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

Molecular Genetics of Type 1 Glycogen Storage Diseases

Glycogen storage disease type 1 (GSD-1), also known as von Gierke disease, is caused by a deficiency in the activity of the enzyme glucose-6-phosphatase (G6Pase). It is an autosomal recessive disorder characterized by hypoglycemia, hepatomegaly, kidney enlargement, growth retardation, lactic acidemia, hyperlipidemia and hyperuricemia. The disease presents with both clinical and biochemical heterogeneity consistent with the existence of two major subgroups, GSD-1a and GSD-1b, which have been confirmed at the molecular genetic level. GSD-1a, the most prevalent form, is caused by mutations in the G6Pase gene that abolish or greatly reduce enzymatic activity. The gene maps to chromosome 17q21 and encodes a microsomal transmembrane protein. Animal models of GSD-1a exist and are being exploited to delineate the disease more precisely. It has been proposed that GSD-1b is caused by a defect in the microsomal glucose-6-phosphate transporter. The gene responsible for GSD-1b has been mapped to chromosome 11q23 and a cDNA encoding a microsomal transmembrane protein has been identified. The function of this putative GSD-1b protein remains to be determined. These recent developments, along with newly characterized animal models of GSD-1a, are increasing our understanding of the interrelationship between the components of the G6Pase complex and type 1 glycogen storage diseases.

Type 2 diabetes: evidence for linkage on chromosome 20 in 716 Finnish affected sib pairs

We are conducting a genome scan at an average resolution of 10 centimorgans (cM) for type 2 diabetes susceptibility genes in 716 affected sib pairs from 477 Finnish families. To date, our best evidence for linkage is on chromosome 20 with potentially separable peaks located on both the long and short arms. The unweighted multipoint maximum logarithm of odds score (MLS) was 3.08 on 20p (location, chi = 19.5 cM) under an additive model, whereas the weighted MLS was 2.06 on 20q (chi = 57 cM, recurrence risk,lambda(s) = 1. 25, P = 0.009). Weighted logarithm of odds scores of 2.00 (chi = 69.5 cM, P = 0.010) and 1.92 (chi = 18.5 cM, P = 0.013) were also observed. Ordered subset analyses based on sibships with extreme mean values of diabetes-related quantitative traits yielded sets of families who contributed disproportionately to the peaks. Two-hour glucose levels in offspring of diabetic individuals gave a MLS of 2. 12 (P = 0.0018) at 9.5 cM. Evidence from this and other studies suggests at least two diabetes-susceptibility genes on chromosome 20. We have also screened the gene for maturity-onset diabetes of the young 1, hepatic nuclear factor 4-a (HNF-4alpha) in 64 affected sibships with evidence for high chromosomal sharing at its location on chromosome 20q. We found no evidence that sequence changes in this gene accounted for the linkage results we observed.

Identification of new mutations in the hepatocyte nuclear factor 4alpha gene among families with early onset Type 2 diabetes mellitus

AIMS

Mutations in hepatocyte nuclear factor (HNF)-4alpha gene located on chromosome 20q have been found to be responsible for the development of early onset Type 2 diabetes mellitus (DM). Through a national campaign, 53 families with autosomal dominant, early onset Type 2 DM (n=654) were assembled to determine the frequency of mutations in the HNF-4alpha gene and their contribution to the development of diabetes.

METHODS

Twelve exons and the promoter region of the HNF-4alpha gene were screened in probands of the families by a double gradient, denaturing gradient gel electrophoresis (DG-DGGE) protocol combined with automated bi-directional sequencing of the PCR products of all heterozygous individuals.

RESULTS

We detected two new mutations in the HNF-4alpha gene that changed the amino-acid sequence. The first mutation was a Gly-->Ser substitution in codon 115 within a highly conserved DNA binding domain, and all six carriers of this mutation had diabetes and low insulin secretion. The second mutation was an Ile-->Val substitution in codon 454 within the transactivation domain. It was carried by four family members, two of whom also carried a mutation in the HNF-1alpha gene. Of those having only the mutation in HNF-4alpha one had diabetes and the other had normal glucose tolerance and both were obese and hyperinsulinaemic. Thus, it is uncertain that this mutation is responsible for any of the diabetes in this family.

CONCLUSION

We have found that mutations in the HNF-4alpha gene account for a small proportion, about 2-4%, of families with early onset, autosomal dominant, Type 2 DM in US Caucasians.

The hepatic nuclear factor-1alpha G319S variant is associated with early-onset type 2 diabetes in Canadian Oji-Cree

Mutations in the gene encoding hepatic nuclear factor-1alpha (HNF-1alpha) have been found in patients with maturity-onset diabetes of the young. We identified a new variant in the HNF-1alpha gene, namely G319S, in Ontario Oji-Cree with type 2 diabetes. G319S is within the proline II-rich domain of the trans-activation site of HNF-1alpha and alters a glycine residue that is conserved throughout evolution. S319 was absent from 990 alleles taken from subjects representing six other ethnic groups, suggesting that it is private for Oji-Cree. We found that 1) the S319 allele was significantly more prevalent in diabetic than nondiabetic Oji-Cree (0.209 vs. 0.087; P = 0.000001); 2) S319/S319 homozygotes and S319/G319 heterozygotes, respectively, had odds ratios for type 2 diabetes of 4.00 (95% confidence interval, 2.65-6.03) and 1.97 (95% confidence interval, 1.44-2.70) compared with G319/G319 homozygotes; 3) there was a significant difference in the mean age of onset of type 2 diabetes, with G319/G319, S319/G319, and S319/S319 subjects affected in the fifth, fourth, and third decades of life, respectively. In subjects with type 2 diabetes, we also found significantly lower body mass index and significantly higher post-challenge plasma glucose in S319/S319 and S319/G319 compared with G319/G319 subjects. Finally, among nondiabetic subjects, S319/G319 heterozygotes had significantly lower plasma insulin than G319/G319 homozygotes. The presence of the private HNF-1alpha G319S variant in a large number of Oji-Cree with type 2 diabetes and its strong association with type 2 diabetes susceptibility are unique among human populations. Also, G319S is associated with a distinct form of type 2 diabetes, characterized by onset at an earlier age, lower body mass, and a higher postchallenge plasma glucose.

Insulin resistance, impaired glucose tolerance and non-insulin-dependent diabetes, pathologic mechanisms and treatment: current status and therapeutic possibilities

Impaired glucose tolerance and non-insulin-dependent diabetes (NIDDM) are the pathologic consequence of two co-incident and interacting conditions, namely insulin resistance and relative insulin deficiency. Recognised by the World Health Authority as a global health problem there are at 1995 estimates at least 110 million diagnosed diabetics world wide with at least the same number undiagnosed. Diabetes is the 4th leading cause of death in developed countries and its management exerts a vast economic and social burden. Insulin resistance is established as the characteristic pathologic feature of patients with glucose intolerance and NIDDM describing a state in which insulin stimulated glucose uptake and utilisation in liver, skeletal muscle and adipose tissue is impaired and coupled to impaired suppression of hepatic glucose output. Although the biochemical mechanisms underpinning both defects are becoming better understood, the genetic and molecular causes remain elusive; and whether insulin resistance or relative insulin deficiency represents the primary defect in patients with NIDDM is the matter of some debate. In this article we review the biochemical and molecular nature of the defects in insulin sensitivity and glucose uptake, and discuss some of the potential causative mechanisms. The genetic and environmental basis of insulin resistance is reviewed and presented, and potential therapeutic targets including thiazolidinediones are discussed.

