Leif Groop

The aim of the study was to evaluate the relationship between insulin sensitivity, beta cell function and glucose tolerance, and its dependence on variants in the newly identified Type 2 diabetes susceptibility gene, calpain-10 (CAPN10).

To determine the impact of a family history of the common form of type 2 diabetes and the phenotype of the proband on anthropometric and metabolic variables in normoglycemic first-degree relatives, we studied 2,100 first-degree relatives of patients with the common form of type 2 diabetes (FH+) and 388 subjects without a family history of diabetes (FH–). All subjects participated in an oral glucose tolerance test to allow measurement of insulin secretion [30-min incremental insulin/glucose (I/G 30)] and insulin sensitivity [homeostasis model assessment (HOMA) of insulin resistance (IR)]. A subset participated in a euglycemic clamp (n = 75) and an intravenous glucose tolerance test (n = 300). To study the effect of a particular phenotype of the proband, insulin secretion and sensitivity were also compared between first-degree relatives of diabetic probands with high and low waist-to-hip ratio (WHR) and probands with early and late onset of diabetes. FH+ subjects were more insulin resistant, as seen from a higher HOMA-IR index (P = 0.006) and a lower rate of insulin-stimulated glucose uptake (P = 0.001) and had more features of the metabolic syndrome (P = 0.02, P = 0.0002) compared with FH– subjects. Insulin secretion adjusted for insulin resistance (disposition index, DI) was also lower in the FH+ vs. FH– subjects (P = 0.04). Relatives of diabetic probands with a high WHR had reduced insulin-mediated glucose uptake compared with relatives of probands with a low WHR (P = 0.04). Relatives of diabetic patients with age at onset P < 0.005) and lower DI (P < 0.005) than relatives of patients with age at onset >65 yr (highest quartile). We conclude that early age at onset of type 2 diabetes and abdominal obesity have a significant influence on the metabolic phenotype in the nondiabetic first-degree relative.

Positional cloning is expected to identify novel susceptibility genes underlying complex traits, but replication of genome-wide linkage scan findings has proven erratic. To improve our ability to detect and prioritize chromosomal regions containing type 2 diabetes susceptibility genes, the GIFT consortium has implemented a meta-analysis of four scans conducted in European samples. These included the Botnia I and Botnia II scans, with respectively 58 and 353 pedigrees from Finland and Sweden, the Warren 2 scan performed in 573 multiplex sibships from the UK, and a scan of 143 families from France. The meta-analysis was implemented using the genome-search analysis method (GSMA), an exploratory data analysis technique which is robust across study designs. The analysis provided evidence for linkage of type 2 diabetes to six regions, with the strongest evidence on chromosome 17p11.2–q22 ( P =0.0016), followed by 2p22.1–p13.2 ( P =0.027), 1p13.1–q22 ( P =0.028), 12q21.1–q24.12 ( P =0.029), 6q21–q24.1 ( P =0.033) and 16p12.3–q11.2 ( P =0.033). Linkage analysis of the pooled raw genotype data generated maximum LOD scores in the same regions as identified by GSMA. Altogether, our results have indicated that GSMA is a valuable tool to identify chromosomal regions of interest and that accumulating evidence for linkage from small peaks detected across several samples may be more important than getting a high peak in a single sample. This meta-analysis has led to identification of a novel region on chromosome 17 linked to type 2 diabetes; this region has not been highlighted in any published scan to date but on the basis of these data justifies further exploration.

In an attempt to identify novel susceptibility genes predisposing to early-onset diabetes (EOD), we performed a genome-wide scan using 433 markers in 222 individuals (119 with diabetes) from 29 Scandinavian families with ≥2 members with onset of diabetes ≤45 years. The highest nonparametric linkage (NPL) score, 2.7 (P < 0.01), was observed on chromosome 1p (D1S473/D1S438). Six other regions on chromosomes 3p, 7q, 11q, 18q, 20q, and 21q showed a nominal P value P < 0.01) and 16q (D16S419; NPL 2.9; P < 0.01). After exclusion of three families with MODY1, MODY3, and mitochondrial mutations, the highest NPL scores were observed on chromosomes 1p (D1S438; NPL 2.6; P < 0.01), 3p (D3S1620; NPL 2.2; P < 0.03), 5q (D5S1465; NPL 2.1; P < 0.03), 7q (D7S820; NPL 2.0; P < 0.03), 18q (D18S535; NPL 1.9; P < 0.04), 20q (D20S195; NPL 2.5; P < 0.02), and 21q (D21S1446; NPL 2.2; P < 0.03). We conclude that considerable heterogeneity exists in Scandinavian subjects with EOD; 24% had MODY or maternally inherited diabetes and deafness, and ∼60% were GAD antibody positive or had type 1 diabetes-associated HLA genotypes. Our data also point at putative chromosomal regions, which could harbor novel genes that contribute to EOD.

