.08; P = .48).

CONCLUSIONS

In the present study, the D9N, N291S, and T495G polymorphisms of the LPL gene were not risk factors for the development of CVD.

Atherogenic dyslipidemia in children: evaluation of clinical, biochemical and genetic aspects

The precursors of atherogenic dyslipidemia (AD) are not well defined. Therefore, we investigated 62 non-obese, non-diabetic AD and 221 normolipemic children. Anthropometric parameters, blood pressure and biochemical measures were obtained in index children, their parents and all available siblings. The heritability (h²) of anthropometric and biochemical traits was estimated by SOLAR. Rare and common variants in APOA1 and LPL genes were screened by re-sequencing. Compared to normolipemic, AD children showed increased body mass index, waist circumference, plasma glucose, insulin, ApoB, HOMA-IR, hs-CRP and lower adiponectin (p<0.001 for all). Metabolic syndrome was present in 40% of AD while absent in controls. All traits (except adiponectin and hs-CRP) showed a strong familial aggregation, with plasma glucose having the highest heritability (89%). Overall, 4 LPL loss-of-function mutations were detected (p.Asp9Asn, p.Ser45Asn, p.Asn291Ser, p.Leu365Val) and their cumulative prevalence was higher in AD than in control children (0.073 vs. 0.026; P=0.038). The LPL p.S447* gain-of-function mutation, resulted to be less frequent in AD than in control children (0.064 vs. 0.126; P=0.082). No variant in the APOA1 gene was found. Our data indicate that AD is a rather common dyslipidemia in childhood; it associates with metabolic abnormalities typical of insulin resistant state and shows a strong familial aggregation. LPL variants may contribute to the development of AD phenotype.

The g.-469G>A polymorphism in the GPIHBP1 gene promoter is associated with hypertriglyceridemia and has an additive effect on the risk conferred by LPL defective alleles

BACKGROUND AND AIMS

Hypertriglyceridemia (hyperTG) is a component of the metabolic syndrome and a cardiovascular or pancreatitis risk factor. Although both genetic and environmental factors influence its expression, the biological component of hyperTG is still underestimated and has been reported in 10-20% of cases only. Given its key role in the lipolysis of TG-rich lipoproteins, glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1 (GPIHBP1) is a biological candidate for hyperTG. The aim of this study was to assess the association of new GPIHBP1 gene variants with hyperTG (fasting plasma TG values ≥ 2.0 mmol/L).

METHODS AND RESULTS

Sequencing the GPIHBP1 gene identified a g.-469G > A (rs72691625) polymorphism in the promoter. A sample of 541 Caucasians (263 normoTG and 278 hyperTG) was then screened for this polymorphism using a 5'nuclease TaqMan. In multivariate analyses, GPIHBP1 g.-469G > A polymorphism carriers were at significantly higher risk of hyperTG (≥ 2.0 mmol/L) than non-carriers, the odds ratio (OR) being 1.67 (p = 0.025) among heterozygotes and 5.70 (p = 0.004) in homozygotes. The simultaneous presence of loss-of-function LPL polymorphisms had an incremental additive effect on the risk of hyperTG (OR: 7.30; p < 0.001), highlighting the importance of gene-gene interactions in the expression of hyperTG.

CONCLUSIONS

In this study, the g.-469G >A polymorphism in the GPIHBP1 gene promoter was associated with an increased risk of hyperTG and had an additive effect on the risk conferred by LPL defective alleles.

The genetics of familial combined hyperlipidaemia

Almost 40 years after the first description of familial combined hyperlipidaemia (FCHL) as a discrete entity, the genetic and metabolic basis of this prevalent disease has yet to be fully unveiled. In general, two strategies have been applied to elucidate its complex genetic background, the candidate-gene and the linkage approach, which have yielded an extensive list of genes associated with FCHL or its related traits, with a variable degree of scientific evidence. Some genes influence the FCHL phenotype in many pedigrees, whereas others are responsible for the affected state in only one kindred, thereby adding to the genetic and phenotypic heterogeneity of FCHL. This Review outlines the individual genes that have been described in FCHL and how these genes can be incorporated into the current concept of metabolic pathways resulting in FCHL: adipose tissue dysfunction, hepatic fat accumulation and overproduction, disturbed metabolism and delayed clearance of apolipoprotein-B-containing particles. Genes that affect metabolism and clearance of plasma lipoprotein particles have been most thoroughly studied. The adoption of new traits, in addition to the classic plasma lipid traits, could aid in the identification of new genes implicated in other pathways in FCHL. Moreover, systems genetic analysis, which integrates genetic polymorphisms with data on gene expression levels, lipidomics or metabolomics, will attribute functions to genetic variants in addition to revealing new genes.

Apolipoprotein E and lipoprotein lipase gene polymorphisms interaction on the atherogenic combined expression of hypertriglyceridemia and hyperapobetalipoproteinemia phenotypes

The combination of hypertriglyceridemia (hyperTG) and hyperapobetalipoproteinemia (hyperapoB) is associated with an increased coronary artery disease (CAD) risk. Apolipoprotein (apo) E and lipoprotein lipase (LPL) genes are involved in the catabolism of triglycerides (TG)-rich apoB-containing lipoproteins (VLDL). Several apoE and LPL gene variants affecting CAD risk, plasma TG or apoB concentrations have an allelic frequency of >5% in the general population. This study examined the combined effect of frequent apoE and LPL gene polymorphisms on the expression of hyperTG and hyperapoB. ApoE (E2, E3, and E4) and LPL (D9N, N291S, G188E, and P207L) were genotyped and fasting lipid profiles were assessed among 1,441 French-Canadian subjects. Multivariate analyses were performed to estimate the relationship between apoE and LPL gene variants and the risk of hyperTG (TG>1.7 mmol/l) and hyperapoB (apoB>0.9 g/l). Compared to apoE3 carriers, the apoE4 allele significantly increased the risk of expressing the "hyperTG/hyperapoB" phenotype [odds ratio (OR)=1.95; p=0.014]. This risk was significantly exacerbated (OR=4.69; p=0.017) by the presence of frequent deleterious LPL gene variants in this population. The apoE2 allele was negatively associated with hyperTG/hyperapoB (OR=0.49; p=0.002) in the absence of a deleterious LPL gene variant. These results suggest that epistasis is a phenomenon to consider while assessing the CAD risk associated with gene variants or the effect of frequent alleles on high-risk lipid profiles.

