Monogenic dyslipidemias: window on determinants of plasma lipoprotein metabolism.
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Animals↗
Biomedical subjects
R A Hegele
Publications and source records attributed to R A Hegele.
Premature atherosclerosis associated with monogenic insulin resistance.
BACKGROUND: The common insulin resistance syndrome, with obesity, dyslipidemia, hyperglycemia, and hypertension, is associated with increased risk of atherosclerosis. Early atherosclerosis in rare monogenic forms of insulin resistance, however, has not been extensively documented. Cardiovascular end points were thus evaluated in subjects with Dunnigan-type familial partial lipodystrophy (FPLD) due to mutations at LMNA codon 482. METHODS AND RESULTS: FPLD subjects >/=35 years old were stratified by genotype for either the LMNA R482Q or R482W mutation. Twenty-three subjects were heterozygous mutation carriers, and 17 were R482/R482 homozygous family control subjects. All LMNA mutation carriers had FPLD with insulin resistance. In addition, LMNA mutation carriers had significantly more type 2 diabetes, hypertension, and dyslipidemia than normal family control subjects. Eight LMNA mutation carriers had coronary heart disease (CHD), compared with 1 normal control subject (OR 5.9, 95% CI 1.2 to 30.2). Six LMNA mutation carriers had CHD end points before age 55 years, and 4 of these, all women, had been hospitalized for CABG surgery between the ages of 35 and 54 years. CONCLUSIONS: Rare LMNA mutations that underlie FPLD with insulin resistance and hyperinsulinemia are also associated with early CHD, notably in women. This suggests that abnormalities of the nuclear envelope can result in a phenotype that recapitulates most of the important attributes of the common insulin resistance syndrome, including accelerated cardiovascular disease. FPLD thus appears to be an appropriate human monogenic model for the common insulin resistance syndrome.
Age Distribution↗
Variable association between genetic variation in the CYP7 gene promoter and plasma lipoproteins in three Canadian populations.
The promoter sequence variant -278A in the CYP7 gene, which encodes cholesterol 7-alpha hydroxylase, was previously reported to be associated with reduced plasma low density lipoprotein (LDL) cholesterol concentration. We tested for association of CYP7-278A with plasma lipoprotein traits in samples taken from three distinct Canadian populations: 594 Alberta Hutterites, 325 Ontario Oji-Cree and 190 Keewatin Inuit. The CYP7-278A allele frequencies in these three groups were 0.708, 0.466 and 0.490, respectively. The frequencies of CYP7-278A/A homozygotes were 0.481, 0.215 and 0.247, respectively. In the Hutterites, CYP7-278A was associated with reduced plasma HDL-cholesterol and apolipoprotein AI concentration. In the Oji-Cree, CYP7-278A was not significantly associated with any plasma lipoprotein trait. In the Inuit CYP7-278A was associated with elevated plasma total and LDL-cholesterol. There was no consistent relationship between the population mean plasma LDL-cholesterol concentration and the population CYP7-278A frequency. Our findings suggest that the common -278A promoter variant of CYP7 was inconsistently associated with variation in plasma LDL- and HDL-cholesterol in samples from three independent populations. The inconsistencies could be due to differences in genetic background or to unspecified environmental or genetic factors.
Adult↗
Low density lipoprotein receptor (LDLR) gene mutations in Canadian subjects with familial hypercholesterolemia, but not of French descent.
Heterozygous familial hypercholesterolemia (FH) is a relatively common autosomal dominant disorder, which is characterized by elevated plasma concentrations of low density lipoprotein (LDL) cholesterol and early coronary heart disease. FH results from mutations in the gene encoding the LDL receptor (LDLR). In Canada, there is a founder effect for LDLR mutations in FH among individuals of French descent, most of whom reside in the province of Quebec. However, the spectrum of mutations in other regions, specifically in the populous and predominantly English-speaking province of Ontario, has not been studied. We sequenced the coding regions, promoter and intron-exon boundaries of the LDLR gene in 60 Ontario FH subjects from a variety of ethnic backgrounds other than French Canadian. We found 25 LDLR mutations in 34 subjects. Eleven LDLR mutations were novel, including two in-frame deletions of a single amino acid (one each in exons 2 and 4), two larger deletions that shifted the reading frame (one each in exons 4 and 10), five missense mutations (C42R, A370T, T413M, L561P and E760D) and two splice acceptor mutations (one each in introns 3 and 8). The results indicate that FH is more genetically diverse in Ontario than in Quebec. The results are also consistent with findings from investigations of the LDLR in FH conducted in other countries, in which PCR-based, exon-by-exon sequencing uncovers small mutations in about half of the subjects screened. The gap in molecular diagnosis suggests that lesions not found by this sequencing strategy, such as larger scale LDLR mutations that cannot be amplified, may underlie a substantial number of cases of FH. Alternatively, there might be genetic heterogeneity underlying the FH phenotype, with contributions from other single or multiple genes. Hum Mutat 18:359, 2001.
