A presumptive new locus for autosomal dominant hypercholesterolemia mapping to 8q24.22.

Molecular testing of patients with autosomal dominant hypercholesterolemia (ADH) fails to detect a causal functional mutation in 15.25% of subjects. We studied an ADH pedigree in which known ADH-causing genes (LDLR, APOB and PCSK9) were excluded. Genome-wide analysis on 15 family members detected significant association for ADH and dbSNP RS ID rs965814 (G/A), located in 8q24.22 cytoband. ADH was significantly associated to rs965814 G allele (p < 0.05) in a case-control study based on 200 unrelated ADH subjects without LDLR or APOB gene defects and 198 normolipidemic controls. We chose 24 markers for a detailed analysis of 8q24.22 cytoband, now based on an extended set of family members (21 individuals). One particular 24 marker haplotype was significantly associated to both higher total and low-density lipoprotein-cholesterol concentrations. Similar results were found for a shorter haplotype, composed of the distal six markers from the complete haplotype. Therefore, a presumptive new locus for ADH could be located in 8q24.22 cytoband, a region not previously linked or associated to ADH.

Apolipoprotein E genotype is not associated with cardiovascular disease in heterozygous subjects with familial hypercholesterolemia.

BACKGROUND: Familial hypercholesterolemia (FH) is a genetic disorder characterized by high low-density lipoprotein cholesterol levels and premature cardiovascular disease (CVD). There are important differences in the presence of CVD among heterozygous subjects with FH. Some of this variability can be explained by genetic factors, and the apolipoprotein (apo) E genotype has been proposed as a useful marker. METHODS: We analyzed the apo E genotype in 706 non-related subjects who were heterozygous for FH from Spain. CVD was present in 198 subjects (28%), 132 men (41%) and 66 women (17%). RESULTS: Apo E allele frequencies for the epsilon 3, epsilon 4, and epsilon 2 alleles were 0.89, 0.09, and 0.02 respectively. Age, body mass index, smoking status, high blood pressure, diabetes mellitus, presence of tendon xanthomas, total cholesterol level, triglyceride levels, high-density lipoprotein cholesterol level, low-density lipoprotein cholesterol level, and Lp(a) did not differ among genotypes. The incidence of CVD and the age of onset of CVD did not differ among genotypes either. In the multivariant analysis, apo E genotype did not contribute significantly to CVD. CONCLUSIONS: Heterozygous men with FH have a very high risk of coronary disease in a Mediterranean country, and the apo E genotype in this large group of adults with FH is not associated either with CVD or lipid values, in contrast with the established effect in the general population.

A common variant in the ABCA1 gene is associated with a lower risk for premature coronary heart disease in familial hypercholesterolaemia.

Familial hypercholesterolaemia (FH) is a common autosomal codominant hereditary disease caused by defects in the LDL receptor (LDLR) gene, and one of the most common characteristics of affected subjects is premature coronary heart disease (CHD). In heterozygous FH patients, the clinical expression of FH is highly variable in terms of the severity of hypercholesterolaemia and the age of onset and severity of CHD. Identification of mutations in the ATP binding cassette transporter 1 (ABCA1) gene in patients with Tangier disease, who exhibit reduced HDL cholesterol and apolipoprotein A1 concentrations and premature coronary atherosclerosis, has led us to hypothesise that ABCA1 could play a key role in the onset of premature CHD in FH. In order to know if the presence of the R219K variant in the ABCA1 gene could be a protective factor for premature CHD in FH, we have determined the presence of this genetic variant by amplification by PCR and restriction analysis in a group of 374 FH subjects, with and without premature CHD. The K allele of the R219K variant was significantly more frequent in FH subjects without premature CHD (0.32, 95% CI 0.27 to 0.37) than in FH subjects with premature CHD (0.25, 95% CI 0.21 to 0.29) (p<0.05), suggesting that the genetic variant R219K in ABCA1 could influence the development and progression of atherosclerosis in FH subjects. Moreover, the K allele of the R219K polymorphism seems to modify CHD risk without important modification of plasma HDL-C levels, and it appears to be more protective for smokers than non-smokers.

