Recently, two G-->A polymorphisms at positions -308 and -238, in the promoter of the tumor necrosis factor alpha (TNF-alpha) gene, have been identified. These variants have, in different ethnic groups, been linked to estimates of insulin resistance and obesity. The objective of the present study was to investigate whether these genetic variants of TNF-alpha were associated with features of the insulin resistance syndrome or alterations in birth weight in two Danish study populations comprising 380 unrelated young healthy subjects and 249 glucose-tolerant relatives of type 2 diabetic patients, respectively. All study participants underwent an iv glucose tolerance test with the addition of tolbutamide after 20 min. In addition, a number of biochemical and anthropometric measures were performed on each subject. The subjects were genotyped for the polymorphisms by applying PCR restriction fragment length polymorphism. Neither of the variants was related to altered insulin sensitivity index or other features of the insulin resistance syndrome (body mass index, waist to hip ratio, fat mass, fasting serum lipids or fasting serum insulin or C-peptide). Birth weight and the ponderal index were also not associated with the polymorphisms. In conclusion, although the study was carried out on sufficiently large study samples, the study does not support a major role of the -308 or -238 substitutions of the TNF-alpha gene in the pathogenesis of insulin resistance or altered birth weight among Danish Caucasian subjects.
The -250G>A promoter variant in hepatic lipase associates with elevated fasting serum high-density lipoprotein cholesterol modulated by interaction with physical activity in a study of 16,156 Danish subjects.
CONTEXT: Hepatic lipase plays a pivotal role in the metabolism of high-density lipoprotein (HDL) and low-density lipoprotein by involvement in reverse cholesterol transport and the formation of atherogenic small dense low-density lipoprotein. OBJECTIVES: The objective was to investigate the impact of variants in LIPC on metabolic traits and type 2 diabetes in a large sample of Danes. Because behavioral factors influence hepatic lipase activity, we furthermore examined possible gene-environment interactions in the population-based Inter99 study. DESIGN: The LIPC -250G>A (rs2070895) variant was genotyped in the Inter99 study (n = 6070), the Anglo-Danish-Dutch Study of Intensive Treatment in People with Screen Detected Diabetes in Primary Care Denmark screening cohort of individuals with risk factors for undiagnosed type 2 diabetes (n = 8662), and in additional type 2 diabetic patients (n = 1,064) and glucose-tolerant control subjects (n = 360). RESULTS: In the Inter99 study, the A allele of rs2070895 associated with a 0.057 mmol/liter [95% confidence interval (CI) 0.039-0.075] increase in fasting serum HDL-cholesterol (HDL-c) (P = 8 x 10(-10)) supported by association in the Anglo-Danish-Dutch Study of Intensive Treatment in People with Screen Detected Diabetes in Primary Care study [0.038 mmol/liter per allele (95% CI 0.024-0.053); P = 2 x 10(-7)). The allelic effect on HDL-c was modulated by interaction with self-reported physical activity (P(interaction) = 0.002) because vigorous physically active homozygous A-allele carriers had a 0.30 mmol/liter (95% CI 0.22-0.37) increase in HDL-c compared with homozygous G-allele carriers. CONCLUSIONS: We validate the association of LIPC promoter variation with fasting serum HDL-c and present data supporting an interaction with physical activity implying an increased effect on HDL-c in vigorous physically active subjects carrying the -250 A allele. This interaction may have potential implications for public health and disease prevention.
AIMS/HYPOTHESIS: Adiponectin is an adipocytokine with lowered blood levels in obesity and Type 2 diabetes mellitus. We sought to define the specific effects of different alleles of the gene encoding adiponectin. METHODS: We studied the associations of adiponectin gene sequence variations with body fat distribution and insulin indices in 503 White and 276 Black subjects of the HERITAGE Family Study cohort and subjects from a Finnish population. RESULTS: The His111 allele frequency of the Tyr111 His polymorphism in Finnish Type 2 diabetic subjects (n=254) was higher (5.1%) than in control subjects (n=270) (2.6%; P = 0.033). In the HERITAGE cohort, the His111 allele was associated with a lower insulin sensitivity index (P = 0.018) and a higher acute insulin response to glucose (P = 0.0098) in Whites. Other variants showed associations with adiposity and plasma lipid values only in Blacks. Among Blacks, the IVS2+G62T variant was associated with body fat (P = 0.002) and total cholesterol values (P = 0.005), and the Gly15Gly variant with cholesterol (P = 0.009) and triglyceride (P = 0.05) levels. The haplotype derived from these two polymorphisms was associated with total body fat, while the IVS2+G62T and Tyr111His-haplotype was associated with body fat and disposition index. CONCLUSIONS: The carriers of the His111 allele may have a higher risk of developing Type 2 diabetes mellitus. Racial differences were found between Blacks and Whites in body composition and lipids according to ACDC genotypes. Sequence variants in the adiponectin gene appear to be associated with diabetes and diabetes-related phenotypes.