Autosomally transmitted low concentration of thyroxine-binding globulin

The gene coding for thyroxine-binding globulin (TBG) is located on the long arm of the X chromosome; thus anomalies of TBG are transmitted in an X-linked fashion. We report a family with decreased concentration of circulating TBG and an unusual pattern of inheritance. In this family, a number of members showed decreased levels of serum TBG. The unusual finding was that the low TBG was transmitted from the male proband to his son. Thyroxine (T4) binding affinity and heat lability of serum TBG of the proband was not different from values obtained from a normal control. All exons and the critical region in the upstream of the TBG gene were sequenced and no alterations were found. The mechanism that causes decreased concentration of TBG of the proband and family members is unknown, but an abnormality in transcription factors that are important for TBG gene expression might be considered.

Loci on chromosomes 2 (NIDDM1) and 15 interact to increase susceptibility to diabetes in Mexican Americans

Complex disorders such as diabetes, cardiovascular disease, asthma, hypertension and psychiatric illnesses account for a large and disproportionate share of health care costs, but remain poorly characterized with respect to aetiology. The transmission of such disorders is complex, reflecting the actions and interactions of multiple genetic and environmental factors. Genetic analyses that allow for the simultaneous consideration of susceptibility from multiple regions may improve the ability to map genes for complex disorders, but such analyses are currently computationally intensive and narrowly focused. We describe here an approach to assessing the evidence for statistical interactions between unlinked regions that allows multipoint allele-sharing analysis to take the evidence for linkage at one region into account in assessing the evidence for linkage over the rest of the genome. Using this method, we show that the interaction of genes on chromosomes 2 (NIDDM1) and 15 (near CYP19) makes a contribution to susceptibility to type 2 diabetes in Mexican Americans from Starr County, Texas.

Three-dimensional fibroblast culture implant for the treatment of diabetic foot ulcers: metabolic activity and therapeutic range

Dermagraft is three-dimensional, allogeneic, human neonatal dermal fibroblast culture grown on a degradable scaffold and cryopreserved. Clinical trials for treatment of diabetic foot ulcers showed optimal healing within a therapeutic range of metabolic activity, determined by 3[4,5-dimethylthiazol-2-yl]2,5-diphenyltetrazolium bromide (MTT) reduction. Actions of Dermagraft in wound repair include colonization by cells and provision of growth factors and cytokines, both activities dependent on living cells. Cells in the cryopreserved culture showed 60% viability by dye exclusion and, when isolated, were able to proliferate in monolayer culture. Protein synthesis by Dermagraft was inhibited 70-98% by cryopreservation, but, if within the therapeutic range, recovered to 45-85% of the prefreeze value over 48 h. Subtherapeutic Dermagraft showed variable, low recovery. Expression of mRNA for vascular endothelial growth factor (VEGF), platelet-derived growth factor A chain, and insulin-like growth factor-1 was reduced >83% in subtherapeutic compared with therapeutic Dermagraft. Granulocyte colony-stimulating factor and VEGF protein secretion, determined by enzyme-linked immunosorbent assay (ELISA), and angiogenic activity also depended on therapeutic range. VEGF secretion dropped sharply with MTT reductase in subtherapeutic tissue. The data demonstrate the critical dependence of the therapeutic properties of this living dermal implant on recovery of protein synthesis, growth factor expression, and angiogenesis, determined by metabolic activity.

Ionizing radiation and genetic risks. VI. Chronic multifactorial diseases: a review of epidemiological and genetical aspects of coronary heart disease, essential hypertension and diabetes mellitus

This paper provides a broad overview of the epidemiological and genetical aspects of common multifactorial diseases in man with focus on three well-studied ones, namely, coronary heart disease (CHD), essential hypertension (EHYT) and diabetes mellitus (DM). In contrast to mendelian diseases, for which a mutant gene either in the heterozygous or homozygous condition is generally sufficient to cause disease, for most multifactorial diseases, the concepts of genetic susceptibility' and risk factors' are more appropriate. For these diseases, genetic susceptibility is heterogeneous. The well-studied diseases such as CHD permit one to conceptualize the complex relationships between genotype and phenotype for chronic multifactorial diseases in general, namely that allelic variations in genes, through their products interacting with environmental factors, contribute to the quantitative variability of biological risk factor traits and thus ultimately to disease outcome. Two types of such allelic variations can be distinguished, namely those in genes whose mutant alleles have (i) small to moderate effects on the risk factor trait, are common in the population (polymorphic alleles) and therefore contribute substantially to the variability of biological risk factor traits and (ii) profound effects, are rare in the population and therefore contribute far less to the variability of biological risk factor traits. For all the three diseases considered in this review, a positive family history is a strong risk factor. CHD is one of the major contributors to mortality in most industrialized countries. Evidence from epidemiological studies, clinical correlations, genetic hyperlipidaemias etc., indicate that lipids play a key role in the pathogenesis of CHD. The known lipid-related risk factors include: high levels of low density lipoprotein cholesterol, low levels of high density lipoprotein cholesterol, high apoB levels (the major protein fraction of the low density lipoprotein particles) and elevated levels of Lp(a) lipoprotein. Among the risk factors which are not related to lipids are: high levels of homocysteine, low activity of paraoxonase and possibly also elevated plasma fibrinogen levels. In addition to the above, hypertension, diabetes and obesity (which themselves have genetic determinants) are important risk factors for CHD. Among the environmental risk factors are: high dietary fat intake, smoking, stress, lack of exercise etc. About 60% of the variability of the plasma cholesterol is genetic in origin. While a few genes have been identified whose mutant alleles have large effects on this trait (e.g., LDLR, familial defective apoB-100), variability in cholesterol levels among individuals in most families is influenced by allelic variation in many genes (polymorphisms) as well as environmental exposures. A proportion of this variation can be accounted for by two alleles of the apoE locus that increase (ε4) and decrease (ε2) cholesterol levels, respectively. A polymorphism at the apoB gene (XbaI) also has similar effects, but is probably not mediated through lipids. High density lipoprotein cholesterol levels are genetically influenced and are related to apoA1 and hepatic lipase (LIPC) gene functions. Mutations in the apoA1 gene are rare and there are data which suggest a role of allelic variation at or linked LIPC gene in high density lipoprotein cholesterol levels. Polymorphism at the apoA1--C3 loci is often associated with hypertriglyceridemia. The apo(a) gene which codes for Lp(a) is highly polymorphic, each allele determining a specific number of multiple tandem repeats of a unique coding sequence known as Kringle 4. The size of the gene correlates with the size of the Lp(a) protein. The smaller the size of the Lp(a) protein, the higher are the Lp(a) levels. (ABSTRACT TRUNCATED)

