Genetic variants in adipose triglyceride lipase influence lipid levels in familial combined hyperlipidemia.

OBJECTIVE: Familial combined hyperlipidemia (FCHL) has been associated with abnormalities in fatty acid metabolism. The adipose triglyceride lipase (PNPLA2) plays a pivotal role in the turnover of fatty acids in adipose tissue and liver. This study was designed to evaluate whether selected PNPLA2 variants may influence the susceptibility to FCHL or its lipid-related traits. METHODS: Four SNPs within the PNPLA2 gene (rs7925131, rs7942159, rs66460720 and the nonsynonymous P481L) were selected based on previous association with decreased plasma levels of free fatty acids (FFA) and total triglycerides (TG) and their high frequency (MAF>0.25). These SNPs were genotyped in 214 FCHL individuals from 83 families and in 103 controls and the corresponding haplotypes were reconstructed. RESULTS: No association between individual SNPs and the FCHL trait was observed. However, two PNPLA2 haplotypes were associated with lower risk of FCHL (P<0.004 after Bonferroni's correction). Compared to the others, these haplotypes were related to lower TG (118.9 ± 66.8 vs. 197.1 ± 114.7 mg/dl; P=0.001) and higher HDL-C (62.3 ± 15.8 vs. 51.0 ± 15.0 mg/dl; P<0.005). In a subgroup of studied subjects (n=63) protective haplotypes were also associated with lower FFA levels (0.33 ± 0.11 vs. 0.46 ± 0.18 mEq/L; P<0.05). These effects were independent from age, BMI and HOMA(IR). CONCLUSION: These data demonstrate that variants within PNPLA2 may modulate the TG component of FCHL trait, thus implicating PNPLA2 as modifier gene in this lipid disorder. They also suggest a potential role of PNPLA2 in the metabolism of TG-rich lipoproteins.

Prevalence and clinical features of heterozygous carriers of autosomal recessive hypercholesterolemia in Sardinia.

OBJECTIVE: Autosomal recessive hypercholesterolemia (ARH) is a lipid disorder caused by mutations in a specific adaptor protein for the LDL receptor. ARH is rare except in Sardinia where three alleles (ARH1, ARH2 and ARH3) explain most of cases. The prevalence of ARH heterozygotes in Sardinia is not well determined as well as inconclusive data are available on the effect of the ARH carrier status on LDL cholesterol (LDL-C) and coronary risk. METHODS: 3410 Sardinians (986 blood donors, 1709 with hypertension and 715 with myocardial infarction (MI)) were screened for ARH alleles. For comparison purposes, lipid data of 60 ARH heterozygous carriers and 60 non-carriers identified within 24 ARH families were also considered. RESULTS: In the whole study cohort, no ARH homozygotes were found, but 15 ARH1 (0.44%) and 9 ARH2 (0.26%) heterozygous carriers were identified. The frequency of ARH alleles in blood donors was 0.0030, not different from that in hypertensive subjects (0.0032). ARH alleles tended to be more common in MI patients (0.0049), but no association between ARH carrier status and MI risk was detected after controlling for conventional risk factors. ARH carriers and non-carriers showed similar LDL-C levels. This result was confirmed when ARH carriers and non-carriers identified throughout family-based and population-based screenings were combined and compared (141.0+/-41 mg/dl vs. 137.0+/-41 mg/dl, respectively; p=0.19). CONCLUSIONS: These data indicate that the frequency of ARH heterozygotes in Sardinia is approximately 1:143 individuals, thus making this condition one of the most common in the Sardinian population. However, ARH carrier status does not influence LDL-C concentration and coronary risk, thus suggesting that ARH can be regarded as a truly recessive disorder.

Novel mutations in the adipose triglyceride lipase gene causing neutral lipid storage disease with myopathy.