Genetic epistasis in the VLDL catabolic pathway is associated with deleterious variations on triglyceridemia in obese subjects

BACKGROUND

Abdominal obesity and hypertriglyceridemia (the hypertriglyceridemic-waist phenotype) increase cardiovascular risk. The very low-density lipoprotein (VLDL) is a triglyceride (TG)-rich particle. Frequent variations in the genes coding for enzymes and proteins involved in the VLDL catabolism have already been documented. The epistatic effect of such variants on the risk profile associated with abdominal obesity remains to be elucidated.

OBJECTIVE

This study aims to assess the effect of combinations of frequent single-nucleotide polymorphisms (SNPs) in the VLDL catabolic pathway on the relation between abdominal obesity and fasting TG.

METHOD

Only gene variants in the lipoprotein lipase, apolipoprotein (apo) CIII, hepatic lipase and apo E genes known to be frequent in the general population (allele frequency>5%) were included in this study. The presence of selected SNPs was detected by polymerase chain reaction-restriction fragment length polymorphism in a sample of 640 non-diabetic French Canadians at high cardiovascular risk (405 obese, 235 non-obese).

RESULTS

Carrying more than two frequent gene variants involved in the VLDL catabolic pathway significantly increased the risk of hyperTG (odds ratio of TG>1.7 mmol/l=4.15; P=0.001). This effect was proportional to the number of SNPs and genes involved and was significantly amplified by the presence of abdominal obesity defined on the basis of waist circumference.

CONCLUSION

When combined with abdominal obesity, epistasis in the VLDL pathway has a deleterious effect on fasting TG and coronary artery disease risk profile according to the TG threshold (1.7 mmol/l) used in medical guidelines for the assessment of the metabolic syndrome and associated risk.

The lipoprotein lipase gene in combined hyperlipidemia: evidence of a protective allele depletion

Background

Lipoprotein Lipase (LPL), a key enzyme in lipid metabolism, catalyzes the hydrolysis of triglycerides (TG) from TG-rich lipoproteins, and serves a bridging function that enhances the cellular uptake of lipoproteins. Abnormalities in LPL function are associated with pathophysiological conditions, including familial combined hyperlipidemia (FCH). Whereas two LPL susceptibility alleles were found to co-segregate in a few FCH kindred, a role for common, protective alleles remains unexplored. The LPL Ser447Stop (S447X) allele is associated with anti-atherogenic lipid profiles and a modest reduction in risk for coronary disease. We hypothesize that significant depletion of the 447X allele exists in combined hyperlipidemia cases versus controls. A case-control design was employed. The polymorphism was assessed by restriction assay in 212 cases and 161 controls. Genotypic, allelic, and phenotypic associations were examined.

Results

We found evidence of significant allelic (447X_control: 0.130 vs. 447X_case: 0.031, χ² = 29.085; 1df; p < 0.001) and genotypic association (SS: 0.745 vs. 0.939, and SX+XX: 0.255 vs. 0.061) in controls and cases, respectively (χ² = 26.09; 1df; p < 0.001). In cases, depletion of the 447X allele is associated with a significant elevation in very-low-density lipoprotein cholesterol (VLDL-C, p = 0.045). Consonant with previous studies of this polymorphism, regression models predict that carriers of the 447X allele displayed significantly lower TG, low-density lipoprotein cholesterol (LDL-C) and TG/high-density lipoprotein cholesterol (HDL-C) ratio.

Conclusion

These findings suggest a role for the S447X polymorphism in combined hyperlipidemia and demonstrate the importance of evaluating both susceptibility and protective genetic risk factors.

Unraveling the complex genetics of familial combined hyperlipidemia

Familial combined hyperlipidemia (FCHL) constitutes a substantial risk factor for atherosclerosis since it is observed in about 20% of coronary heart disease (CHD) patients under 60 years. FCHL, characterized by elevated levels of total cholesterol (TC) and triglycerides (TGs), or both, is also one of the most common familial hyperlipidemias with a prevalence of 1%-6% in Western populations. Numerous studies have been performed to identify genes contributing to FCHL. The recent linkage and association studies and their replications are beginning to elucidate the genetic variations underlying the susceptibility to FCHL. Three chromosomal regions on 1q21-23, 11p and 16q22-24.1 have been replicated in different study samples, offering targets for gene hunting. In addition, several candidate gene studies have replicated the influence of the lipoprotein lipase (LPL) gene and apolipoprotein A1/C3/A4/A5 (APOA1/C3/A4/A5) gene cluster in FCHL. Recently, the linked region on chromosome 1q21 was successfully fine-mapped and the upstream transcription factor 1 (USF1) gene identified as the underlying gene for FCHL. This finding has now been replicated in independent FCHL samples. However, the total number of variants, the risk related to each variant and their relative contributions to the disease susceptibility are not known yet.

Lipoprotein Lipase Gene is Linked and Associated with Hypertension in Taiwan Young-onset Hypertension Genetic Study

Hypertriglyceridemia has been extensively associated with hypertension. However, the mechanism behind it is poorly understood. A positive linkage signal between Lipoprotein lipase (LPL) and young-onset hypertension has been identified by us as the strongest among 18 candidate genes. Here we report our fine mapping works with seven microsatellite markers flanking LPL, sequencing results for its promoter and exons, and an extended association study with the identified single nucleotide polymorphisms(SNP). First, using data from 213 individuals in 59 nuclear families of young-onset hypertension, multipoint analysis revealed a NPL score of 3.02 for the LPL (GZ-14/GZ-15) marker in intron 6. LPL marker (p < 10(-12)) and the haplotypes containing its allele 1 (p < 0.0001) were also significantly associated with young hypertension by transmission disequilibrium test. In-depth sequencing revealed no mutation in promoter and exon regions, except two cSNP: 7754C--> A (C/A: 0.91/0.09), a silent mutation in exon 8 and S447X (C/G: 0.92/0.08), a stop codon mutation in exon 9. Other 11 cSNPs documented in NCBI GenBank are absent in our sample. Constructed from the above 2 cSNPs, haplotype AC showed a moderate TDT association with elevated triglyceride (p = 0.02) and with hypertension and elevated triglyceride combined (p = 0.06). Again, in an extended case-control study, a significant association was found between S447X and patients with persistent hypertension and elevated triglyceride (p = 0.02). We conclude that LPL variants may play a causal role in the development of hypertension in Taiwan Han Chinese. The moderate association with SNP haplotype suggests that other regulatory LPL variant may exist.