DNA Mutational Analysis↗
ABCC6 gene polymorphism associated with variation in plasma lipoproteins.
The ATP cassette-binding (ABC) gene superfamily contains more than 40 members, many of which are involved in cellular lipid transport. The most prominent example is ABCA1, mutations in which affect plasma high-density lipoprotein (HDL) cholesterol concentration. ABCC6 is another member of the ABC gene family, and mutations in ABCC6 were recently shown to cause pseudoxanthoma elasticum (PXE). A Canadian patient with PXE was referred for assessment of moderately severe type IV hyperlipoproteinemia with hypoalphalipoproteinemia, which was refractory to pharmacological treatment. We identified intron-exon boundaries of ABCC6 to sequence genomic DNA from this patient to find the disease mutation. We report (1) identification of a set of amplification primers for the 31 exons of ABCC6; (2) identification of the ABCC6 R>X1164 nonsense mutation in the PXE subject with dyslipidemia; (3) identification of common amino acid variants and silent nucleotide variants in ABCC6, with a range of allele frequencies across ethnic groups; (4) evidence consistent with a possible pseudogene encoding 9 exons with sequence homology to ABCC6; and (5) association of the ABCC6 R>Q1268 variant with plasma triglyceride and HDL cholesterol. The results suggest that ABCC6 may be a determinant of plasma lipoproteins.
Adult↗
Single-nucleotide polymorphisms of the proprotein convertase subtilisin/ kexin type 5 (PCSK5) gene.
The proprotein convertase. subtilisin/kexin type 5, or PCSK5, mediates post-translational endoproteolytic processing for several integrin alpha subunits. We identified two silent single-nucleotide polymorphisms (SNPs) in PCSK5, which were found to vary in frequency across ethnic groups. The identification of these amplification primers and SNPs provides tools to investigate PCSK5 for association with inflammatory or vascular phenotypes.
Alleles↗
Single nucleotide polymorphisms of the resistin (RSTN) gene.
Type 2 diabetes mellitus is a complex phenotype that is frequently associated with central obesity and insulin resistance. Recently, a protein named resistin, encoded by RSTN (OMIM #605565), was identified in adipose tissue. Serum resistin was elevated in obese and diabetic mice, and administration of resistin to normal mice was found to interfere with glucose tolerance and insulin action. Because of these functions, resistin is a candidate gene for diabetes and obesity. Through the use of DNA sequencing, we thus developed amplification primers for rapid screening of the RSTN gene that encodes resistin. No putative mutations were found, but two noncoding single-nucleotide polymorphisms (SNPs) were identified, and these were found to vary in frequency across various ethnic groups. The identification of amplification primers and SNPs provides tools to investigate resistin for association with other phenotypes.
Base Sequence↗
Single nucleotide polymorphisms of the fukutin gene.
Mutations in the LMNA gene, which encodes nuclear lamins A and C, underlie both Emery-Dreifuss muscular dystrophy (EMD2) and Dunnigan-type familial partial lipodystrophy (FPLD). This indicates that one gene can cause different phenotypes characterized by tissue degeneration. The gene for one form of Berardinelli-Seip-type congenital total lipodystrophy (BSCL) has been mapped to chromosome 9q34. Based on the observation that one gene caused both FPLD and EMD2, we considered that a known gene for muscular dystrophy at or near the BSCL locus on chromosome 9q would be an appropriate candidate for BSCL. The gene encoding fukutin, which is mutated in Fukuyama congenital muscular dystrophy has been mapped to 9q31. We thus developed amplification primers for the coding regions of the fukutin gene. We found no putative disease mutations, but through screening of diseased and normal subjects, we identified three novel single nucleotide polymorphisms (SNPs). We conclude that mutations in fukutin are not present in subjects with BSCL. However, the identification of SNPs provides tools to investigate this protein for association with other phenotypes.
Base Sequence↗
Single nucleotide polymorphisms of the very low density lipoprotein receptor (VLDLR) gene.
The very low density lipoprotein receptor (VLDLR) has a potentially important role in lipoprotein metabolism and Alzheimer's disease. We developed amplification primers for most of the coding region and 3'-untranslated region of VLDLR and used sequencing of genomic DNA to examine these regions of VLDLR in subjects with familial combined hyperlipidemia and in normal controls. We identified ten novel single nucleotide polymorphisms (SNPs) for VLDLR. We also found one rare coding sequence variant, S>R153, in a subject with familial combined hyperlipidemia, which was absent from 2360 normal alleles. The identification of intron-exon boundaries, amplification primers, and SNPs provides tools to investigate VLDLR for genetic association and linkage studies.
