Hiroto Furuta

Mutations in the hepatocyte nuclear factor-1α gene in maturity-onset diabetes of the young (MODY3)

THE disease maturity-onset diabetes of the young (MODY) is a genetically heterogeneous monogenic form of non-insulin-dependent (type 2) diabetes mellitus (NIDDM), characterized by early onset, usually before 25 years of age and often in adolescence or childhood, and by autosomal dominant inheritance1. It has been estimated that 2–5% of patients with NIDDM may have this form of diabetes mellitus2,3. Clinical studies have shown that predia-betic MODY subjects have normal insulin sensitivity but suffer from a defect in glucose-stimulated insulin secretion, suggesting that pancreatic β-cell dysfunction rather than insulin resistance is the primary defect in this disorder4,5. Linkage studies have localized the genes that are mutated in MODY on human chromosomes 20 (MODY1)6, 7 (MODY2)2 and 12 (MODY3}7, with MODY2 and MODY3 being allelic with the genes encoding glucokinase2, a key regulator of insulin secretion, and hepatocyte nuclear factor-1α (HNF-1α)8, a transcription factor involved in tissue-specific regulation of liver genes but also expressed in pancreatic islets, insulinoma cells and other tissues. Here we show that MODY1 is the gene encoding HNF-4α (gene symbol, TCP14), a member of the steroid/thyroid hormone receptor superfamily and an upstream regulator of HNF-1α expression9–11.

Variants in KCNQ1 are associated with susceptibility to type 2 diabetes mellitus

We carried out a multistage genome-wide association study of type 2 diabetes mellitus in Japanese individuals, with a total of 1,612 cases and 1,424 controls and 100,000 SNPs. The most significant association was obtained with SNPs in KCNQ1, and dense mapping within the gene revealed that rs2237892 in intron 15 showed the lowest P value (6.7 × 10−13, odds ratio (OR) = 1.49). The association of KCNQ1 with type 2 diabetes was replicated in populations of Korean, Chinese and European ancestry as well as in two independent Japanese populations, and meta-analysis with a total of 19,930 individuals (9,569 cases and 10,361 controls) yielded a P value of 1.7 × 10−42 (OR = 1.40; 95% CI = 1.34–1.47) for rs2237892. Among control subjects, the risk allele of this polymorphism was associated with impairment of insulin secretion according to the homeostasis model assessment of β-cell function or the corrected insulin response. Our data thus implicate KCNQ1 as a diabetes susceptibility gene in groups of different ancestries.

A missense mutation in hepatocyte nuclear factor-4 alpha, resulting in a reduced transactivation activity, in human late-onset non-insulin-dependent diabetes mellitus.

Non-insulin-dependent diabetes mellitus (NIDDM) is a heterogeneous disorder characterized by hyperglycemia resulting from defects in insulin secretion and action. Recent studies have found mutations in the hepatocyte nuclear factor-4 alpha gene (HNF-4alpha) in families with maturity-onset diabetes of the young (MODY), an autosomal dominant form of diabetes characterized by early age at onset and a defect in glucose-stimulated insulin secretion. During the course of our search for susceptibility genes contributing to the more common late-onset NIDDM forms, we observed nominal evidence for linkage between NIDDM and markers in the region of the HNF-4alpha/MODY1 locus in a subset of French families with NIDDM diagnosed before 45 yr of age. Thus, we screened these families for mutations in the HNF-4alpha gene. We found a missense mutation, resulting in a valine-to-isoleucine substitution at codon 393 in a single family. This mutation cosegregated with diabetes and impaired insulin secretion, and was not present in 119 control subjects. Expression studies showed that this conservative substitution is associated with a marked reduction of transactivation activity, a result consistent with this mutation contributing to the insulin secretory defect observed in this family.

Cardio-ankle vascular index measures arterial wall stiffness independent of blood pressure

Although brachial-ankle pulse wave velocity (baPWV) is a non-invasive method of detecting arteriosclerosis, it is affected by changes in blood pressure (BP). Cardio-ankle vascular index (CAVI) is a new method for estimating arteriosclerosis, and it has been reported to be less influenced by BP. We investigated the influence of BP changes on CAVI and the correlation of CAVI to clinical factors and carotid arteriosclerosis. CAVI and baPWV in 35 non-diabetic and 33 diabetic subjects were measured in increased BP (after stair climbing) and rested BP (after 10min of rest). Intima-media thickness (IMT) of carotid arteries was measured by ultrasoundsonography. We achieved the following results: CAVI did not show a significant change with a change in BP in both non-diabetic and diabetic subjects. On the contrary, baPWV was significantly influenced by BP changes. Carotid artery IMT had a significant positive correlation with CAVI and baPWV. Multiple regression analysis revealed that significant risk factors of high baPWV were age and systolic BP. On the contrary, significant risk factors of high CAVI were age and hemoglobin A1c, while systolic BP was not relevant. Our findings suggest that CAVI is independent of BP and useful as an indicator of early arteriosclerosis in diabetic subjects.