Effect of the APOC3 Sst I SNP on fasting triglyceride levels in men heterozygous for the LPL P207L deficiency

Lipoprotein lipase (LPL) plays a major role in triglyceride (TG)-rich lipoprotein catabolism. A mutation at codon 207 (P207L) in the exon 5 of the LPL gene has been associated with 50% reduction in postheparin plasma LPL activity and significant increase in plasma TG levels in heterozygous individuals with low HDL. However, heterogeneity in fasting TG concentrations among these carriers suggests that other factors may be involved in the expression of this hypertriglyceridemic state. Indeed, previous studies have shown that the rare S2 allele of the APOC3 Sst I polymorphism was associated with higher concentrations of TG levels in noncarriers of LPL defect. Therefore, we investigated the association of the APOC3 Sst I variant on fasting lipoprotein-lipid levels in a sample of 35 heterozygous men bearing the LPL P207L mutation. Genetic association analyses were performed using the two-genotype groups S1/S1 and S1/S2. The genotype S1/S2 group was characterized by greater plasma cholesterol (plasma-C, P=0.02), plasma-TG (P=0.04), very low-density lipoproteins (VLDL)-C (P=0.004), VLDL-TG (P=0.01), VLDL-apolipoprotein B (apoB) (P=0.001) levels and cholesterol/HDL-C ratio (P=0.008), as well as lower VLDL-TG/VLDL-apoB ratio compared to the S1/S1 genotype group. These results support an exacerbating effect of the APOC3 Sst I single-nucleotide polymorphism on fasting TG levels since a large number of smaller VLDL particles are observed in LPL-deficient men bearing the APOC3 S2 allele.

Effects of atorvastatin on the clearance of triglyceride-rich lipoproteins in familial combined hyperlipidemia

Familial combined hyperlipidemia (FCHL) patients have an impaired catabolism of postprandial triglyceride (TG)-rich lipoproteins (TRLs). We investigated whether atorvastatin corrects the delayed clearance of large TRLs in FCHL by evaluating the acute clearance of Intralipid (10%) and TRLs after oral fat-loading tests. Sixteen matched controls were included. Atorvastatin reduced fasting plasma TG (from 3.6 +/- 0.4 to 2.5 +/- 0.3 mM; mean +/- SEM) without major effects on fasting apolipoprotein B48 (apoB48) and apoB100 in large TRLs. Atorvastatin significantly reduced fasting intermediate density lipoprotein (Svedberg flotation, 12-20)-apoB100 concentrations. After Intralipid, TG in plasma and TRL showed similar kinetics in FCHL before and after atorvastatin treatment, although compared with controls, the clearance of large TRLs was only significantly slower in untreated FCHL, suggesting an improvement by atorvastatin. Investigated with oral fat-loading tests, the clearance of very low density lipoprotein (Sf20-60)-apoB100 improved by 24%, without major changes in the other fractions. The most striking effects of atorvastatin on postprandial lipemia in FCHL were on hepatic TRL, without major improvements on intestinal TRLs. Fasting plasma TG should be reduced more aggressively in FCHL to overcome the lipolytic disturbance causing delayed clearance of postprandial TRLs.

Lipoprotein distribution in the metabolic syndrome, type 2 diabetes mellitus, and familial combined hyperlipidemia

Metabolic abnormalities associated with the metabolic syndrome are also present in patients with type 2 diabetes mellitus and in those with familial combined hyperlipidemia (FCHL). These abnormalities include central obesity, insulin resistance with hyperinsulinemia, hypertension, increased plasma triglycerides, and decreased high-density lipoprotein cholesterol levels. Other characteristics associated with FCHL include the presence of small, dense low-density lipoprotein cholesterol and increased apolipoprotein B. Patients with these abnormalities are at an increased risk for premature coronary artery disease. Treatment of the dyslipidemia associated with type 2 diabetes and FCHL with a combination of a statin and a thiazolidinedione or niacin offers the most comprehensive modality to correct the various lipid abnormalities.

Postprandial triglyceride levels in familial combined hyperlipidemia. The role of apolipoprotein E and lipoprotein lipase polymorphisms

The effect of apolipoprotein E genotype and polymorphisms of lipoprotein lipase gene on plasma postprandial triglyceride levels in familial combined hyperlipidemic subjects and their relatives have not been sufficiently studied. This study included sixteen familial combined hyperlipidemic parents (G1): age: 52 +/- 9 years with total-cholesterol: 7.2 +/- 1.7 mmol/L, fasting triglycerides: 2.8 +/- 1.4 mmol/L and sixteen children (G2) (twelve were normolipidemic): of age: 22 +/- 5 years with total-cholesterol: 5.2 +/- 1.1 mmol/L, fasting triglycerides: 2.06 +/- 1.8 mmol/L and twelve normolipidemic, healthy controls. Blood samples were taken fasting and 2, 4, 6, 8, 10 hr postprandially after the standard fat rich test meal. We determined lipid parameters, apolipoprotein E and lipoprotein lipase HindIII and PvuII polymorphisms as well. The 6-hr critical postprandial triglyceride values were abnormal in both G1: 5.88 +/- 2.7 mmol/L and G2: 3.53 +/- 2.7 mmol/L (p <0.001), respectively, and differed significantly (p <0.001) from each other. The subjects of familial combined hyperlipidemic families with E4 allele in both generations exhibited significantly (p <0.001) higher and extended postprandial lipemia. We did not find significant effects of lipoprotein lipase HindIII or PvuII polymorphisms on the fasting lipid values alone, however in normolipidemic subjects from the same families the homozygosity of HindIII variation was associated with higher triglyceride postprandial peak (p <0.01). The main findings of our study are that i.) normolipidemic G2 subjects in familial combined hyperlipidemic families have already abnormal postprandial status, and ii.) the 6 h postprandial triglyceride values were correlated with fasting triglyceride levels, which showed association with the apolipoprotein E4 allele.