The Ala/Val98 polymorphism of the hepatocyte nuclear factor-1alpha gene contributes to the interindividual variation in serum C-peptide response during an oral glucose tolerance test: evidence from studies of 231 glucose-tolerant first degree relatives of type 2 diabetic probands

The third form of maturity-onset diabetes of the young is caused by mutations in the hepatocyte nuclear factor-1alpha gene. Recently, we demonstrated an association between a prevalent polymorphism at codon 98, Ala/Val98, of this gene and a 20% decreased insulin release during an oral glucose tolerance test (OGTT) in middle-aged glucose-tolerant Danish Caucasian subjects. The major objective of the present study was to replicate this finding among glucose-tolerant first degree relatives of type 2 diabetic patients of the same ethnic origin. All participants, 231 glucose-tolerant offspring of 62 type 2 diabetic probands, underwent an OGTT with measurements of plasma glucose, serum insulin, and serum C peptide during the test. Thirty-three heterozygous carriers of the Ala/Val variant were identified, whereas no subjects had the variant in its homozygous form. Ala/Val carriers had a 20% reduction in serum C peptide at 30 min during the OGTT (1225+/-636 vs. 1507+/-624 pmol/L; P=0.02) compared to wild-type carriers. No significant differences in serum insulin levels during the OGTT were observed between carriers of the variant and Ala/Ala homozygotes. In conclusion, among Danish glucose-tolerant first degree relatives of type 2 diabetic patients the Ala/Val98 polymorphism of the hepatocyte nuclear factor-1alpha gene is associated with a decreased serum C-peptide secretion during an OGTT. This finding confirms our previously reported observation of the functional importance of the variant to insulin secretion during an OGTT among middle-aged healthy subjects.

Medical implications of understanding complex disease traits

The application of genetic mapping to human disease gene identification has led to the definition of many linkages and a few disease genes in complex traits over the past two years. Its application has also increased to include aspects of pharmacogenetics relating to pharmacokinetics and pharmacodynamics.

SRC-1 and GRIP1 coactivate transcription with hepatocyte nuclear factor 4

Hepatocyte nuclear factor-4 (HNF4), a member of the nuclear receptor superfamily, plays an important role in tissue-specific gene expression, including genes involved in hepatic glucose metabolism. In this study, we show that SRC-1 and GRIP1, which act as coactivators for various nuclear receptors, associate with HNF4 in vivo and enhance its transactivation potential. The AF-2 domain of HNF4 is required for this interaction and for the potentiation of transcriptional activity by these coactivators. p300 can also serve as a coactivator with HNF4, and it synergizes with SRC-1 to further augment the activity of HNF4. HNF4 is also a key regulator of the expression of hepatocyte nuclear factor-1 (HNF1). The overexpression of SRC-1 or GRIP1 enhances expression from a HNF1 gene promoter-reporter in HepG2 hepatoma cells, and this requires an intact HNF4-binding site in the HNF1 gene promoter. Type 1 maturity onset diabetes of young (MODY), which is characterized by abnormal glucose-mediated insulin secretion, is caused by mutations of the HNF4 gene. A mutation of the HNF4-binding site in the HNF1 gene promoter has also been associated with MODY. Thus, HNF4 is involved in the regulation of glucose homeostasis at several levels and along with the SRC-1, GRIP1, and p300 may play an important role in the pathophysiology of non-insulin-dependent diabetes mellitus.

Dominant-negative suppression of HNF-1alpha function results in defective insulin gene transcription and impaired metabolism-secretion coupling in a pancreatic beta-cell line

Mutations in the hepatocyte nuclear factor-1alpha (HNF-1alpha) have been linked to subtype 3 of maturity-onset diabetes of the young (MODY3), which is characterized by a primary defect in insulin secretion. The role of HNF-1alpha in the regulation of pancreatic beta-cell function was investigated. Gene manipulation allowed graded overexpression of HNF-1alpha and controlled dominant-negative suppression of HNF-1alpha function in insulinoma INS-1 cells. We show that HNF-1alpha is essential for insulin gene transcription, as demonstrated by a pronounced decrease in insulin mRNA expression and in insulin promoter activity under dominant-negative conditions. The expression of genes involved in glucose transport and metabolism including glucose transporter-2 and L-type pyruvate kinase is also regulated by HNF-1alpha. Loss of HNF-1alpha function leads to severe defects in insulin secretory responses to glucose and leucine, resulting from impaired glucose utilization and mitochondrial oxidation. The nutrient-evoked ATP production and subsequent changes in plasma membrane potential and intracellular Ca2+ were diminished by suppression of HNF-1alpha function. These results suggest that HNF-1alpha function is essential for maintaining insulin storage and nutrient-evoked release. The defective mitochondrial oxidation of metabolic substrates causes impaired insulin secretion, indicating a molecular basis for the diabetic phenotype of MODY3 patients.

The effect of two frequent amino acid variants of the hepatocyte nuclear factor-1alpha gene on estimates of the pancreatic beta-cell function in Caucasian glucose-tolerant first-degree relatives of type 2 diabetic patients

The objective of the present study was to investigate whether the frequent amino acid polymorphisms, Ile/Leu27 and Ser/Asn487, of the hepatocyte nuclear factor-1alpha gene were associated with alterations in glucose-induced serum C-peptide and serum insulin responses among glucose-tolerant first-degree relatives of type 2 diabetic patients. The study comprised 2 independent Danish cohorts. Among 74 unrelated type 2 diabetic relatives, 12 homozygous carriers of the Ile/Leu27 polymorphism had a 32% decrease in the 30-min serum C-peptide level (P = 0.01), as well as a 39% decrease in the 30-min serum insulin level (P = 0.02) during an oral glucose tolerance test. Ten homozygous carriers of the Ile/Leu27 variant did, however, not differ from wild-type carriers, with respect to the acute circulating insulin and serum C-peptide responses during an i.v. glucose tolerance test in the same study cohort. In a larger (more than 3-fold) study group of 230 glucose tolerant offspring of 62 type 2 diabetic probands, 33 homozygous carriers of the Ile/Leu27 variant did not differ, with respect to either serum insulin and serum C-peptide levels during an oral glucose tolerance test or acute serum insulin and serum C-peptide responses during an i.v. glucose tolerance test. We therefore consider the former positive finding as a statistical type I error. There were no differences in the above mentioned variables between carriers of the Ser/Asn487 polymorphism and wild-type carriers within any of the 2 study populations. Nor did carriers of combined genotypes, i.e. carriers of both the Ile/Leu27 and the Ser/Asn487 variants, show any associations with the examined variables. In conclusion, the Ile/Leu27 and Ser/ Asn487 polymorphisms of the hepatocyte nuclear factor-1alpha gene have apparently no major impact on the pancreatic beta-cell function, after an oral and i.v. glucose challenge, in Caucasian first-degree relatives of type 2 diabetic patients.