A subgroup of neutral lipid storage disease has been recently associated with myopathy (NLSDM) and attributed to mutations in the gene (PNPLA2) encoding an adipose triglyceride lipase involved in the degradation of intracellular triglycerides. Five NLSDM patients have been described thus far and we reported three additional patients. A 44-year old Iranian woman and two Italian brothers, aged 40 and 35, presented with exercise intolerance and proximal limb weakness, elevated CK levels, and Jordan's anomaly. Muscle biopsies showed marked neutral lipid accumulation in all patients. The 10 exons and the intron-exon junctions of the PNPLA2 gene were sequenced. Two novel homozygous mutations in exon 5 of PNPLA2 gene were found (c.695delT and c.542delAC). Both mutations resulted in frameshifts leading to premature stop codons (p.L255X and p.I212X, respectively). These mutations predict a truncated PNPLA2 protein lacking the C-terminal hydrophobic domain. These findings indicate that NLSDM is rare, but genetically heterogeneous.

C242T polymorphism of NADPH oxidase p22phox and recurrence of cardiovascular events in coronary artery disease.

OBJECTIVE: The common C242T polymorphism in the gene for the p22phox subunit of NADPH oxidase has been reported to be negatively associated with oxidative stress, but whether it confers prognostic information is not yet clear. METHODS AND RESULTS: The incidence of major adverse cardiovascular events (MACE) were determined in 237 patients with coronary stenosis during a median follow-up of 7.8 years. The p22phox genotypes were evaluated in 213 patients (89.9%) by polymerase chain reaction and RsaI. digestion. Plasma levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG), a marker of oxidative stress, were also measured. In the univariate analysis, patients with CT/TT genotypes showed reduced recurrence of cardiovascular deaths, nonfatal MI, and revascularization procedures compared with homozygous carriers of the C allele. After controlling for confounders, a significantly lower risk of new revascularization procedures (HR=0.31, 95% CI 0.12 to 0.70; P=0.014) remained associated with the T allele. The Kaplan-Meier analysis showed a longer survival free from fatal and nonfatal MI in carriers of T allele (P<0.001). The presence of the 242T allele was associated with significantly reduced plasma concentrations of 8-OHdG. CONCLUSIONS: The 242T allele was a predictor of lower risk of recurrence of cardiovascular events in high-risk patients and was associated with reduced systemic oxidative stress.

Detection of familial hypercholesterolemia in a cohort of children with hypercholesterolemia: results of a family and DNA-based screening.

The diagnosis of familial hypercholesterolemia (FH) in unselected children is difficult due to the frequent overlap of cholesterol values in affected and non-affected and the paucity of physical signs. Nevertheless, detection and treatment of FH in childhood has been advocated to prevent atherosclerosis in these patients. Here, we report the results of a screening program in a cohort of 157 unrelated, hypercholesterolemic (HC) children (age range 2-15 years; mean 8.3+/-3.4 years) carried out by a combination of family study and molecular analysis of the LDLR gene. On the basis of the familial phenotype, 27 (17.2%) were classified as probable FH and 49 (31.2%) as affected by FCHL. Among probable FH children, 14 (51.8%) carried mutant LDLR alleles, giving an overall 8.9% prevalence of FH. Most of LDLR variants were already reported, but three new mutations G266C, T368M, and D451Y were identified. Beside increased TC and LDL-C (p<0.001), FH children showed decreased HDL-C (p<0.05) and higher prevalence of family history of CAD when compared to non-FH children. None presented tendon xanthomas. We estimated that LDL-C >3.9 mmol/L was the best cut off value for diagnosing FH in these children, showing 79% sensitivity and 71.0% specificity. We propose the use of a LDL-C cut off level associated with a family study to identify FH among HC children.

Usefulness of atherogenic dyslipidemia for predicting cardiovascular risk in patients with angiographically defined coronary artery disease.