Effect of apolipoprotein E, peroxisome proliferator-activated receptor alpha and lipoprotein lipase gene mutations on the ability of fenofibrate to improve lipid profiles and reach clinical guideline targets among hypertriglyceridemic patients

Fenofibrate is a peroxisome proliferator-activated receptor alpha (PPARalpha) agonist which regulates the transcription of genes encoding proteins involved in triglyceride (TG)-rich lipoproteins and lipoprotein lipase (LPL) metabolism. The aim of the present study was to investigate the relation between TG-related parameters considered in different clinical guidelines used in industrialized countries for the management of lipid disorders (namely fasting plasma TG, high density-lipoprotein cholesterol (HDL-C), non-HDL-C concentrations and total-C/HDL-C ratio) and the presence of LPL-null (P207L), LPL-defective (D9N), PPARalpha -L162V, apolipoprotein (apo) E and PPARgamma-P12A gene mutations, in a sample of 292 hypertriglyceridemic subjects treated with fenofibrate for 3 months. Although fenofibrate induced a decrease in plasma TG level and an increase in HDL-C level in all studied genotypes, mutation-specific differences were observed. After adjustment for age, gender, body mass index and the presence of apo E2 genotype, the LPL-P207L mutation was associated with residual post-treatment hypertriglyceridemia [TG > 2.0 mmol/l, odds ratio (OR) = 3.07, P = 0.005] and total-C/HDL-C ratio > 5 (OR = 2.68; P = 0.03). This effect was significantly related to higher plasma TG concentrations at baseline among carriers of a LPL-null mutation. Compared to apo E3 and E4 variants, the apo E2 allele was associated with a better response to fenofibrate on all lipid parameter, especially among PPARalpha -L162V carriers, whereas the simultaneous presence of apo E2 and PPARalpha -L162V tended to improve fenofibrate response among LPL-P207L heterozygotes. Finally, the LPL-D9N and PPARgamma -P12A mutations did not affect fenofibrate lipid-lowering action. This study suggests that frequent genetic variations in genes encoding proteins involved in TG-rich lipoprotein metabolism could modulate the response to fenofibrate treatment, as defined in clinical guidelines.

Calibration, specificity and trueness of a postheparin plasma lipoprotein lipase assay

Measurement of lipoprotein lipase activity in postheparin plasma is generally accompanied by moderate within-run variation CV(W-R) (<10%) and higher between-run variation CV(B-R) (5-25%). A calibration system was introduced in order to improve the reproducibility of measurements and to compare lipoprotein lipase activities from different days. Every day a calibration curve for lipoprotein lipase activity was constructed. Fifteen calibration curves designed over 2 years, show linearity over the whole biological spectrum and a considerable reduction of between-run variation in lipoprotein lipase activity, from 42% to 5.3% as estimated from two control postheparin plasma samples. The lipoprotein lipase calibration system is an easy and very cheap arrangement, which makes it possible to compare lipoprotein lipase activities achieved over years. When the lipoprotein lipase control values are compared with reference lipoprotein lipase samples determined in other lipase laboratories, the calibration-control system becomes an important tool for reducing analytical bias. The article reviews the original analytical criteria of catalytic measurement of lipoprotein lipase activity and describes the implementation of the calibration-control system. We describe a model for reduction of the analytical variability in the measurement of lipoprotein lipase activity. Other standardization efforts need to be made in the future, especially to define the reference material for calibration.

Genetic dissection of familial combined hyperlipidemia

Familial combined hyperlipidemia (FCHL) is the most common genetic hyperlipidemia in man. FCHL is characterized by familial clustering of hyperlipidemia and clinical manifestations of premature coronary heart disease, i.e., before the age of 60. Although FCHL was delineated about 25 years ago, at present the FCHL phenotype and its complex genetics are not fully understood. Initially, the familial aggregation of high plasma total cholesterol and triglyceride levels, with a bimodal distribution of triglycerides, was taken as evidence of a dominant mode of inheritance. However, it is now clear that the genetics of FCHL is more complex, and it has been suggested that FCHL is heterogeneous. Several approaches can be taken to identify genes contributing to the disease phenotype in complex genetic disorders either by studying the disease in the human situation or by using animal models. Recent reports have shown that a combination of genetic linkage studies, association studies, and differential gene expression studies provides a useful tool for the genetic dissection of complex diseases. Therefore, the genetic strategies that will be used to dissect the genetic background of FCHL are reviewed.

Identification of a common variant in the lipoprotein lipase gene in a large Utah kindred ascertained for coronary heart disease: the -93G/D9N variant predisposes to low HDL-C/high triglycerides

Defects in the lipoprotein lipase (LPL) gene are associated with dyslipidemia in the general population. Several rare mutations in the gene, as well as two common coding region polymorphisms, D9N and N291S, exhibit deleterious effects on circulating lipid levels. Using a linkage-based approach, we have identified a large Utah kindred segregating the D9N variant in the LPL gene. The kindred was ascertained for premature coronary heart disease and was expanded based on familial dyslipidemia. A genomic scan identified a region of linkage including LPL, and mutation screening identified the segregating variant. In the kindred, the variant shows high penetrance for a hypoalphalipoproteinemia phenotype, but is also associated with hypertriglyceridemia and elevated insulin levels. The strength of linkage was dependent on the combination of phenotype definition and model parameters, favoring the use of a MOD score approach. Most other studies of LPL have proceeded by mutation screening of randomly chosen individuals or selected affected probands; this is the first example identifying a segregating LPL mutation using direct linkage.