The genetic basis of diabetes mellitus

Familial risk, pathogenesis, clinical onset, and treatment of diabetes mellitus vary according to etiology. Although Type 2 diabetes has a higher familial risk, more is known about the genetics of Type 1 diabetes. Genes contributing 60% to 65% of susceptibility to Type 1 diabetes mellitus are known. Type 1 diabetes is associated with susceptibility genes in the HLA region on chromosome 6p21 and the insulin gene on chromosome 11p15, and at least eight additional susceptibility genes are under investigation. Islet cytoplasmic antibodies provide humoral evidence of Type 1 diabetes risk. Only 10% of the genes contributing susceptibility to Type 2 diabetes mellitus are known, and they are primarily associated with uncommon subtypes of the disorder. The insulin receptor gene on chromosome 19p13 and at least five glucose transporter genes contribute to Type 2 diabetes susceptibility, and further associations may emerge from study of the glycogen synthase gene, the glucokinase gene, the MODY genes, and the leptin gene. Diabetes comorbidities may result from genetic and environmental susceptibilities independently or in combination.

RNA splicing of bacterial genes in eukaryotes

The presence of intervening sequences or introns in eukaryotic genes has been known for more than 20 years, and the mechanisms underlying RNA splicing have been studied in depth both genetically and biochemically. In recent years, however, an increasing number of bacterial genes have been introduced into higher eukaryotes as important tools for genetic studies. Their gene products are frequently used as an indirect measure for cell type-specific promoter activity, as, for example, in the case of chloramphenicol acetyl transferase (CAT assay) or beta-galactosidase. Here we show that RNA splicing of two prokaryotic genes encoding site-specific DNA recombinases occurs in eukaryotic cells. In one case, splicing is only observed after treatment of cells with the cytokine alpha interferon. We further demonstrate that mutating an intragenic donor splice site in a bacterial gene apparently activates a second, alternative splicing pathway. In conjunction with previous reports, our findings should also be regarded as a warning that splicing of bacterial genes in higher eukaryotes is a more common phenomenon than presently recognized, which may be difficult to overcome and may cause problems in the interpretation of experimental results.

Evidence for oligogenic inheritance of type 1 diabetes in a large Bedouin Arab family

Based on a genomic search for linkage, a locus contributing to type 1 diabetes in a large Bedouin Arab family (19 affected relatives) maps to the long arm of chromosome 10 (10q25; nonparametric linkage = 4.99; P = 0.00004). All affected relatives carry one or two high-risk HLA-DR3 haplotypes that are rarely found in other family members. One chromosome 10 haplotype, the B haplotype, was transmitted from a heterozygous parent to 13 of 13 affected offspring compared to 10 of 23 unaffected siblings. Recombination events occurring on this haplotype place the susceptibility locus in an 8-cM interval between markers D10S1750 and D10S1773. Two adjacent markers, D10S592 and D10S554, showed evidence of linkage disequilibrium with the disease locus. A 273-bp allele at D10S592 was transmitted to 8 of 10 affected offspring compared to 3 of 14 unaffected siblings, and a 151-bp allele at D10S554 was transmitted to 15 of 15 affected offspring compared with 10 of 24 unaffected siblings. D10S554 and D10S592 and the closest flanking markers are contained in a 1,240-kb yeast artificial chromosome, a region small enough to proceed with positional cloning.

An autosomal genomic scan for loci linked to type II diabetes mellitus and body-mass index in Pima Indians

Genetic factors influence the development of type II diabetes mellitus, but genetic loci for the most common forms of diabetes have not been identified. A genomic scan was conducted to identify loci linked to diabetes and body-mass index (BMI) in Pima Indians, a Native American population with a high prevalence of type II diabetes. Among 264 nuclear families containing 966 siblings, 516 autosomal markers with a median distance between adjacent markers of 6.4 cM were genotyped. Variance-components methods were used to test for linkage with an age-adjusted diabetes score and with BMI. In multipoint analyses, the strongest evidence for linkage with age-adjusted diabetes (LOD = 1.7) was on chromosome 11q, in the region that was also linked most strongly with BMI (LOD = 3.6). Bivariate linkage analyses strongly rejected both the null hypothesis of no linkage with either trait and the null hypothesis of no contribution of the locus to the covariation among the two traits. Sib-pair analyses suggest additional potential diabetes-susceptibility loci on chromosomes 1q and 7q.

Defective pancreatic beta-cell glycolytic signaling in hepatocyte nuclear factor-1alpha-deficient mice

Mutations in the hepatocyte nuclear factor-1alpha (HNF-1alpha) gene cause maturity onset diabetes of the young type 3, a form of type 2 diabetes mellitus. In mice lacking the HNF-1alpha gene, insulin secretion and intracellular calcium ([Ca2+]i) responses were impaired following stimulation with nutrient secretagogues such as glucose and glyceraldehyde but normal with non-nutrient stimuli such as potassium chloride. Patch clamp recordings revealed ATP-sensitive K+ currents (KATP) in beta-cells that were insensitive to suppression by glucose but normally sensitive to ATP. Exposure to mitochondrial substrates suppressed KATP, elevated [Ca2+]i, and corrected the insulin secretion defect. NAD(P)H responses to glucose were substantially reduced, and inhibitors of glycolytic NADH generation reproduced the mutant phenotype in normal islets. Flux of glucose through glycolysis in islets from mutant mice was reduced, as a result of which ATP generation in response to glucose was impaired. We conclude that hepatocyte nuclear factor-1alpha diabetes results from defective beta-cell glycolytic signaling, which is potentially correctable using substrates that bypass the defect.

p59OASL, a 2'-5' oligoadenylate synthetase like protein: a novel human gene related to the 2'-5' oligoadenylate synthetase family

The 2'-5' oligoadenylate synthetases form a well conserved family of interferon induced proteins, presumably present throughout the mammalian class. Using the Expressed Sequence Tag databases, we have identified a novel member of this family. This protein, which we named p59 2'-5' oligoadenylate synthetase-like protein (p59OASL), shares a highly conserved N-terminal domain with the known forms of 2'-5' oligoadenylate synthetases, but differs completely in its C-terminal part. The C-terminus of p59OASL is formed of two domains of ubiquitin-like sequences. Here we present the characterisation of a full-length cDNA clone, the genomic sequence and the expression pattern of this gene. We have addressed the evolution of the 2'-5' oligoadenylate synthetase gene family, in the light of both this new member and new 2'-5' oligoadenylate synthetase sequence data from other species, which have recently appeared in the databases.