In a previous study, we identified suggestive linkage between type 2 diabetes and a locus on chromosome 9p13-q21. This region contains the gene annexin I (ANXA1), encoding a protein suggested to be involved in both insulin secretion and insulin action. In this study, we sequenced the exon/intron boundaries of the human ANXA1 gene and performed mutation screening in 41 individuals from the initial linkage study. We identified five single nucleotide polymorphisms A58G, A401G, intronic variance sequence (IVS)8-28A/G, IVS11 +31A/G, and IVS12-11T/G, which were further tested for association to diabetes in 197 parent/offspring trios using the transmission disequilibrium test. No significant association with type 2 diabetes was observed, although the common A allele of the +58A/G variant gave a 22:12 transmission distortion (P = 0.12). This variant was further genotyped in 481 case and control subjects, but no difference in allele, genotype, or haplotype frequencies were observed between the groups. Further, a novel polymorphic (CA)_15–25 repeat in intron 11 was genotyped in the subjects included in the initial linkage study. No improvement of the original finding was observed. We therefore concluded that the ANXA1 gene is unlikely to harbor variants that contribute to risk of type 2 diabetes.

Groop L, Orho‐Melander M (Wallenberg Laboratory, Lund University, Malmö, Sweden). The dysmetabolic syndrome. J Intern Med 2001; 250: 105–120.The first unifying definition for the metabolic syndrome was proposed by WHO in 1998. In accordance to this, patients with type 2 diabetes mellitus or impaired glucose tolerane have the syndrome if they fulfil two of the criteria: hypertension, dyslipidaemia, obesity/abdominal obesity and microalbuminuria. Persons with normal glucose tolerance (NGT) should also be insulin resistant. About 40% of persons with impaired glucose tolerance (IGT) and 70% of patients with type 2 diabetes have features of the syndrome. Importantly, presence of the dysmetabolic syndrome is associated with reduced survival, particularly because of increased cardiovascular mortality. The dysmetabolic syndrome most likely results from interplay between several genes and an affluent environment. Compatible with the thrifty gene theory, common variants in genes regulating lipolysis, thermogenesis and glucose uptake in skeletal muscle account for a large part of such thrifty genes. However, hitherto unknown genes may still be identified by random gene approaches.

Aims   To assess the effect of metformin on insulin sensitivity, glucose tolerance and components of the metabolic syndrome in patients with impaired glucose tolerance (IGT).Methods   Forty first‐degree relatives of patients with Type 2 diabetes fulfilling WHO criteria for IGT and participating in the Botnia study in Finland were randomized to treatment with either metformin 500 mg b.i.d. or placebo for 6 months. An oral glucose tolerance test (OGTT) and a euglycaemic hyperinsulinaemic clamp in combination with indirect calorimetry was performed at 0 and 6 months. The patients were followed after stopping treatment for another 6 months in an open trial and a repeat OGTT was performed at 12 months.Results   Metformin treatment resulted in a 20% improvement in insulin‐stimulated glucose metabolism (from 28.7 ± 13 to 34.4 ± 10.7 µmol/kg fat‐free mass (FFM)/min) compared with placebo (P = 0.01), which was primarily due to an increase in glucose oxidation (from 16.6 ± 3.6 to 19.1 ± 4.4 µmol/kg FFM; P = 0.03) These changes were associated with a minimal improvement in glucose tolerance, which was maintained after 12 months.Conclusions   Metformin improves insulin sensitivity in subjects with IGT primarily by reversal of the glucose fatty acid cycle. Obviously large multicentre studies are needed to establish whether these effects are sufficient to prevent progression to manifest Type 2 diabetes and associated cardiovascular morbidity and mortality.Diabet. Med. 18, 578–583 (2001)

—To address the question of whether elevated concentrations of nonesterified fatty acids (NEFAs) are associated with an increased risk of cardiovascular disease, we measured NEFA concentrations in 140 diabetic and 343 nondiabetic unrelated Swedish subjects with a family history of type 2 diabetes and related the findings to history of cardiovascular disease in their parents. Parents of nondiabetic offspring belonging to the quartile of highest NEFA concentrations had a higher risk of myocardial infarction (35% versus 16%, P P <0.0005) than did parents of offspring from the lowest NEFA quartile. In a multiple logistic regression analysis, a high NEFA concentration in offspring was significantly associated with myocardial infarction and stroke in their parents. No such relationship was observed between diabetic offspring and their parents. Assuming that the same relationship between NEFA concentrations and cardiovascular disease is seen in the offspring and their parents, the findings suggest that elevated NEFA concentration is a risk factor for cardiovascular disease and could be pathogenically involved in the atherosclerotic process.