Roles for lipoprotein lipase in Alzheimer's disease: an association study

Lipoprotein lipase (LPL) assists lipid transport by transferring lipids between lipoprotein particles and cells. LPL binds apolipoprotein E (apoE) lipoprotein particles and a major apoE receptor, low density lipoprotein receptor related protein (LRP). Because apoE and LRP polymorphisms alter Alzheimer's disease (AD) risk, and LPL itself is found in AD amyloid plaques, we examined whether LPL variants also affect AD risk. In case-control studies in the United States and Canada, the frequencies of two LPL alleles known to affect LPL enzymatic activity were measured in Caucasian AD or elderly normal (N) subjects. Pathologically confirmed subjects in both studies exhibited similar trends toward fewer 447Ter and more 291Ser alleles in AD. Combining results from both countries gave allele frequencies for 447Ter of 13.7% (26/190) in N and 9.4% (80/852) in AD (P = 0.10), and for 291Ser of 0.0% (0/184) in N and 1. 3% (8/636) in AD (P = 0.21). The trend appeared even greater for homozygous 447Ter subjects: 4.2% (4/95) of N vs. 1.4% (6/426) of AD (P = 0.09). These trends are consistent with a putative protective effect of 447Ter and causative effect of 291Ser on AD. Furthermore, brains of AD patients with 447Ter showed trends toward fewer plaques, tangles, and glia, and more neurons and cortical thickness than AD patients without 447Ter. Hippocampal plaques were significantly reduced. LPL might affect hippocampal function and thus dementia via its role as supplier of membrane components or antioxidants to neurons. Alternatively, LPL may play a part in plaque formation through its interaction with apoE and LRP.

Cardiovascular disease mortality in familial forms of hypertriglyceridemia: A 20-year prospective study

BACKGROUND

Familial combined hyperlipidemia (FCHL) and familial hypertriglyceridemia (FHTG) are 2 of the most common familial forms of hyperlipidemia. There is a paucity of prospective data concerning the risk of cardiovascular disease (CVD) in such families. The purposes of this study were to estimate 20-year total and CVD mortality risk among relatives in these families and to evaluate plasma triglyceride as a predictor of death.

METHODS AND RESULTS

The study was based on lipid and medical history data from 101 families ascertained in 2 studies conducted in the early 1970s. Vital status and cause of death was determined during 1993 to 1997 for 685 family members, including first-degree relatives of the probands and spouse control subjects. Compared with spouse control subjects, 20-year CVD mortality risk was increased among siblings and offspring in FCHL (relative risk 1.7, P=0.02) after adjustment for baseline covariates. In FHTG families, the relative risk was also 1.7 but was not statistically significant (P=0.39). Baseline triglyceride was associated with increased CVD mortality risk independent of total cholesterol among relatives in FHTG families (relative risk 2.7, P=0.02) but not in FCHL families (relative risk 1.5, P=0.16) after adjustment for baseline covariates.

CONCLUSIONS

This prospective study establishes that relatives in FCHL families are at increased risk for CVD mortality and illustrates the need for effective prevention strategies in this group. Baseline triglyceride level predicted subsequent CVD mortality among relatives in FHTG families, adding to the growing evidence for the importance of hypertriglyceridemia as a risk factor for CVD.

Lipoprotein lipase enhances the binding of native and oxidized low density lipoproteins to versican and biglycan synthesized by cultured arterial smooth muscle cells

Retention of low density lipoproteins (LDL) by vascular proteoglycans and their subsequent oxidation are important in atherogenesis. Lipoprotein lipase (LPL) can bind LDL and proteoglycans, although the effect of different proteoglycans to influence the ability of LPL to act as a bridge in the formation of LDL-proteoglycan complexes is unknown. Using an electrophoretic gel mobility shift assay, [(35)S]SO(4)-labeled versican and biglycan, two extracellular proteoglycans secreted by vascular cells, bound native LDL in a saturable fashion. The addition of bovine milk LPL dose-dependently increased the binding of native LDL to both versican and biglycan, approaching saturation at 30-40 microgram/ml LPL for versican and 20 microgram/ml LPL for biglycan. LDL was oxidized by several methods, including copper, 2, 2-azo-bis(2-amidinopropane)-2HCl and hypochlorite. Extensively copper- and hypochlorite-oxidized LDL bound poorly to versican and biglycan. Proteoglycan binding to LDL was correlated inversely with the extent of LDL; however, the addition of LPL to oxidized LDL together with biglycan or versican allowed the oxidized LDL to bind the proteoglycans in an LPL dose-dependent manner. Addition of LPL had a greater relative effect on the binding of extensively oxidized LDL to proteoglycans compared with native LDL. LPL had a slightly greater effect on increasing the binding of native and oxidized LDL to biglycan than versican. Thus, LPL in the artery wall might increase the atherogenicity of oxidized LDL, since it enables its binding to vascular biglycan and versican.

Linkage of a candidate gene locus to familial combined hyperlipidemia: lecithin:cholesterol acyltransferase on 16q

Familial combined hyperlipidemia (FCHL) is a common lipid disorder characterized by elevated levels of plasma cholesterol and triglycerides that is present in 10% to 20% of patients with premature coronary artery disease. To study the pathophysiological basis and genetics of FCHL, we previously reported recruitment of 18 large families. We now report linkage studies of 14 candidate genes selected for their potential involvement in the aspects of lipid and lipoprotein metabolism that are altered in FCHL. We used highly polymorphic markers linked to the candidate genes, and these markers were analyzed using several complementary, nonparametric statistical allele-sharing linkage methodologies. This current sample has been extended over the one in which we identified an association with the apolipoprotein (apo) AI-CIII-AIV gene cluster. We observed evidence for linkage of this region and FCHL (P<0.001), providing additional support for its involvement in FCHL. We also identified a new locus showing significant evidence of linkage to the disorder: the lecithin:cholesterol acyltransferase (LCAT) locus (P<0.0006) on chromosome 16. In addition, analysis of the manganese superoxide dismutase locus on chromosome 6 revealed a suggestive linkage result in this sample (P<0.006). Quantitative traits related to FCHL also provided some evidence of linkage to these regions. No evidence of linkage to the lipoprotein lipase gene, the microsomal triglyceride transfer protein gene, or several other genes involved in lipid metabolism was observed. The data suggest that the lecithin:cholesterol acyltransferase and apolipoprotein AI-CIII-AIV loci may act as modifying genes contributing to the expression of FCHL.