In situ hybridization with 33P-labeled RNA probes for determination of cellular expression patterns of liver transcription factors in mouse embryos

Murine hepatocyte nuclear factor-3beta (HNF-3beta) protein is a member of a large family of developmentally regulated transcription factors that share homology in the winged helix/fork head DNA binding domain and that participate in embryonic pattern formation. HNF-3beta also mediates cell-specific transcription of genes important for the function of hepatocytes, intestinal and bronchiolar epithelium, and pancreatic acinar cells. We have previously identified a hepatocyte and pancreatic cut-homeodomain transcription factor, HNF-6, which is required for HNF-3beta promoter activity. In this study, we used in situ hybridization studies of stage-specific embryos to demonstrate that HNF-6 and its target gene, HNF-3beta, are coexpressed in the foregut endoderm and in the pancreatic and hepatic diverticulum. More detailed analysis of HNF-6 and HNF-3beta's developmental expression patterns provides evidence of colocalization in hepatocytes, intestinal epithelium, and pancreatic ductal epithelium and exocrine acinar cells. In support of the role of HNF-6 in regulating HNF-3beta expression in developing hepatocytes, their liver expression levels are both transiently reduced between 14 and 15 days of gestation. At day 18 of gestation and in adult pancreas, HNF-6 and HNF-3beta transcripts remain colocalized in the exocrine acinar cells, but their expression patterns diverge in endocrine cells. HNF-3beta expression is restricted to the endocrine cells of the islets of Langerhans, whereas the ductal epithelium expresses HNF-6. We discuss these expression patterns with respect to specification of hepatocytes and differentiation of the endocrine and exocrine pancreas.

Hepatocyte nuclear factor-1 acts as an accessory factor to enhance the inhibitory action of insulin on mouse glucose-6-phosphatase gene transcription

Glucose-6-phosphatase catalyzes the terminal step in the gluconeogenic and glycogenolytic pathways. Transcription of the gene encoding the glucose-6-phosphatase catalytic subunit (G6Pase) is stimulated by cAMP and glucocorticoids whereas insulin strongly inhibits both this induction and basal G6Pase gene transcription. Previously, we have demonstrated that the maximum repression of basal G6Pase gene transcription by insulin requires two distinct promoter regions, designated A (from -271 to -199) and B (from -198 to -159). Region B contains an insulin response sequence because it can confer an inhibitory effect of insulin on the expression of a heterologous fusion gene. By contrast, region A fails to mediate an insulin response in a heterologous context, and the mutation of region B within an otherwise intact promoter almost completely abolishes the effect of insulin on basal G6Pase gene transcription. Therefore, region A is acting as an accessory element to enhance the effect of insulin, mediated through region B, on G6Pase gene transcription. Such an arrangement is a common feature of cAMP and glucocorticoid-regulated genes but has not been previously described for insulin. A combination of fusion gene and protein-binding analyses revealed that the accessory factor binding region A is hepatocyte nuclear factor-1. Thus, despite the usually antagonistic effects of cAMP/glucocorticoids and insulin, all three agents are able to use the same factor to enhance their action on gene transcription. The potential role of G6Pase overexpression in the pathophysiology of MODY3 and 5, rare forms of diabetes caused by hepatocyte nuclear factor-1 mutations, is discussed.

Molecular screening of uncoupling protein 2 gene in patients with noninsulin-dependent diabetes mellitus or obesity

Uncoupling protein 2 (UCP2), a member of the family of mitochondrial carrier proteins, has been implicated in the control of whole-body energy balance. The coding region of the human UCP2 gene has now been shown to comprise six exons, and the sequences of the exon-intron boundaries were determined. With the use of this sequence information, 25 Japanese patients with obesity and noninsulin-dependent diabetes mellitus (NIDDM) and 25 subjects with simple obesity were screened for mutations in the entire coding region of UCP2 by PCR and single-strand conformation polymorphism analysis. Two nucleotide polymorphisms resulting in Ala55 --> Val and Ala232 --> Thr substitutions were detected. With the use of PCR and restriction fragment length polymorphism analysis, the allele frequencies for each of these polymorphisms were determined in 210 Japanese patients with NIDDM, 42 obese individuals, and 218 normal control subjects. The frequency of the Val55 allele did not differ significantly among the NIDDM group (46.0%), the obesity group (48.8%), and the normal control group (48.4%). The Thr232 allele was detected in only three subjects, who were heterozygotes and in the NIDDM group (allele frequency, 0.7%). However, expression in yeast of the human wild-type UCP2 protein and UCP2 containing Thr232 revealed no difference in functional activity. These results indicate that the Ala55 --> Val and Ala232 --> Thr variants of UCP2 do not play an important role in the pathogenesis of NIDDM or obesity in the Japanese population.

Autoantibodies against CD38 (ADP-ribosyl cyclase/cyclic ADP-ribose hydrolase) that impair glucose-induced insulin secretion in noninsulin- dependent diabetes patients

Cyclic ADP-ribose (cADPR) has been shown to be a mediator for intracellular Ca2+ mobilization for insulin secretion by glucose in pancreatic beta cells, and CD38 shows both ADP-ribosyl cyclase to synthesize cADPR from NAD+ and cADPR hydrolase to hydrolyze cADPR to ADP-ribose. We show here that 13.8% of Japanese non-insulin-dependent diabetes (NIDDM) patients examined have autoantibodies against CD38 and that the sera containing anti-CD38 autoantibodies inhibit the ADP-ribosyl cyclase activity of CD38 (P </= 0.05). Insulin secretion from pancreatic islets by glucose is significantly inhibited by the addition of the NIDDM sera with anti-CD38 antibodies (P </= 0.04-0.0001), and the inhibition of insulin secretion is abolished by the addition of recombinant CD38 (P </= 0.02). The increase of cADPR levels in pancreatic islets by glucose was also inhibited by the addition of the sera (P </= 0.05). These results strongly suggest that the presence of anti-CD38 autoantibodies in NIDDM patients can be one of the major causes of impaired glucose-induced insulin secretion in NIDDM.

Insulin promoter factor-1 gene mutation linked to early-onset type 2 diabetes mellitus directs expression of a dominant negative isoprotein

The homeodomain transcription factor insulin promoter factor-1 (IPF-1) is required for development of the pancreas and also mediates glucose-responsive stimulation of insulin gene transcription. Earlier we described a human subject with pancreatic agenesis attributable to homozygosity for a cytosine deletion in codon 63 of the IPF-1 gene (Pro63fsdelC). Pro63fsdelC resulted in the premature truncation of an IPF-1 protein which lacked the homeodomain required for DNA binding and nuclear localization. Subsequently, we linked the heterozygous state of this mutation with type 2 diabetes mellitus in the extended family of the pancreatic agenesis proband. In the course of expressing the mutant IPF-1 protein in eukaryotic cells, we detected a second IPF-1 isoform, recognized by COOH- but not NH2-terminal-specific antisera. This isoform localizes to the nucleus and retains DNA-binding functions. We provide evidence that internal translation initiating at an out-of-frame AUG accounts for the appearance of this protein. The reading frame crosses over to the wild-type IPF-1 reading frame at the site of the point deletion just carboxy proximal to the transactivation domain. Thus, the single mutated allele results in the translation of two IPF-1 isoproteins, one of which consists of the NH2-terminal transactivation domain and is sequestered in the cytoplasm and the second of which contains the COOH-terminal DNA-binding domain, but lacks the transactivation domain. Further, the COOH-terminal mutant IPF-1 isoform does not activate transcription and inhibits the transactivation functions of wild-type IPF-1. This circumstance suggests that the mechanism of diabetes in these individuals may be due not only to reduced gene dosage, but also to a dominant negative inhibition of transcription of the insulin gene and other beta cell-specific genes regulated by the mutant IPF-1.