The identification of factors contributing to residual cardiovascular risk is important to improve the management of patients with established coronary artery disease (CAD). This study was conducted to assess the predictive value of atherogenic dyslipidemia (defined as high triglycerides and low high-density lipoprotein [HDL] cholesterol) for long-term outcomes in patients with CAD. In 284 patients (238 men, 46 women; mean age at baseline 59.2 +/- 8.9 years) with coronary stenosis (>50% in > or =1 vessel), the presence of atherogenic dyslipidemia was prospectively associated with the incidence of major adverse cardiovascular events (MACEs) during a median follow-up of 7.8 years. MACEs were defined as cardiovascular death, nonfatal myocardial infarction, nonfatal stroke, the recurrence of angina, and revascularization procedures. MACEs were observed in 111 (39.1%) patients with CAD. MACEs occurred more frequently in patients with atherogenic dyslipidemia (50.9%) than in those with isolated low HDL cholesterol or high triglycerides (33.0%) or with normal HDL cholesterol and triglyceride concentrations (29.2%) (p <0.01 for trend). Kaplan-Meier survival analysis showed a decrease in event-free survival in patients with compared with those without atherogenic dyslipidemia (log-rank p = 0.006). Patients with atherogenic dyslipidemia presented with increased plasma concentrations of remnants, denser low-density lipoprotein, more atherogenic HDL particles, and insulin-resistant status. After adjustment for potential confounding variables, the magnitude of increased risk associated with atherogenic dyslipidemia was 1.58 (95% confidence interval 1.12 to 2.21, p = 0.008). In conclusion, these data provide evidence that atherogenic dyslipidemia is an independent predictor of cardiovascular risk in patients with CAD, even stronger than isolated high triglycerides or low HDL cholesterol.

Autosomal recessive hypercholesterolemia in Spanish kindred due to a large deletion in the ARH gene.

Autosomal recessive hypercholesterolemia (ARH) is a rare genetic defect that causes marked elevation of plasma low-density lipoprotein cholesterol (LDL-C) and premature atherosclerosis. It is due to mutations in the ARH gene that plays a critical role in the internalization of LDL receptor (LDLR) in liver cells. We describe a Spanish family where a 24-year-old proband and his 13-year-old sister showed the typical characteristics of ARH. The proband's LDLR activity in peripheral lymphocytes was 14% of normal and his in vivo LDL catabolism was reduced by 64% compared to normal. Notably, the sister showed normal lipid levels when her umbilical cord blood was tested. In this family, ARH was due to homozygosity for a large approximately 1.6kb deletion that eliminates exon 4 of ARH gene. Analysis of ARH mRNA demonstrated that the fusion of exon 3 to exon 5 during the splicing of the primary transcript changes the reading frame leading to stop codon 7 amino acids downstream in exon 5. No protein product was detected in affected individuals by immunoblot analysis. This novel mutation adds new support to the molecular heterogeneity of ARH in the Mediterranean basin.

Adaptor protein ARH is recruited to the plasma membrane by low density lipoprotein (LDL) binding and modulates endocytosis of the LDL/LDL receptor complex in hepatocytes.

ARH is a newly discovered adaptor protein required for the efficient activity of low density lipoprotein receptor (LDLR) in selected tissues. Individuals lacking ARH have severe hypercholesterolemia due to an impaired hepatic clearance of LDL. It has been demonstrated that ARH is required for the efficient internalization of the LDL-LDLR complex and to stabilize the association of the receptor with LDL in Epstein-Barr virus-immortalized B lymphocytes. However, little information is available on the role of ARH in liver cells. Here we provide evidence that ARH is codistributed with LDLR on the basolateral area in confluent HepG2-polarized cells. This distribution is not modified by the overexpression of LDLR. Conversely, the activation of the LDLR-mediated endocytosis, but not the binding of LDL to LDLR, promotes a significant colocalization of ARH with LDL-LDLR complex that peaked at 2 min at 37 degrees C. To further assess the role of ARH in LDL-LDLR complex internalization, we depleted ARH protein using the RNA interference technique. Twenty-four hours after transfection with ARH-specific RNA interference, ARH protein was depleted in HepG2 cells by more than 70%. Quantitative immunofluorescence analysis revealed that the depletion of ARH caused about 80% reduction in LDL internalization. Moreover, our findings indicate that ARH is associated with other proteins of the endocytic machinery. We suggest that ARH is an endocytic sorting adaptor that actively participates in the internalization of the LDL-LDLR complex, possibly enhancing the efficiency of its packaging into the endocytic vesicles.