Islet amyloid polypeptide amide causes peripheral insulin resistance in vivo in dogs

SummaryIslet amyloid polypeptide is a 37 amino acid hormone-like peptide which is the major protein component of islet amyloid deposits commonly found in patients with Type 2 (non-insulin-dependent) diabetes mellitus. Recent studies indicate that a physiologically active form of this peptide appears to be carboxyamidated and secreted from the insulin-producing beta cell. In order to clarify the possible in vivo actions of islet amyloid polypeptide, we have studied the effects of synthesized islet amyloid polypeptide-amide on peripheral glucose utilization by performing hyperinsulinaemic euglycaemic glucose clamp studies on dogs. Exogenously administered islet amyloid polypeptide-amide (an infusion from 1.0 to 100 μg·kg−1·h−1, over 2 h) inhibited the insulin-stimulated glucose disposal rate in a dose dependent manner. Twenty-five μg·kg−1·h−1 of islet amyloid polypeptide-amide infused via a peripheral vein significantly lowered the glucose disposal rate by 20% (from 17.4±1.7 to 14.4±1.7 mg·kg−1·min−1, n = 5, p<0.01). These findings suggest that islet amyloid polypeptide-amide causes peripheral insulin resistance in vivo.

Organization and partial sequence of the hepatocyte nuclear factor-4 alpha/MODY1 gene and identification of a missense mutation, R127W, in a Japanese family with MODY

Hepatocyte nuclear factor-4α (HNF-4α) is a member of the nuclear receptor superfamily, a class of ligand-activated transcription factors. A nonsense mutation in the gene encoding this transcription factor was recently found in a white family with one form of maturity-onset diabetes of the young, MODY1. Here, we report the exonintron organization and partial sequence of the human HNF-4α gene. In addition, we have screened the 12 exons, flanking introns and minimal promoter region for mutations in a group of 57 unrelated Japanese subjects with early-onset NIDDM/MODY of unknown cause. Eight nucleotide substitutions were noted, of which one resulted in the mutation of a conserved arginine residue, Argl27 (CGG)→Trp (TGG) (designated R127W), located in the T-box, a region of the protein that may play a role in HNF-4α dimerization and DNA binding. This mutation was not found in 214 unrelated nondiabetic subjects (53 Japanese, 53 Chinese, 51 white, and 57 African-American). The R127W mutation was only present in three of five diabetic members in this family, indicating that it is not the only cause of diabetes in this family. The remaining seven nucleotide substitutions were located in the proximal promoter region and introns. They are not predicted to affect the transcription of the gene or mRNA processing and represent polymorphisms and rare variants. The results suggest that mutations in the HNF-4α gene may cause early-onset NIDDM/MODY in Japanese but they are less common than mutations in the HNF-1α/MODY3 gene. The information on the sequence of the HNF-4α gene and its promoter region will facilitate the search for mutations in other populations and studies of the role of this gene in determining normal pancreatic β-cell function.

Association of TCF7L2 polymorphisms with susceptibility to type 2 diabetes in 4,087 Japanese subjects

AbstractTranscription factor 7-like 2 (TCF7L2) has been shown to be associated with type 2 diabetes mellitus in multiple ethnic groups. Regarding the Asian population, Horikoshi et al. (Diabetologia 50:747–751, 2007) and Hayashi et al. (Diabetologia 50:980–984, 2007) reported that single nucleotide polymorphisms (SNPs) in TCF7L2 were associated with type 2 diabetes in the Japanese population, while contradictory results were reported for Han Chinese populations. The aim of this study was to investigate the associations of the TCF7L2 gene with type 2 diabetes using a relatively large sample size: 2,214 Japanese individuals with type 2 diabetes and 1,873 normal controls. The minor alleles of rs7903146, rs11196205, and rs12255372 showed significant associations with type 2 diabetes (OR = 1.48, P = 2.7 × 10−4; OR = 1.39, P = 4.6 × 10−4; OR = 1.70, P = 9.8 × 10−5, respectively) in the combined sample sets. However, neither rs11196218 nor rs290487 showed a significant association. These results indicate that TCF7L2 is an important susceptibility gene for type 2 diabetes in the Japanese population.