Issues and strategies in the genetic analysis of alcoholism and related addictive behaviors

Research into the genetics of alcoholism susceptibility and related behaviors has become highly contentious for a number of reasons: at issue is the identification of factors that may ultimately determine human behaviors, the limitations of the technologies being used to conduct relevant studies have not been assessed exhaustively, and independent studies have produced widely different results. Addressing these and other questions of relevance in the dissection of the genetic basis of alcoholism susceptibility will be nothing if not difficult. In this article, we consider issues related to one not-so-minor research angle being used more and more in investigations of alcoholism and related disorders: the identification of susceptibility loci through the use of anonymous (or seemingly anonymous) DNA markers. We also consider issues that might promote (or resist) the reconcilability of independent study results, and describe some basic strategies that might help make study results more compelling in light of the complexity of alcoholism and related behaviors.

Maturity-onset diabetes of the young: recent findings indicate insulin resistance/obesity are not factors

Maturity-onset diabetes of the young (MODY) is a relatively rare subtype of type 2 diabetes characterized by an early age of onset and autosomal dominant inheritance. Unlike type 2 diabetes, which is often associated with insulin resistance, MODY is caused by a primary defect in pancreatic beta-cell function resulting in a decrease in insulin secretion. Obesity is not a feature of MODY. However, environmental stressors that increase the demand for insulin, such as illness or puberty, may unmask the genetically limited insulin secretory reserve of the undiagnosed MODY patient. Euglycemia is the primary goal of therapy, and diet is the cornerstone of glycemic control. Sulfonylureas and/or exogenous insulin may also be required depending on the degree of dysfunction of the beta cells.

Mice lacking the homeodomain transcription factor Nkx2.2 have diabetes due to arrested differentiation of pancreatic beta cells

The endocrine pancreas is organized into clusters of cells called islets of Langerhans comprising four well-defined cell types: alpha beta, delta and PP cells. While recent genetic studies indicate that islet development depends on the function of an integrated network of transcription factors, the specific roles of these factors in early cell-type specification and differentiation remain elusive. Nkx2.2 is a member of the mammalian NK2 homeobox transcription factor family that is expressed in the ventral CNS and the pancreas. Within the pancreas, we demonstrate that Nkx2.2 is expressed in alpha, beta and PP cells, but not in delta cells. In addition, we show that mice homozygous for a null mutation of Nkx2.2 develop severe hyperglycemia and die shortly after birth. Immunohistochemical analysis reveals that the mutant embryos lack insulin-producing beta cells and have fewer glucagon-producing alpha cells and PP cells. Remarkably, in the mutants there remains a large population of islet cells that do not produce any of the four endocrine hormones. These cells express some beta cell markers, such as islet amyloid polypeptide and Pdx1, but lack other definitive beta cell markers including glucose transporter 2 and Nkx6.1. We propose that Nkx2.2 is required for the final differentiation of pancreatic beta cells, and in its absence, beta cells are trapped in an incompletely differentiated state.

Genetic testing for maturity onset diabetes of the young in childhood hyperglycaemia

Mild hyperglycaemia is a common finding during minor illness in children. The differential diagnosis includes maturity onset diabetes of the young (MODY), which can be a difficult diagnosis to make clinically. As most genes resulting in MODY have been identified, it is possible to make a firm diagnosis using mutation detection. A case is reported of a 4 year old girl in whom a diagnosis of MODY2 was established by the finding of a heterozygous missense mutation in exon 7 of the glucokinase gene, resulting in the substitution at codon 259 of alanine by threonine (A259T). Observations from other glucokinase families suggest that hyperglycaemia in this child is likely to be stable and will not require intensive medical follow up, whereas other forms of MODY (1, 3, and 4) might carry a different prognosis.

Glucocorticoid exposure in late gestation permanently programs rat hepatic phosphoenolpyruvate carboxykinase and glucocorticoid receptor expression and causes glucose intolerance in adult offspring

Low birth weight in humans is predictive of insulin resistance and diabetes in adult life. The molecular mechanisms underlying this link are unknown but fetal exposure to excess glucocorticoids has been implicated. The fetus is normally protected from the higher maternal levels of glucocorticoids by feto-placental 11beta-hydroxysteroid dehydrogenase type-2 (11beta-HSD2) which inactivates glucocorticoids. We have shown previously that inhibiting 11beta-HSD2 throughout pregnancy in rats reduces birth weight and causes hyperglycemia in the adult offspring. We now show that dexamethasone (a poor substrate for 11beta-HSD2) administered to pregnant rats selectively in the last week of pregnancy reduces birth weight by 10% (P < 0.05), and produces adult fasting hyperglycemia (treated 5.3+/-0.3; control 4.3+/-0.2 mmol/ liter, P = 0.04), reactive hyperglycemia (treated 8.7+/-0.4; control 7.5+/-0.2 mmol/liter, P = 0.03), and hyperinsulinemia (treated 6.1+/-0.4; control 3.8+/-0.5 ng/ml, P = 0.01) on oral glucose loading. In the adult offspring of rats exposed to dexamethasone in late pregnancy, hepatic expression of glucocorticoid receptor (GR) mRNA and phosphoenolpyruvate carboxykinase (PEPCK) mRNA (and activity) are increased by 25% (P = 0.01) and 60% (P < 0.01), respectively, while other liver enzymes (glucose-6-phosphatase, glucokinase, and 11beta-hydroxysteroid dehydrogenase type-1) are unaltered. In contrast dexamethasone, when given in the first or second week of gestation, has no effect on offspring insulin/glucose responses or hepatic PEPCK and GR expression. The increased hepatic GR expression may be crucial, since rats exposed to dexamethasone in utero showed potentiated glucose responses to exogenous corticosterone. These observations suggest that excessive glucocorticoid exposure late in pregnancy predisposes the offspring to glucose intolerance in adulthood. Programmed hepatic PEPCK overexpression, perhaps mediated by increased GR, may promote this process by increasing gluconeogenesis.