A polymorphism in the cyclooxygenase 2 gene as an inherited protective factor against myocardial infarction and stroke.

CONTEXT: Myocardial infarction (MI) and ischemic stroke are thought to be caused by matrix digestion by metalloproteinases (MMPs) leading to rupture of atherosclerotic plaques. Production of macrophage MMP-2 and MMP-9 is induced by cyclooxygenase 2 (COX-2) and prostaglandin E(2) synthesis. Although COX-2 expression may be genetically determined, the relation between COX-2 polymorphisms and the risk of MI and stroke is unclear. OBJECTIVE: To investigate the relationship between the -765G-->C polymorphism of the COX-2 gene and clinically evident plaque rupture. DESIGN, SETTING, AND PARTICIPANTS: Prospective, matched case-control study conducted between March 2002 and October 2003 among 864 patients with first MI or atherothrombotic ischemic stroke and 864 hospitalized controls. The groups were matched for age, sex, body mass index, smoking, hypertension, hypercholesterolemia, and diabetes. The -765G-->C variant of the COX-2 gene was genotyped by restriction endonuclease digestion of polymerase chain reaction products. MAIN OUTCOME MEASURES: Presence of the -765G-->C polymorphism of the COX-2 gene; COX-2, MMP-2, and MMP-9 expression and activity in plaques and in peripheral monocytes; urinary 6-keto PGF1alpha (marker of endothelial prostacyclin); and endothelium-dependent and -independent forearm blood flow vasodilation. RESULTS: The prevalence of -765GC was 2.41 times higher among controls than among cases (43.3% vs 17.9%; P<.001). The prevalence of -765CC homozygosity was 5.81 times higher (6.4% vs 1.1%; P =.04). Among participants carrying the -765GC and -765CC genotypes, the prevalence ratios for MI or stroke were 0.48 (95% CI, 0.36-0.68) and 0.33 (95% CI, 0.24-0.55), respectively. Expression of COX-2 and MMPs was significantly lower in atherosclerotic plaques from participants carrying the -765C allele, while the -765G-->C polymorphism did not affect endothelial prostacyclin biosynthesis or endothelium-dependent vasodilation in vivo. In subgroup analyses (n = 224 cases), serum high-sensitivity C-reactive protein was significantly lower in patients carrying the -765C allele (mean [SD], 0.78 [0.1] vs 2.56 [0.4] mg/L; P =.04). CONCLUSIONS: We found that the -765G-->C polymorphism of the COX-2 gene is associated with a decreased risk of MI and stroke. Detection of this genotype may be useful for predicting genetic risk of MI and stroke.

Molecular mechanisms of autosomal recessive hypercholesterolemia.

Mutations in the phosphotyrosine-binding domain protein ARH cause autosomal recessive hypercholesterolemia (ARH), an inherited form of hypercholesterolemia due to a tissue-specific defect in the removal of low density lipoproteins (LDL) from the circulation. LDL uptake by the LDL receptor (LDLR) is markedly reduced in the liver but is normal or only moderately impaired in cultured fibroblasts of ARH patients. To define the molecular mechanism underlying ARH we examined ARH mRNA and protein in fibroblasts and lymphocytes from six probands with different ARH mutations. None of the probands had detectable full-length ARH protein in fibroblasts or lymphoblasts. Five probands were homozygous for mutations that introduced premature termination codons. No relationship was apparent between the site of the mutation in ARH and the amount of mRNA. The only mutation identified in the remaining proband was a SINE VNTR Alu (SVA) retroposon insertion in intron 1, which was associated with no detectable ARH mRNA. (125)I-LDL degradation was normal in ARH fibroblasts, as previously reported. In contrast, LDLR function was markedly reduced in ARH lymphoblasts, despite a 2-fold increase in LDL cell surface binding in these cells. These data indicate that all ARH mutations characterized to date preclude the synthesis of full-length ARH and that ARH is required for normal LDLR function in lymphocytes and hepatocytes, but not in fibroblasts. Residual LDLR function in cells that do not require ARH may explain why ARH patients have lower plasma LDL levels than do patients with homozygous familial hypercholesterolemia who have no functional LDLRs.