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.

Association of pre-eclampsia with common coding sequence variations in the lipoprotein lipase gene

Marked dyslipidemia may contribute to endothelial cell dysfunction in pre-eclampsia. Carriers of N291S or D9N missense mutations in the lipoprotein lipase (LPL) gene exhibit reductions in LPL activity and are predisposed to dyslipidemia and cardiovascular disease. In Caucasians, the D9N variant is in strong linkage disequilibrium with the - 93T --> G promoter variant. A fourth LPL variant, S447X, is often associated with a beneficial lipid profile. We asked if the N291S and the combination D9N/- 93T --> G variants are more prevalent, and if the S447X variant is less prevalent, in Caucasian women with pre-eclampsia as compared with normal pregnancies. DNA amplification was followed by an allele-specific oligonucleotide ligation assay. Allele frequencies were analyzed with a chi2 table and Yates' correction. The N291S variant was identified in 11.1% of pre-eclamptics as compared with 2.9% of pregnancy controls (p = 0.008). All carriers of D9N were also carriers of - 93T --> G. The D9N/ - 93T --> G combined variant was found in 7.1% of pre-eclamptics as compared with 1.4% of pregnancy controls (p = 0.02). No individuals were carriers of both N291S and D9N/ - 93T --> G. Thus, 18.2% of pre-eclamptics had either of these LPL mutations compared with 4.3% of pregnancy controls (and 4.4% of population controls). The frequency of the S447X variant did not differ among groups. We conclude that carriers of N291S or combined D9N/ - 93T --> G mutations in the LPL gene are at substantially increased risk of pre-eclampsia.

Pleiotropic genetic effects on LDL size, plasma triglyceride, and HDL cholesterol in families

The interrelationships among low density lipoprotein (LDL) particle size, plasma triglyceride (TG), and high density lipoprotein cholesterol (HDL-C) are well established and may involve underlying genetic influences. This study evaluated common genetic effects on LDL size, TG, and HDL-C by using data from 85 kindreds participating in the Genetic Epidemiology of Hypertriglyceridemia (GET) Study. A multivariate, maximum likelihood-based approach to quantitative genetic analysis was used to estimate the additive effects of shared genes and shared, unmeasured nongenetic factors on variation in LDL size and in plasma levels of TG and HDL-C. A significant (P<0.001) proportion of the variance in each trait was attributable to the additive effects of genes. Maximum-likelihood estimates of heritability were 0.34 for LDL size, 0.41 for TG, and 0.54 for HDL-C. Significant (P<0.001) additive genetic correlations (rho(G)), indicative of the shared additive effects of genes on pairs of traits, were estimated between all 3 trait pairs: for LDL size and TG rho(G)=-0.87, for LDL size and HDL-C rho(G)=0.65, and for HDL-C and TG rho(G)=-0.54. A similar pattern of significant environmental correlations between the 3 trait pairs was also observed. These results suggest that a large proportion of the well-documented correlations in LDL size, TG, and HDL-C are likely attributable to the influence of the same gene(s) in these families. That is, the gene(s) that may contribute to decreases in LDL size also contribute significantly to higher plasma levels of TG and lower plasma levels of HDL-C. These relationships may be useful in identifying genes responsible for the associations between these phenotypes and susceptibility to cardiovascular disease in these families.

Functional variants in the lipoprotein lipase gene and risk cardiovascular disease

The current report is a quantitative review of the relationship between lipoprotein lipase gene variants and cardiovascular disease based on published population-based studies. Sixteen studies, representing 17,630 individuals, report allelic distribution for lipoprotein lipase gene variants among patients and control individuals. Patient outcomes included clinical cardiovascular disease events, documented coronary disease based on angiography, or intimal media thickening by B-mode ultrasonography. Mantel-Haenszel stratified analysis was used to compute a summary odds ratio and 95% confidence intervals for the association between rare allele in the lipoprotein lipase gene and disease status. Because of potential differing effects associated with different lipoprotein lipase variants, each lipoprotein lipase mutant allele was considered separately. The lipoprotein lipase D9N/-93G to T allele has a summary odds ratio of 2.03 (95% confidence interval 1.30-3.18), indicating a twofold increase in risk of coronary disease for carriers with this allelic variant. The summary odds ratio for the relationship of the rare lipoprotein lipase G188E variant with cardiovascular disease is 5.25 (95% confidence interval 1.54-24.29). The lipoprotein lipase N291S allele is associated with a marginal increase in cardiovascular disease (summary odds ratio 1.25, 95% confidence interval 0.99-1.60, P = 0.07). However, there is stronger evidence for a positive association in certain populations. The summary odds ratio for lipoprotein lipase S447X allele is 0.81 (95% confidence interval 0.65-1.0), which indicates a cardioprotective effect of this lipoprotein lipase gene variant. Thus, lipoprotein lipase gene variants are associated with differential susceptibility to cardiovascular disease.

Common mutations of the lipoprotein lipase gene and their clinical significance

The accumulation of triglyceride-rich lipoproteins is an independent factor for an increased risk for premature arteriosclerosis. Common mutations in the lipoprotein lipase (LPL) gene are at least in part inherited susceptibility factors involved in the age- and sex-dependent phenotypic expression of hypertriglyceridemia. It can be estimated that about 20% of patients with hypertriglyceridemia are carriers of common LPL gene mutations (Asp9Asn, Asn291Ser, Trp86Arg, Gly188Glu, Pro207Leu, Asp250Asn) associated with the HLP. Genotyping of these LPL gene mutations is recommended especially in patients with high risk for premature arteriosclerosis. A comparably high number of individuals are carriers of common mutations (Ser447X) or silent mutations (Thr361) associated with low favorable lipids.