Defective insulin secretion in hepatocyte nuclear factor 1alpha-deficient mice

Mutations in the gene for the transcription factor hepatocyte nuclear factor (HNF) 1alpha cause maturity-onset diabetes of the young (MODY) 3, a form of diabetes that results from defects in insulin secretion. Since the nature of these defects has not been defined, we compared insulin secretory function in heterozygous [HNF-1alpha (+/-)] or homozygous [HNF-1alpha (-/-)] mice with null mutations in the HNF-1alpha gene with their wild-type littermates [HNF-1alpha (+/+)]. Blood glucose concentrations were similar in HNF-1alpha (+/+) and (+/-) mice (7.8+/-0.2 and 7.9+/-0.3 mM), but were significantly higher in the HNF-1alpha (-/-) mice (13.1+/-0.7 mM, P < 0.001). Insulin secretory responses to glucose and arginine in the perfused pancreas and perifused islets from HNF-1alpha (-/-) mice were < 15% of the values in the other two groups and were associated with similar reductions in intracellular Ca2+ responses. These defects were not due to a decrease in glucokinase or insulin gene transcription. beta cell mass adjusted for body weight was not reduced in the (-/-) animals, although pancreatic insulin content adjusted for pancreas weight was slightly lower (0.06+/-0.01 vs. 0.10+/-0.01 microg/mg, P < 0.01) than in the (+/+) animals. In summary, a null mutation in the HNF-1alpha gene in homozygous mice leads to diabetes due to alterations in the pathways that regulate beta cell responses to secretagogues including glucose and arginine. These results provide further evidence in support of a key role for HNF-1alpha in the maintenance of normal beta cell function.

Mapping of murine diabetogenic gene mody on chromosome 7 at D7Mit258 and its involvement in pancreatic islet and beta cell development during the perinatal period

Mutation of the murine maturity-onset diabetes mellitus of the young (Mody) locus induces diabetes, but the effects of its homozygosity on the pancreas remain unknown. F2 mice were obtained by F1 (diabetic C57BL6 x normal Mus musculus castaneus) crosses. About 20% of the F2 progeny developed diabetes by 2 wk of age, 50% of the progeny were normal at 2 wk and developed diabetes between 5 and 8 wk of age, and the remaining 30% did not develop diabetes. Quantitative trait locus analysis using blood glucose levels of 118 F2 mice at 2 wk of age and 5-8 wk of age located Mody within 3 cM of D7Mit258. Histopathological investigation revealed hypoplastic islets (approximately 33% of that of wild-type mice) and a lower density of beta cells (approximately 20% of wild-type) with a reciprocal dominance of alpha cells (four times that of wild-type) in Mody homozygotes. Electron microscopic observations revealed a specific decrease in the number of insulin secretory granules and a lower density of beta cells. Ratios of insulin to glucagon contents confirmed specific decreases in insulin content: 0.01 for homozygotes, 0.54 for heterozygotes, and 1.11 for wild-type mice on day 14. These results suggest that Mody is involved in both islet growth and beta cell function.

Gene-environment interactions in the pathogenesis of type 2 diabetes mellitus: lessons learned from the Pima Indians

The comprehensive longitudinal studies of diabetes conducted in the Pima Indians of Arizona over the last 30 years indicate that both genetic and environmental factors play a critical role in the pathogenesis of the disease. Pre- and postnatal exposures as well as diet and physical activity in adulthood markedly affect risk of developing NIDDM in this population. In addition, the high prevalence of diabetes in the Pimas relative to other populations and the familiality of the disease and its precursors, strongly suggest a substantial genetic basis. Interactions between genes and the environment are obviously important in the pathogenesis of NIDDM, but it remains unclear exactly how these interactions occur and how to adequately account for these effects when searching for genes contributing to diabetes. The realization that gene-environment interactions are significant, and may be the dominant mechanism increasing susceptibility to NIDDM, should encourage further investigations. Future progress in studying the genetics of NIDDM and other complex diseases will come not only from technical advances currently in development, but also from advances in understanding the pathophysiology of the disease and the role of gene-environment interactions, and a renewed emphasis on careful clinical characterization of subjects participating in these studies.

Laron dwarfism and non-insulin-dependent diabetes mellitus in the Hnf-1alpha knockout mouse

Mice deficient in hepatocyte nuclear factor 1 alpha (HNF-1alpha) were produced by use of the Cre-loxP recombination system. HNF-1alpha-null mice are viable but sterile and exhibit a phenotype reminiscent of both Laron-type dwarfism and non-insulin-dependent diabetes mellitus (NIDDM). In contrast to an earlier HNF-1alpha-null mouse line that had been produced by use of standard gene disruption methodology (M. Pontoglio, J. Barra, M. Hadchouel, A. Doyen, C. Kress, J. P. Bach, C. Babinet, and M. Yaniv, Cell 84:575-585, 1996), these mice exhibited no increased mortality and only minimal renal dysfunction during the first 6 months of development. Both dwarfism and NIDDM are most likely due to the loss of expression of insulin-like growth factor I (IGF-I) and lower levels of insulin, resulting in stunted growth and elevated serum glucose levels, respectively. These results confirm the functional significance of the HNF-1alpha regulatory elements that had previously been shown to reside in the promoter regions of both the IGF-I and the insulin genes.

Surfactant proteins: molecular genetics of neonatal pulmonary diseases

Genetic and phenotypic complexity has been described for diseases of varied etiology. Groups of patients with varied phenotype can be used in association studies as an initial approach to identify contributing loci. Although association studies have limitations, their value is enhanced by using candidate genes with functions related to disease. Surfactant proteins have been studied in the etiopathogenesis of neonatal pulmonary diseases. SP-A and SP-B polymorphisms are found at a higher frequency in certain groups of patients with respiratory distress syndrome (RDS), and SP-B mutations are linked to the pathogenesis of congenital alveolar proteinosis (CAP). Phenotypic heterogeneity is observed for both CAP and RDS. The available data suggest that a number of factors contribute to the etiology of CAP and RDS and, therefore, a multidisciplinary approach of clinical, genetic, epidemiologic, and statistical considerations is necessary for an in-depth understanding of the pathophysiology of these and other pulmonary diseases.

Circadian periodicity of intestinal Na+/glucose cotransporter 1 mRNA levels is transcriptionally regulated

Intestinal expression of the high affinity Na+/glucose cotransporter 1 (SGLT1), which absorbs dietary glucose and galactose, exhibits both circadian periodicity in its activity and induction by dietary carbohydrate. Because the daily variation in SGLT1 activity is established by the feeding schedule (whether ad libitum or imposed) and persists in the absence of food, this variation has been described as anticipatory. To delineate the mechanisms regulating SGLT1, its expression was examined in rats maintained in a 12-h photoperiod with free access to chow. SGLT1 mRNA levels varied significantly, with the maximum abundance occurring near the onset of dark and the minimum near the onset of light. The SGLT1 transcription rate was 7-fold higher in the morning (1000-1100 h) than in the afternoon (1600-1700 h). An element for hepatocyte nuclear factor 1 (HNF-1) was identified in the SGLT1 promoter that formed different complexes with small intestinal nuclear extracts, depending on the time when the source animal was killed. Serological tests indicated that HNF-1alpha was present in complexes throughout the day, while HNF-1beta binding exhibited circadian periodicity. We propose that exchange of HNF-1 dimerization partners contributes to circadian changes in SGLT1 transcription. Because SGLT1 mRNA levels also varied in rhesus monkeys (offset by approximately one-half day from rats), a similar mechanism appears to be present in primates.