A mitochondrial DNA variant at position 16189 is associated with type 2 diabetes mellitus in Asians

Aims/hypothesisThis multinational study was conducted to investigate the association between a mitochondrial DNA (mtDNA) T16189C polymorphism and type 2 diabetes in Asians. The mtDNA 16189C variant has been reported to be associated with insulin resistance and type 2 diabetes. However, a recent meta-analysis concluded that it is negatively associated with type 2 diabetes in Europids. Since the phenotype of an mtDNA mutant may be influenced by environmental factors and ethnic differences in the nuclear and mitochondrial genomes, we investigated the association between the 16189C variant and type 2 diabetes in Asians.MethodsThe presence of the mtDNA 16189C variant was determined in 2,469 patients with type 2 diabetes and 1,205 non-diabetic individuals from Korea, Japan, Taiwan, Hong Kong and China. An additional meta-analysis including previously published Asian studies was performed. Since mtDNA nucleotide position 16189 is very close to the mtDNA origin of replication, we performed DNA-linked affinity chromatography and reverse-phase liquid chromatography/tandem mass spectrometry and chromatin immunoprecipitation to identify protein bound to the 16189 region.ResultsAnalysis of participants from five Asian countries confirmed the association between the 16189C variant and type 2 diabetes [odds ratio (OR) 1.256, 95% CI 1.08–1.46, p = 0.003]. Inclusion of data from three previously published Asian studies (type 2 diabetes n = 3,283, controls n = 2,176) in a meta-analysis showed similar results (OR 1.335, 95% CI 1.18–1.51, p = 0.000003). Mitochondrial single-stranded DNA-binding protein (mtSSB) was identified as a candidate protein bound to the 16189 region. Chromatin immunoprecipitation in cybrid cells showed that mtSSB has a lower binding affinity for the 16189C variant than the wild-type sequence.Conclusions/interpretationThe mtDNA 16189C variant is associated with an increased risk of type 2 diabetes in Asians.

Hepatic function in a family with a nonsense mutation (R154X) in the hepatocyte nuclear factor-4alpha/MODY1 gene.

Maturity-onset diabetes of the young (MODY) is a genetically heterogeneous monogenic disorder characterized by autosomal dominant inheritance, onset usually before 25 yr of age, and abnormal pancreatic beta-cell function. Mutations in the hepatocyte nuclear factor(HNF)-4alpha/MODY1, glucokinase/MODY2, and HNF-1alpha/MODY3 genes can cause this form of diabetes. In contrast to the glucokinase and HNF-1alpha genes, mutations in the HNF-4alpha gene are a relatively uncommon cause of MODY, and our understanding of the MODY1 form of diabetes is based on studies of only a single family, the R-W pedigree. Here we report the identification of a second family with MODY1 and the first in which there has been a detailed characterization of hepatic function. The affected members of this family, Dresden-11, have inherited a nonsense mutation, R154X, in the HNF-4alpha gene, and are predicted to have reduced levels of this transcription factor in the tissues in which it is expressed, including pancreatic islets, liver, kidney, and intestine. Subjects with the R154X mutation exhibited a diminished insulin secretory response to oral glucose. HNF-4alpha plays a central role in tissue-specific regulation of gene expression in the liver, including the control of synthesis of proteins involved in cholesterol and lipoprotein metabolism and the coagulation cascade. Subjects with the R154X mutation, however, showed no abnormalities in lipid metabolism or coagulation except for a paradoxical 3.3-fold increase in serum lipoprotein(a) levels, nor was there any evidence of renal dysfunction in these subjects. The results suggest that MODY1 is primarily a disorder of beta-cell function.

Association Studies of Variants in the Genes Involved in Pancreatic β-Cell Function in Type 2 Diabetes in Japanese Subjects

Because impaired insulin secretion is characteristic of type 2 diabetes in Asians, including Japanese, the genes involved in pancreatic β-cell function are candidate susceptibility genes for type 2 diabetes. We examined the association of variants in genes encoding several transcription factors (TCF1, TCF2, HNF4A, ISL1, IPF1, NEUROG3, PAX6, NKX2–2, NKX6–1, and NEUROD1) and genes encoding the ATP-sensitive K+ channel subunits Kir6.2 (KCNJ11) and SUR1 (ABCC8) with type 2 diabetes in a Japanese cohort of 2,834 subjects. The exon 16 −3c/t variant rs1799854 in ABCC8 showed a significant association (P = 0.0073), and variants in several genes showed nominally significant associations (P < 0.05) with type 2 diabetes. Although the E23K variant rs5219 in KCNJ11 showed no association with diabetes in Japanese (for the K allele, odds ratio [OR] 1.08 [95% CI 0.97–1.21], P = 0.15), 95% CI around the OR overlaps in meta-analysis of European populations, suggesting that our results are not inconsistent with the previous studies. This is the largest association study so far conducted on these genes in Japanese and provides valuable information for comparison with other ethnic groups.