Genetics of familial combined hyperlipidemia

Complex disorders are caused by several environmental factors that interact with multiple genes. These diseases are common at the population level and constitute a major health problem in Western societies. Familial combined hyperlipidemia (FCHL) is characterized by elevated levels of serum total cholesterol, triglycerides, or both. This disorder is estimated to be common in Western populations with a prevalence of 1% to 2%. In addition, 14% of patients with premature coronary heart disease (CHD) have FCHL, making this disorder one of the most common genetic dyslipidemias underlying premature CHD. Both genetic and environmental factors are suggested to affect the complex FCHL phenotype, but no specific susceptibility genes to FCHL have been identified. It is hoped that further analysis of the first FCHL locus and other new loci obtained in genome-wide scans will guide us to genes predisposing to this complex disorder.

Lipoprotein lipase mutations, plasma lipids and lipoproteins, and risk of ischemic heart disease. A meta-analysis

BACKGROUND

We assessed in meta-analyses the effect of the Gly188Glu, Asp9Asn, Asn291Ser, and Ser447Ter substitutions in lipoprotein lipase in the heterozygous state on lipid metabolism and risk of ischemic heart disease (same order used below).

METHODS AND RESULTS

In 29 separate studies, 20 903 white subjects were screened for >/=1 of these substitutions; each meta-analysis included only some of these individuals. In population-based studies, heterozygote frequencies ranged from 0.04% to 0.2%, 2% to 4%, 1% to 7%, and 17% to 22% for the respective substitutions. Postheparin plasma lipoprotein lipase activity decreased 53% (95% CI, 31% to 75%) (only 1 study), 30% (22% to 37%), and 22% (8% to 35%) and was unchanged at 4% (-10% to 19%), respectively. Plasma triglycerides increased 78% (95% CI, 64% to 92%), 20% (9% to 33%), and 31% (20% to 43%) and decreased 8% (4% to 11%), respectively. HDL cholesterol decreased 0. 25 mmol/L (0.18 to 0.32), 0.08 mmol/L (0.04 to 0.12), and 0.12 mmol/L (0.10 to 0.15) and increased 0.04 mmol/L (0.02 to 0.06), respectively. Odds ratios for ischemic heart disease were 4.9 (95% CI, 1.2 to 20) (only 1 study), 1.4 (0.8 to 2.4), 1.2 (0.9 to 1.5), and 0.8 (0.7 to 1.0), respectively. Subgroup analysis indicated that women with the Asn291Ser substitution may have an increased risk of ischemic heart disease.

CONCLUSIONS

These meta-analyses suggest that compared with noncarriers, carriers of the Gly188Glu, Asp9Asn, and Asn291Ser substitutions have an atherogenic lipoprotein profile, whereas carriers of the Ser447Ter substitution have a protective lipoprotein profile. Accordingly, risk of ischemic heart disease in heterozygous carriers is increased for Gly188Glu carriers; at most, the increase is borderline for Asp9Asn and Asn291Ser carriers; and risk is possibly decreased for Ser447Ter carriers.

Mutations in the lipoprotein lipase gene associated with ischemic heart disease in men. The Copenhagen city heart study

The aim of this study was to test the hypothesis that the Asp9Asn substitution and the T(-93)-->G mutation in the promoter of the lipoprotein lipase gene affect plasma lipid levels and thereby the risk of ischemic heart disease (IHD). We genotyped 9033 men and women from a general population sample and 940 patients with IHD. The frequency of both the G allele and the Asn9 allele in the general population sample was approximately 0.015 for both men and women. These 2 mutations appeared together in 95% of carriers. The average triglyceride-raising effect associated with double heterozygosity for the T(-93)-->G mutation and the Asp9Asn substitution was 0.28 mmol/L (P=0.004) and 0.16 mmol/L (P=0.10) in men and women, respectively. On logistic regression analysis allowing for age, the risk of IHD for double heterozygous men and women was increased 90% (95% confidence interval [CI], 20% to 200%) and 30% (95% CI, -40% to 170%), respectively, compared with noncarriers. When, in addition, other conventional cardiovascular risk factors were allowed for, the risk of IHD for double heterozygous men and women was increased 70% (95% CI, 0% to 190%) and 20% (95% CI, -50% to 180%), respectively. Of the overall risk of IHD in men in the general population, the fraction attributable to double heterozygosity was 3%, similar to the 5% attributable to diabetes mellitus. These results demonstrate that the Asp9Asn substitution is in linkage disequilibrium with the T(-93)-->G mutation and that the double-heterozygous carrier status is associated with elevated plasma triglycerides and an increased risk of IHD in men.

Lipoprotein lipase mutations and Alzheimer's disease

Lipoprotein lipase (LPL) helps transfer lipids from lipoprotein particles to cells. In the brain, LPL is present in Alzheimer's disease (AD) amyloid plaques. LPL binds apolipoprotein E (ApoE) lipoprotein particles and low-density lipoprotein receptor-related protein (LRP), an ApoE receptor. Since polymorphisms in both ApoE and LRP influence AD risk, we sought to determine whether LPL mutations also affect AD risk. In a case-control study, the frequencies of two of the most common known LPL mutations were measured in European-Americans either clinically diagnosed or pathologically confirmed as AD or normal control (N) subjects. In clinically diagnosed subjects, the Ser447Ter mutation comprised 9.8% (62/630) of alleles in N and 3.8% (9/238) in AD, a significant difference (P = 0.0057), while the Asn291Ser mutation comprised 1.1% (5/460) of alleles in N and 5.1% (8/158) in AD, also a significant difference (P = 0.0073), though in pathologically confirmed subjects the allele frequencies for AD did not significantly differ from N for either mutation. In clinically diagnosed subjects, LPL mutations were associated with altered AD risk, suggesting a potential role for LPL in the causation of AD. Further studies in different populations should help clarify the questions raised by these results.