An autosomal genomic scan for loci linked to prediabetic phenotypes in Pima Indians

Type 2 diabetes mellitus is a common chronic disease that is thought to have a substantial genetic basis. Identification of the genes responsible has been hampered by the complex nature of the syndrome. Abnormalities in insulin secretion and insulin action predict the development of type 2 diabetes and are, themselves, highly heritable traits. Since fewer genes may contribute to these precursors of type 2 diabetes than to the overall syndrome, such genes may be easier to identify. We, therefore, undertook an autosomal genomic scan to identify loci linked to prediabetic traits in Pima Indians, a population with a high prevalence of type 2 diabetes. 363 nondiabetic Pima Indians were genotyped at 516 polymorphic microsatellite markers on all 22 autosomes. Linkage analyses were performed using three methods (single-marker, nonparametric multipoint [MAPMAKER/SIBS], and variance components multipoint). These analyses provided evidence for linkage at several chromosomal regions, including 3q21-24 linked to fasting plasma insulin concentration and in vivo insulin action, 4p15-q12 linked to fasting plasma insulin concentration, 9q21 linked to 2-h insulin concentration during oral glucose tolerance testing, and 22q12-13 linked to fasting plasma glucose concentration. These results suggest loci that may harbor genes contributing to type 2 diabetes in Pima Indians. None of the linkages exceeded a LOD score of 3.6 (a 5% probability of occurring in a genome-wide scan). These findings must, therefore, be considered tentative until extended in this population or replicated in others.

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.

Non-insulin dependent diabetes mellitus (NIDDM) in minority youth: research priorities and needs

The prevalence of non-insulin dependent diabetes mellitus (NIDDM) is increasing in Native American and African-American youth, with females more frequently affected than males. This increase is related to increasing rates of obesity and to the greater demand for insulin at adolescence. This review examines the epidemiologic data about NIDDM in minority youth and addresses questions about the type of diabetes minority youth have, the relative contributions of environment and genetics to their diabetes, and whether prevention or control is possible. The heterogeneity of NIDDM in the minority youth population includes: typical NIDDM; atypical diabetes mellitus (ADM), which has been described in a substantial number of African-American youngsters; and a small proportion with a range of defects in the pathway of insulin action. Clinical and experimental evidence that insulin resistance or insulin deficiency is the primary defect in NIDDM are reviewed, as is evidence that fetal undernutrition may be a contributing factor. The numerous reports of linkages, associations, and mutations or polymorphisms in candidate genes account for a very small proportion of non-type 1 diabetes. Environmental and genetic contributors to obesity are also important. Research issues relating to the questions discussed include the need for data comparing various populations and assessing risk factors associated with the epidemic of NIDDM and obesity, costs to the health system and attendant personal and societal costs, clarification of the types of NIDDM in minority populations that will permit appropriate therapy and counseling, and extensive studies of environmental and genetic factors. Genetic studies include a genome wide search and continued analysis for candidate genes for both NIDDM and obesity. Environmental factors for study include the role of fetal and perinatal nutrition and drug exposure. Finally, collaborative multicenter studies are needed of prevention or control of obesity and NIDDM.

Defects in insulin secretion and insulin action in non-insulin-dependent diabetes mellitus are inherited. Metabolic studies on offspring of diabetic probands

No studies are available that have compared early defects in glucose metabolism in the offspring of insulin-deficient and insulin-resistant probands with non-insulin-dependent diabetes mellitus (NIDDM). To investigate this issue, we evaluated insulin secretion capacity with oral and intravenous glucose tolerance tests and with the hyperglycemic clamp, and insulin action with the euglycemic insulin clamp in 20 offspring of NIDDM patients with low fasting C-peptide (+/-450 pmol/liter), reflecting deficient insulin secretion (IS-group), 18 offspring of NIDDM patients with high fasting C-peptide (>/= 880 pmol/liter), reflecting insulin resistance (IR-group), and 14 healthy control subjects without a family history of NIDDM. The frequency of impaired glucose tolerance was 45.0% in the IS-group and 50% in the IR-group. The IS-group had lower insulin-glucose response at 30 min in the oral glucose tolerance test (85.2+/-10.0 pmol insulin per mmol glucose) than the control group (136.4+/-23.1 pmol insulin per mmol glucose; P < 0.05) and the IR-group (115.6+/-11.8 pmol insulin per mmol glucose; P = 0.05). Furthermore, the acute insulin response during the first 10 min of an intravenous glucose tolerance test was lower in the IS-group than in the IR-group. Maximal insulin secretion capacity evaluated by C-peptide levels during the hyperglycemic clamp did not differ between the groups. The IR-group had lower rates of whole body glucose uptake (60.1+/-4.6 micromol per lean body mass per minute) than did the control group (84.2+/-5.0 micromol per lean body mass per minute; P < 0.001) or the IS-group (82.6+/-5.9 micromol per lean body mass per minute; P < 0.01) and this was due to reduced glucose nonoxidation. To conclude, both impaired insulin secretion and insulin action seem to be inherited and could represent the primary defects in glucose metabolism in the offspring of NIDDM probands.

HNF-6 is expressed in endoderm derivatives and nervous system of the mouse embryo and participates to the cross-regulatory network of liver-enriched transcription factors

Hepatocyte nuclear factor-6 (HNF-6) is a liver-enriched transcription factor that contains a single cut domain and a novel type of homeodomain. Here we have studied the developmental expression pattern of HNF-6 in the mouse. In situ hybridization experiments showed that HNF-6 mRNA is detected in the liver at embryonic day (E) 9, at the onset of liver differentiation. HNF-6 mRNA disappeared transiently from the liver between E12.5 and E15. In transfection experiments HNF-6 stimulated the expression of HNF-4 and of HNF-3 beta, two transcription factors known to be involved in liver development and differentiation. HNF-6 was detected in the pancreas from E10.5 onward, where it was restricted to the exocrine cells. HNF-6 was also detected in the developing nervous system. Both the brain and the spinal cord started to express HNF-6 at E9-9.5 in postmitotic neuroblasts. Later on, HNF-6 was restricted to brain nuclei, to the retina, to the ventral horn of the spinal cord, and to dorsal root ganglia. Our observations that HNF-6 contributes to the control of the expression of transcription factors and is expressed at early stages of liver, pancreas, and neuronal differentiation suggest that HNF-6 regulates several developmental programs.