We describe a family with three cases of "clinically incomplete mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes (MELAS) syndrome" in which heteroplasmic tRNA(Leu(UUR)) mutation at nucleotide 3243 of the mitochondrial DNA was present in three generations. The amount of mutant genome varied among tissues: it was 60% in the kidney, 72% in the cardiac muscle, and 91% in the liver of the female proband's affected brother and 63% in the kidney, 71% in the cardiac muscle, and 71% in the liver of the female proband's perinatally deceased son. The tRNA(Leu(UUR)) mutation was also carried by the siblings of the proband's affected mother. None of them had any clinical signs of MELAS syndrome. This syndrome has the new feature of being associated with adult-onset diabetes mellitus, neurosensory hearing loss, and short stature.
Linkage studies have mapped loci for diabetic nephropathy and associated phenotypes on chromosome 3q. We studied 14 plausible candidate genes in the linkage region because of their potential role in vascular complications. In a large-scale study of patients from Denmark, Finland, and France who have type 1 diabetes, 1,057 case and 1,127 control subjects, as well as 532 trios, were investigated for association with diabetic nephropathy. We analyzed 69 haplotype-tagging single nucleotide polymorphisms and nonsynonymous variants that were identified by sequencing. Polymorphisms in three genes, glucose transporter 2 (SLC2A2), kininogen (KNG1), and adiponectin (ADIPOQ), showed nominal association with diabetic nephropathy in single-point analysis. The T-allele of SLC2A2_16459CT was associated with a decreased risk of diabetic nephropathy (odds ratio 0.79 [95% CI 0.66-0.96], P = 0.016), whereas the T-allele of KNG_7965CT and the A-allele of ADIPOQ_prom2GA were associated with increased risk of nephropathy (1.17 [1.03-1.32], P = 0.016; 1.46 [1.11-1.93], P = 0.006, respectively). Analyses of the transmission disequilibrium test showed similar trends only for ADIPOQ_prom2GA with the overtransmission of the A-allele to patients with diabetic nephropathy (1.52 [0.86-2.66], P = NS) and of the G-allele to patients without diabetic nephropathy (0.50 [0.27-0.92], P = 0.026). The overall significance for this variant (nominal P = 0.011) suggests that ADIPOQ might be involved in the development of diabetic nephropathy.
Lamin A/C (LMNA) is located within a region on chromosome 1q that has been linked with Type II (non-insulin-dependent) diabetes mellitus in Pima Indians. Rare mutations in exon 8 of LMNA underlie Dunnigan-Type familial partial lipodystrophy, a disease characterized by regional adipocyte degeneration and frequently accompanied by insulin resistance, glucose intolerance, and diabetes. A more common variant in exon 10 (3408C/T) has recently been associated with obesity in non-diabetic aboriginal Canadian subjects. Because obesity is a strongly predisposing factor for Type II diabetes, we hypothesized that the LMNA 3408C/T variant could be associated with diabetes and body mass index in Pima Indians.
To determine whether the LMNA 3408C/T variant contributes to Type II diabetes susceptibility, we genotyped the polymorphism in 1,338 Pimas using allelic discrimination technology. The locus was screened for additional variants in 20 diabetic Pima Indians and non-diabetic Pima Indians using denaturing high performance liquid chromatography and dideoxy sequencing.
We found no evidence for association of 3408C/T with diabetes, body mass index, total cholesterol, HDL cholesterol, triglycerides, leptin concentrations, or indices of insulin sensitivity and secretion. Subsequent screening of the remaining LMNA exons and flanking sequences revealed only rare variants in intron 4 and the 3'UTR, showing no frequency differences between diabetic and non-diabetic Pima Indians. We reassessed the linkage with diabetes following adjustment for the LMNA 3408C/T variant; adjustment for the effects of LMNA did not substantially modify the evidence for linkage.
We conclude that the LMNA 3408C/T variant probably does not play a role in susceptibility to diabetes or obesity in Pima Indians.
It has been proposed that type 1 and 2 diabetes might share common pathophysiological pathways and, to some extent, genetic background. However, to date there has been no convincing data to establish a molecular genetic link between them. We have genotyped three single nucleotide polymorphisms associated with type 2 diabetes in a large type 1 diabetic family collection of European descent: Gly972Arg in the insulin receptor substrate 1 (IRS1) gene, Glu23Lys in the potassium inwardly-rectifying channel gene (KCNJ11), and Pro12Ala in the peroxisome proliferative-activated receptor gamma2 gene (PPARG2). We were unable to confirm a recently published association of the IRS1 Gly972Arg variant with type 1 diabetes. Moreover, KCNJ11 Glu23Lys showed no association with type 1 diabetes (P > 0.05). However, the PPARG2 Pro12Ala variant showed evidence of association (RR 1.15, 95% CI 1.04-1.28, P = 0.008). Additional studies need to be conducted to confirm this result.