A double mutant [N543H+2393del9] allele in the LDL receptor gene in familial hypercholesterolemia: effect on plasma cholesterol levels and cardiovascular disease.

Familial hypercholesterolemia is a genetic disorder caused by mutations in the LDL receptor gene. During a survey of mutations of LDL receptor gene in Spanish FH patients we found two mutations in the same allele: a missense N543H mutation in exon 11 and a 9bp inframe deletion (2393del9) located in exon 17. This double mutant allele was founded in 10 out of 458 unrelated patients: one homozygous FH [N543H+2393del9] + [N543H+2393del9], one compound heterozygote [N543H+2393del9] + [W-18X+E256K] and 8 heterozygotes. Flow cytometric analysis showed a defective LDL binding (20% of normal value) and internalization (23%) in lymphocytes from the homozygous patient; furthermore, studies of mitogen-stimulated lymphocytes demonstrated that the ability of LDL to support cell proliferation was impaired. Unexpectedly, not all carriers of the double mutant allele develop hypercholesterolemia and, furthermore, cholesterol-lowering treatment of the homozygous patient resulted in a 58% LDL cholesterol reduction. In conclusion, the phenotypic expression in the homozygous and heterozygous patients presented here, as well as the LDL-receptor residual activity, allowed the classification of this mutation as mild extending the group of mild mutations found at homozygosity.

Mutation analysis in 36 unrelated Spanish subjects with familial hypercholesterolemia: identification of 3 novel mutations in the LDL receptor gene.

We used the single strand conformation polymorphism (SSCP) method to investigate 36 apparently unrelated Spanish patients with familial hypercholesterolemia (FH) for mutations in the promoter region and the 18 exons and their flanking intron sequences of the low density lipoprotein receptor (LDLR) gene. Nineteen aberrant SSCP patterns were found, and the underlying mutations were characterized by DNA sequencing. In addition, we tested all patients for the presence of mutations in the gene coding for apolipoprotein B (apo B). Five missense mutations (Q71E, S156L, E256K, N543H and T705I), four nonsense mutations (W(-18)X, E10X, Q133X and C255X), six frameshift mutations (211delG, 518delG, 1045delC, 2085del19, 2207insT and 2393del9) and five splicing mutations (313+1G->C, 1061-8T->C, 1845+1G->C, 2140+5G->A and 2390-1G->C) were identified in the LDLR gene. In total, we detected 20 mutations, 3 of which, designated 1045delC, 1845+1G->C and 2207insT, have not been previously described. Seven patients were found to carry two different mutations in the same allele: W(-18)X and E256K (one patient), Q71E and 313+1G->C (two patients), 1061-8T->C and T705I (two patients), 518delG and 2140+5G->A (one patient) and N543H and 2393del9 (one patient). As we expected, there is a broad spectrum of mutations in the LDLR gene, given the genetic heterogeneity of the Spanish population.

Comparison of the hypolipidemic effect of gemfibrozil versus simvastatin in patients with type III hyperlipoproteinemia.

BACKGROUND: Type III hyperlipoproteinemia is characterized by the accumulation of chylomicron and very low density lipoprotein (VLDL) remnants. Individuals with this disorder have a high risk of premature atherosclerosis, and hypolipidemic drugs are useful in their management. METHODS: We compared, in a double-blind, placebo-controlled, randomized crossed study, the effects of gemfibrozil (1200 mg/day) and simvastatin (20 mg/day) on lipids, apolipoprotein AI, apolipoprotein B, and apolipoprotein E and on lipids and apolipoprotein B content in VLDL, intermediate-density lipoprotein (IDL), low-density lipoprotein (LDL), and high-density lipoprotein (HDL) in 10 patients with type III hyperlipoproteinemia. RESULTS: Levels of total cholesterol, VLDL cholesterol, IDL cholesterol, and apolipoprotein B decreased with both drugs. Larger reductions in triglycerides (109 +/- 28.2 mg/dL, P =.005), VLDL cholesterol (24.7 +/- 10.9 mg/dL, P =.05), and VLDL triglycerides (86.3 +/- 20.2 mg/dL, P =.003) were obtained with gemfibrozil compared with simvastatin. LDL cholesterol reduction was more effective with simvastatin than with gemfibrozil (44.3 +/- 17.1 mg/dL, P =.03). HDL cholesterol after gemfibrozil was 5.71 +/- 2.37 mg/dL higher than after simvastatin. CONCLUSIONS: In patients with type III hyperlipoproteinemia gemfibrozil is more effective in reducing total triglyceride and VLDL lipid levels than simvastatin, and simvastatin is better in reducing LDL cholesterol than gemfibrozil is. IDL and apolipoprotein E levels were reduced similarly with both drugs.