3' Untranslated Regions↗
Single nucleotide polymorphisms of RXRA encoding retinoid X receptor alpha.
Retinoic X receptor alpha (RXRA), encoded by RXRA, plays a key role in development and metabolism, specifically in adipocyte biology, glucose homeostasis, and intestinal cholesterol balance. RXRA is also a positional candidate gene for Berardinelli-Seip congenital lipodystrophy. We report the systematic screening of RXRA coding regions by genomic DNA sequencing, which has resulted in the identification of three novel single-nucleotide polymorphisms.
3' Untranslated Regions↗
Polymorphisms in PNLIP, encoding pancreatic lipase, and associations with metabolic traits.
Pancreatic lipase (EC 3.1.1.3) is an exocrine secretion that hydrolyzes dietary triglycerides in the small intestine. We developed genomic amplification primers to sequence the 13 exons of PNLIP, which encodes pancreatic lipase, in order to screen for possible mutations in cell lines of four children with pancreatic lipase deficiency (OMIM 246600). We found no missense or nonsense mutations in these samples, but we found three silent single-nucleotide polymorphisms (SNPs), namely, 96A/C in exon 3, 486C/T in exon 6, and 1359C/T in exon 13. In 50 normolipidemic Caucasians, the PNLIP 96C and 486T alleles had frequencies of 0.083 and 0.150, respectively. The PNLIP 1359T allele was absent from Caucasian, Chinese, South Asian, and North American aboriginal samples, but had a frequency of 0.085 in an African sample, suggesting that it is a population-specific variant. In an association analysis of 185 African neonates, the PNLIP 1359C/T SNP genotype was significantly associated with concentrations of plasma lipoproteins. These associations were most likely due to linkage disequilibrium with another functional variant at or near PNLIP. Thus, we report three new SNPs for the PNLIP, which may serve as markers for association analyses and for pharmacogenetic studies of pancreatic lipase inhibitors.
Africa↗
Single-nucleotide polymorphisms of the nuclear lamina proteome.
Familial partial lipodystrophy (FPLD) has been shown to be due to mutations in the LMNA gene encoding nuclear lamins A and C, indicating that defective structure of the nuclear envelope can produce this unique phenotype. Some patients with inherited partial lipodystrophy have normal LMNA coding, promoter, and 3'-untranslated region sequences. This suggests that the FPLD phenotype is genetically heterogeneous. Among the candidate genes to consider for the non-LMNA-associated forms of FPLD are other components of the inner nuclear membrane, such as lamin B1 and B2 and the lamin B receptor. We developed amplification primers for the coding regions of LMNB1, LMNB2, and LBR, which encode lamin B1, lamin B2, and the lamin B receptor, respectively. We found no putative disease mutations in any of these proteins in subjects with non-LMNA FPLD, but, through the screening of diseased and normal subjects, we identified several single-nucleotide polymorphisms (SNPs); specifically, five SNPs in LMNB1 and four SNPs in LBR. The LMNB2 gene was monomorphic in screening experiments. We conclude that mutations in other constituent proteins of the nuclear envelope are not present in subjects with non-LMNA-associated FPLD. However, the identification of amplification primers and SNPs provides tools to investigate these proteins for their association with other phenotypes.
Base Sequence↗
Evidence for expanded clinical utility of statin drugs.
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Coronary Disease↗
Genes and environment in type 2 diabetes and atherosclerosis in aboriginal Canadians.
The incidence of coronary heart disease (CHD) among aboriginal people in northern Ontario has tripled over the past 20 years. This is inextricably linked to the remarkably high prevalence of type 2 diabetes in these native communities. Approximately 40% of the Oji-Cree of northern Ontario have typical obesity-related type 2 diabetes, which represents a drastic increase from virtually unreportable levels 50 years ago. The Oji-Cree have a private mutation in the HNF1A gene, namely G319S, which is absent from other ethnic groups and aboriginal populations. The most compelling reasons that HNF1A S319 is a diabetes-susceptibility allele are its consistent statistical association with the presence and severity of diabetes. Also, HNF1A S319 has specificity and positive predictive values of 97% and 95%, respectively, for the development of diabetes in the Oji-Cree by 50 years of age. This makes the HNF1A G319S genotype the most specific predictive genetic test for diabetes in any human population. HNF1A S319 has all the attributes of a thrifty allele in the Oji-Cree. It is possible that the recent increase in CHD in the aboriginal people of northern Ontario is the result of the expression of diabetes susceptibility due to HNF1A S319 as a consequence of rapid changes in environment and lifestyle.
American Indian or Alaska Native↗
Lecithin:cholesterol acyl transferase G30S: association with atherosclerosis, hypoalphalipoproteinemia and reduced in vivo enzyme activity.