The genetics of serum lipid responsiveness to dietary interventions

CHD is a multifactorial disease that is associated with non-modifiable risk factors, such as age, gender and genetic background, and with modifiable risk factors, including elevated total cholesterol and LDL-cholesterol levels. Lifestyle modification should be the primary treatment for lowering cholesterol values. The modifications recommended include dietary changes, regular aerobic exercise, and normalization of body weight. The recommended dietary changes include restriction in the amount of total fat, saturated fat and cholesterol together with an increase in the consumption of complex carbohydrate and dietary fibre, especially water-soluble fibre. However, nutrition scientists continue to question the value of these universal concepts and the public health benefits of low-fat diets, and an intense debate has been conducted in the literature on whether to focus on reduction of total fat or to aim efforts primarily towards reducing the consumption of saturated and trans fats. Moreover, it is well known that there is a striking variability between subjects in the response of serum cholesterol to diet. Multiple studies have examined the gene-diet interactions in the response of plasma lipid concentrations to changes in dietary fat and/or cholesterol. These studies have focused on candidate genes known to play key roles in lipoprotein metabolism. Among the gene loci examined, APOE has been the most studied, and the current evidence suggests that this locus might be responsible for some of the inter-individual variability in dietary response. Other loci, including APOA4, APOA1, APOB, APOC3, LPL and CETP have also been found to account for some of the variability in the fasting and fed states.

Relative contribution of low-density lipoprotein receptor and lipoprotein lipase gene mutations to angiographically assessed coronary artery disease among French Canadians

Men with low-density lipoprotein receptor gene mutations causing familial hypercholesterolemia (FH) are at high risk of premature coronary artery disease (CAD). The dyslipidemic state found among patients who are heterozygous for mutations in the lipoprotein lipase (LPL) gene may also increase the risk of CAD. In the present study, the association of the heterozygous forms of low-density lipoprotein receptor gene mutations causing FH as well as of LPL gene mutations causing (P207L and G188E) or not causing (D9N and N291S) complete loss of LPL activity with angiographically assessed CAD was estimated in a cohort of 412 French Canadian men aged <60 years who consecutively underwent coronary angiography for the investigation of retrosternal pain. The frequency of FH as well as of LPL gene mutations tended to increase with the number of narrowed coronary arteries. However, CAD occurred earlier in FH patients than in partly LPL-deficient patients. Indeed, the proportion of men affected by FH was of 16.4% in those <45 years of age, and solely 4.3% among those between 56 and 60 years of age (p <0.0001). In contrast, the LPL gene defect was found in only 4.0% of men aged <45 years, whereas this prevalence reached 8.3% among those aged 56 to 60 years. In multivariate analyses, the association of LPL with CAD was not independent of age, high-density lipoprotein cholesterol concentrations, and other covariates included at baseline, and was not affected by the type of mutation in the LPL gene. In contrast, FH was associated with CAD with minimal contribution of other cardiovascular risk factors. However, the relation between FH and CAD was at least partly dependent on plasma apolipoprotein B concentrations. In the different regression models, fasting insulin and plasma high-density lipoprotein cholesterol concentrations were important covariates of CAD, whether or not patients were affected by FH or LPL deficiency. In conclusion, the association of LPL gene mutations with CAD was delayed compared with FH, appeared to be markedly exacerbated by the presence of additional risk factors, and was not affected by the type of mutation in the LPL gene.

Defects of lipoprotein metabolism in familial combined hyperlipidaemia

Familial combined hyperlipidaemia is the most common inherited hyperlipidaemia and is found in up to 10% of patients with premature myocardial infarction. The genetic and metabolic bases of the disorder have not yet been defined. This review discusses the important advances in the past year in our understanding of the different metabolic pathways contributing to the pathogenesis of familial combined hyperlipidaemia.

Gender-related association between the -93T-->G/D9N haplotype of the lipoprotein lipase gene and elevated lipid levels in familial combined hyperlipidemia

Familial combined hyperlipidemia (FCHL) is a frequent cause of premature coronary artery disease. Affected family members are characterized by different combinations of elevated cholesterol and/or triglyceride levels. A reduction in lipoprotein lipase (LPL) activity has been observed in a subgroup of FCHL patients. Recently, we have demonstrated an increased frequency of mutations in the LPL gene in Dutch FCHL patients compared to normolipidemic controls. In the present study, we have applied a pedigree-based maximum likelihood method to study the effect of LPL mutations on the phenotypic expression of FCHL in families. In 40 FCHL probandi, three different previously reported mutations in the LPL gene were identified resulting in amino acid changes, D9N, N291S, and S447X. The D9N mutation in exon 2 appeared to be in strong linkage disequilibrium with a T-->G substitution at position -93 in the promoter region of the LPL gene. We present data that the -93T-->G/D9N haplotype is associated with significantly higher levels of LDL and VLDL cholesterol, and VLDL triglycerides. Interestingly, the effect was only observed in male carriers. In line with our previous observations, these results further sustain that the LPL gene is a susceptibility gene for dyslipidemia which explains part of the variability in the phenotype observed among FCHL family members.

Common variation in the lipoprotein lipase gene: effects on plasma lipids and risk of atherosclerosis

The importance of the enzyme lipoprotein lipase (LPL) in the development of dyslipidaemia and atherosclerosis is increasingly recognised. Variations in the LPL gene which are common in the general population have been shown to be associated with alterations in plasma lipids. D9N and N291S both occur at carrier frequencies of up to about 5% and have been associated with increased plasma triacylglycerol and decreased high density lipoprotein cholesterol concentrations, effects which seem to be magnified in more obese individuals. S447X carrier frequency is approximately 20%, but unlike carriers of N9 or S291, X447 carriers appear to have a more favourable lipid profile. A transition within the LPL promoter at position-93 may lead to increased LPL activity and have a beneficial effect on plasma lipids. Greater knowledge of the underlying mechanisms of these variations within the LPL gene may be of considerable importance in understanding genetic predisposition to atherosclerosis and heart disease.