Common variants in the lipoprotein lipase gene, but not those in the insulin receptor substrate-1, the beta3-adrenergic receptor, and the intestinal fatty acid binding protein-2 genes, influence the lipid phenotypic expression in familial combined hyperlipidemia.

Familial combined hyperlipidemia (FCHL) is a common, atherogenic lipid disorder characterized by a variable phenotypic expression of hyperlipidemia. Variations in genes regulating fatty acid metabolism must be considered in the search for factors affecting the lipid phenotypic expression of FCHL. Therefore, we have evaluated the association of the common variants in the lipoprotein lipase (LPL) (D9N, N291S, and S447X), insulin receptor substrate-1 (IRS-1) (G972R), fatty acid binding protein-2 (FABP-2) (A54T), and beta3-adrenergic receptor (beta3-AR) (W64R) genes with lipid and lipoprotein levels in 30 Italian FCHL families (195 individuals). The transmission disequilibriun test (TDT) was used to evaluate the association between these variants and the FCHL trait. No significant differences were observed in the frequencies of the common LPL variants between affected and nonaffected FCHL family members. A significantly lower frequency of the LPL447X allele was noted only when members of the FCHL families were compared with normolipemic controls (.06 v.142, respectively; P <.01) suggesting a reduced representation of this LPL variant in FCHL families. The frequencies of variants in the IRS-1, FABP-2, and beta3-AR genes were not significantly different between affected and nonaffected FCHL family members and normolipemic controls. The TDT did not demonstrate any significant association of these gene variants with the FCHL trait. FCHL individuals carrying the LPL N291S gene showed higher plasma lipids and apolipoprotein B (apoB) levels compared with affected noncarriers. Only a marginal effect of the LPL D9N and S447X variants on lipid levels in FCHL individuals was observed. Conversely, the variants in the IRS-1, FABP2, and beta3-AR genes did not show any major influence on lipid and lipoprotein levels in FCHL family members. In conclusion, these results confirmed that none of the investigated genes were major loci for FCHL. Nevertheless, variations in genes affecting the removal rate of triglycerides (TG) from plasma, such as the LPL gene, significantly influence the lipid phenotypic expression of FCHL. Conversely, genetic variants in the IRS-1, FABP-2, and the beta3-AR gene appear not to have a major role as modifier genes in FCHL.

Autosomal recessive hypercholesterolaemia in Sardinia, Italy, and mutations in ARH: a clinical and molecular genetic analysis.

BACKGROUND: Autosomal recessive hypercholesterolaemia (ARH) is caused by mutations in a putative adaptor protein called ARH. This recessive disorder, characterised by severe hypercholesterolaemia, xanthomatosis, and premature coronary artery disease, is rare except on the island of Sardinia, Italy. Our aim was to ascertain why ARH is more common on Sardinia than elsewhere. METHODS: We obtained detailed medical histories, did physical examinations, measured concentrations of lipoproteins, and harvested genomic DNA from 28 Sardinians with ARH from 17 unrelated families. We sequenced the coding regions and consensus splice sites of ARH in probands from these families, and from 40 individuals of non-Sardinian origin who had an autosomal recessive form of hypercholesterolaemia of unknown cause. FINDINGS: Two ARH mutations, a frameshift mutation (c432insA) in exon 4 (ARH1) and a nonsense mutation (c65G-->A) in exon 1 (ARH2), were present in all of the 17 unrelated families with ARH. Three of the ARH alleles contained both mutations, as a result of an ancient recombination between ARH1 and ARH2. No regional clustering of the three mutant alleles within Sardinia was apparent. Furthermore, four Italians from the mainland with autosomal recessive hypercholesterolaemia were homozygous for ARH1. INTERPRETATION: The small number, high frequency, and dispersed distribution of ARH mutations on Sardinia are consistent with these mutations being ancient and maintained in the Sardinian population because of geographic isolation.