OBJECTIVES: A 69 yr old male was referred for assessment of a very low plasma HDL cholesterol and apolipoprotein AI concentration. At age 65, he had undergone triple vessel coronary bypass graft surgery. He had a strong family history of early coronary heart disease. We analyzed the molecular basis of his clinical and biochemical abnormalities. DESIGN AND METHODS: We used DNA sequencing to determine whether mutations in LCAT were present. We also evaluated plasma biochemistry and LCAT activity. RESULTS: DNA sequencing revealed that the patient was a heterozygote for the G30S mutation in the gene encoding lecithin:cholesteol acyl transferase (LCAT). His plasma was found to have half-normal LCAT activity. CONCLUSIONS: The findings in this patient suggest that rare dysfunctional mutations in candidate genes, such as LCAT, can contribute to the spectrum of patients ascertained because of low HDL cholesterol.
Aged↗
Cholesterol and apolipoprotein B metabolism in Tangier disease.
Tangier disease (TD), caused by mutations in the gene encoding ATP-binding cassette 1 (ABCA1), is a rare genetic disorder in which homozygotes have a marked deficiency of high density lipoproteins (HDL), as well as concentrations of low density lipoproteins (LDL) that are typically 40% of normal. Although it is well known that the reduced levels of HDL in TD are due to hypercatabolism, the mechanism responsible for the low LDL levels has not been defined. Recently, it has been reported that intestinal cholesterol absorption is altered in ABCA1 deficient mice, suggesting that aberrant cholesterol metabolism may contribute to the LDL reductions in TD. In order to explore this possibility, as well as to define the role that ABCA1 plays in the metabolism of apolipoprotein (apoB)-containing lipoproteins, we determined the kinetics of apoB-100 within lipoproteins, and cholesterol absorption, biosynthesis, and turnover, in a compound heterozygote for TD. The levels of HDL cholesterol, LDL cholesterol and LDL apoB-100 in this subject were 7, 27 and 69% of normal, respectively, the latter of which was due to a two-fold increase in LDL catabolism (0.54 vs. 0.26+/-0.07 poolsday(-1)) relative to controls (n=11). NMR analysis of plasma lipoproteins revealed that 91% of the LDL cholesterol in the TD subject was contained within small, dense LDL, as compared with only 20% for controls (n=70). Cholesterol absorption was 97% of the value for controls (n=15) in the TD subject, at 45%, with cholesterol synthesis and turnover increased modestly by 17 and 25%, respectively. Our data are consistent with the concept that the reductions of LDL observed in TD are due to enhanced catabolism, secondary to changes in LDL composition and size, with neither cholesterol absorption nor metabolism significantly influenced by mutations in ABCA1.
ATP Binding Cassette Transporter 1↗
Molecular basis of partial lipodystrophy and prospects for therapy.
Lipodystrophy is characterized by altered partition of adipose tissue. Despite heterogeneous causes, which include genetic, autoimmune and drug-induced forms, lipodystrophy syndromes have similar metabolic attributes, including insulin resistance, hyperlipidemia and diabetes. The mechanisms underlying the insulin resistance are unknown. One form of lipodystrophy, namely Dunnigan-type familial partial lipodystrophy (FPLD) was shown to result from mutations in the LMNA gene, which encodes nuclear lamins A and C. Although the relationship between the mutations in the nuclear envelope and insulin resistance is unclear at present, these findings might eventually be shown to have relevance for the common insulin resistance syndrome and for drug-associated lipodystrophies.
Endopeptidases↗
Genetic determinants of type 2 diabetes mellitus.
Type 2 diabetes refers to a group of disparate metabolic diseases, which are typically characterized by insulin resistance in peripheral tissues, together with impaired insulin secretion from pancreatic beta-cells. The complexity of type 2 diabetes is related to factors such as genetic heterogeneity, interactions between genes, and the modulating role played by the environment. Recent progress has included defining the molecular basis of monogenic forms of type 2 diabetes, such as familial partial lipodystrophy and the subtypes of maturity-onset diabetes of the young (MODY), and also the identification of chromosomal regions that may harbor type 2 diabetes susceptibility genes. Many common variants in functional and positional candidate genes, including ADRB3, PPARG, ENPP1, and CAPN10, have also been studied for their possible role as determinants of type 2 diabetes, with varying levels of agreement between studies. The availability of a relatively complete sequence of the human genome will increase the amount of genetic information that can be used to evaluate hypotheses for the genetic basis of type 2 diabetes. To make sense of human type 2 diabetes in the post-genomic era, it is essential to have well-defined phenotypes in addition to sufficient numbers of individuals with the appropriate pedigree structure from families and/or communities.
Animals↗