Association of polymorphisms at the SR-BI gene locus with plasma lipid levels and body mass index in a white population.

The scavenger receptor class B type I (SR-BI) is a lipoprotein receptor that has been shown to be important in high density lipoprotein cholesterol (HDL-C) metabolism in mice. To determine its role in humans, we have characterized the human SR-BI gene and investigated its genetic variation in 489 white men and women. Five variants were demonstrated: 2 in introns (3 and 5) and 3 in exons (1, 8, and 11). Three variants at exons 1 and 8 and intron 5 with allele frequencies >0.1 were used to examine associations with lipid or anthropometric variables. The exon 1 variant was significantly (P<0.05) associated with increased HDL-C and lower low density lipoprotein cholesterol (LDL-C) values in men, but no associations were observed in women. The exon 8 variant was associated in women with lower LDL-C concentrations (3.05+/-0.98 mmol/L and 3.00+/-0.93 mmol/L for heterozygotes and homozygotes, respectively) compared with women homozygous for the common allele (3.39+/-1.09 mmol/L, P=0. 043). No associations for this variant were observed in men. Women carriers of the intron 5 variant showed a higher body mass index (23. 8+/-3.8 kg/m2, P=0.031) than those women homozygous for the common allele (22.4+/-3.4 kg/m2). Similar results were observed after haplotype analysis. Multiple regression analysis using HDL-C, LDL-C, and body mass index as dependent variables and age, sex, and each of the genetic variants as predictors also provided similar results. The associations found with both LDL-C and HDL-C suggest that SR-BI may play a role in the metabolism of both lipoprotein classes in humans.

Beta-glucocerebrosidase gene locus as a link for Gaucher's disease and familial hypo-alpha-lipoproteinaemia.

BACKGROUND: Gaucher's disease is the most common lysosomal storage disorder, caused by deficiency of glucocerebrosidase resulting from homozygosity for any of several mutations of the glucocerebrosidase gene locus. Affected people have decreased concentrations of LDL cholesterol (LDL-C) and HDL cholesterol (HDL-C). We assessed the association between mutations in the glucocerebrosidase locus and hypo-alpha-lipoproteinaemia. METHODS: We studied 258 people from 43 unrelated Spanish families. 57 participants were affected, 137 were non-affected carriers, and 64 were non-carriers. We determined glucocerebrosidase genotypes and measured plasmid lipids, apolipoproteins A-I, B, and E, and leucocyte glucocerebrosidase activity. FINDINGS: The most common glucocerebrosidase mutations were N370S (45%), L444P (23%), and G377S (5%). Deletions and recombinants accounted for another 5%, and point mutations in exons 5, 6, 9, and 10 were present in 12%. Affected participants had lower LDL-C and HDL-C concentrations than non-affected carriers (p<0.001) and non-carriers (p<0.001). HDL-C values were also significantly different between the non-affected carriers and non-carriers. Mutations at this locus may account for as much as 19.5% of the genetic variability in HDL-C in the population studied. INTERPRETATION: Heterozygosity for these mutations at the glucocerebrosidase locus does not result in clinical expression of Gaucher's disease but can decrease HDL-C concentrations. Given the high frequency of these mutations, the glucocerebrosidase locus might lead to familial low alpha-lipoproteinaemia in up to 2% of the general population and be one of the most common known genetic causes of HDL-C.