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

Targeted sequencing identifies novel variants in common and rare MODY genes

BACKGROUND

Maturity-onset diabetes of the young (MODY) is a form of monogenic diabetes with autosomal dominant inheritance. To date, mutations in 11 genes have been frequently associated with this phenotype. In Brazil, few cohorts have been screened for MODY, all using a candidate gene approach, with a high prevalence of undiagnosed cases (MODY-X).

METHODS

We conducted a next-generation sequencing target panel (tNGS) study to investigate, for the first time, a Brazilian cohort of MODY patients with a negative prior genetic analysis. One hundred and two patients were selected, of which 26 had an initial clinical suspicion of MODY-GCK and 76 were non-GCK MODY.

RESULTS

After excluding all benign and likely benign variants and variants of uncertain significance, we were able to assign a genetic cause for 12.7% (13/102) of the probands. Three rare MODY subtypes were identified (PDX1/NEUROD1/ABCC8), and eight variants had not been previously described/mapped in genomic databases. Important clinical findings were evidenced in some cases after genetic diagnosis, such as MODY-PDX1/HNF1B.

CONCLUSION

A multiloci genetic approach allowed the identification of rare MODY subtypes, reducing the large percentage of MODY-X in Brazilian cases and contributing to a better clinical, therapeutic, and prognostic characterization of these rare phenotypes.

Transcriptional Factors Mediating Retinoic Acid Signals in the Control of Energy Metabolism

Retinoic acid (RA), an active metabolite of vitamin A (VA), is important for many physiological processes including energy metabolism. This is mainly achieved through RA-regulated gene expression in metabolically active cells. RA regulates gene expression mainly through the activation of two subfamilies in the nuclear receptor superfamily, retinoic acid receptors (RARs) and retinoid X receptors (RXRs). RAR/RXR heterodimers or RXR/RXR homodimers bind to RA response element in the promoters of RA target genes and regulate their expressions upon ligand binding. The development of metabolic diseases such as obesity and type 2 diabetes is often associated with profound changes in the expressions of genes involved in glucose and lipid metabolism in metabolically active cells. RA regulates some of these gene expressions. Recently, in vivo and in vitro studies have demonstrated that status and metabolism of VA regulate macronutrient metabolism. Some studies have shown that, in addition to RARs and RXRs, hepatocyte nuclear factor 4α, chicken ovalbumin upstream promoter-transcription factor II, and peroxisome proliferator activated receptor β/δ may function as transcriptional factors mediating RA response. Herein, we summarize current progresses regarding the VA metabolism and the role of nuclear receptors in mediating RA signals, with an emphasis on their implication in energy metabolism.

Molecular diagnosis of maturity onset diabetes of the young in India

Diabetes is highly prevalent in India and the proportion of younger patients developing diabetes is on the increase. Apart from the more universally known type 1 diabetes and obesity related type 2 diabetes, monogenic forms of diabetes are also suspected to be prevalent in many young diabetic patients. The identification of the genetic basis of the disease not only guides in therapeutic decision making, but also aids in genetic counselling and prognostication. Genetic testing may establish the occurrence and frequency of early diabetes in our population. This review attempts to explore the utilities and horizons of molecular genetics in the field of maturity onset diabetes of the young (MODY), which include the commoner forms of monogenic diabetes.

Clinical features and treatment of maturity onset diabetes of the young (MODY)

Maturity onset diabetes of the young (MODY) is a heterogeneous group of disorders that result in β-cell dysfunction. It is rare, accounting for just 1%-2% of all diabetes. It is often misdiagnosed as type 1 or type 2 diabetes, as it is often difficult to distinguish MODY from these two forms. However, diagnosis allows appropriate individualized care, depending on the genetic etiology, and allows prognostication in family members. In this review, we discuss features of the common causes of MODY, as well as the treatment and diagnosis of MODY.

Examination of Rare Variants in HNF4 α in European Americans with Type 2 Diabetes

The hepatocyte nuclear factor 4-α (HNF4α) gene codes for a transcription factor which is responsible for regulating gene transcription in pancreatic beta cells, in addition to its primary role in hepatic gene regulation. Mutations in this gene can lead to maturity-onset diabetes of the young (MODY), an uncommon, autosomal dominant, non-insulin dependent form of diabetes. Mutations in HNF4α have been found in few individuals, and infrequently have they segregated completely with MODY in families. In addition, due to similarity of phenotypes, it is unclear what proportion of type 2 diabetes (T2DM) in the general population is due to MODY or HNF4α mutations specifically. In this study, 27 documented rare and common variants were genotyped in a European American population of 1270 T2DM cases and 1017 controls from review of databases and literature implicating HNF4α variants in MODY and T2DM. Seventeen variants were found to be monomorphic. Two cases and one control subject had one copy of a 6-bp P2 promoter deletion. The intron 1 variant (rs6103716; MAF = 0.31) was not significantly associated with disease status (p>0.8) and the missense variant Thr130Ile (rs1800961; MAF = 0.027) was also not significantly different between cases and controls (p>0.2), but showed a trend consistent with association with T2DM. Four variants were found to be rare as heterozygotes in small numbers of subjects. Since many variants were infrequent, a pooled chi-squared analysis of rare variants was used to assess the overall burden of variants between cases and controls. This analysis revealed no significant difference (P=0.22). We conclude there is little evidence to suggest that HNF4α variants contribute significantly to risk of T2DM in the general population, but a modest contribution cannot be excluded. In addition, the observation of some mutations in controls suggests they are not highly penetrant MODY-causing variants.

Islet cell development

Over the last years, there has been great success in driving stem cells toward insulin-expressing cells. However, the protocols developed to date have some limitations, such as low reliability and low insulin production. The most successful protocols used for generation of insulin-producing cells from stem cells mimic in vitro pancreatic organogenesis by directing the stem cells through stages that resemble several pancreatic developmental stages. Islet cell fate is coordinated by a complex network of inductive signals and regulatory transcription factors that, in a combinatorial way, determine pancreatic organ specification, differentiation, growth, and lineage. Together, these signals and factors direct the progression from multipotent progenitor cells to mature pancreatic cells. Later in development and adult life, several of these factors also contribute to maintain the differentiated phenotype of islet cells. A detailed understanding of the processes that operate in the pancreas during embryogenesis will help us to develop a suitable source of cells for diabetes therapy. In this chapter, we will discuss the main transcription factors involved in pancreas specification and beta-cell formation.

Structural basis of natural promoter recognition by a unique nuclear receptor, HNF4alpha. Diabetes gene product

HNF4alpha (hepatocyte nuclear factor 4alpha) plays an essential role in the development and function of vertebrate organs, including hepatocytes and pancreatic beta-cells by regulating expression of multiple genes involved in organ development, nutrient transport, and diverse metabolic pathways. As such, HNF4alpha is a culprit gene product for a monogenic and dominantly inherited form of diabetes, known as maturity onset diabetes of the young (MODY). As a unique member of the nuclear receptor superfamily, HNF4alpha recognizes target genes containing two hexanucleotide direct repeat DNA-response elements separated by one base pair (DR1) by exclusively forming a cooperative homodimer. We describe here the 2.0 angstroms crystal structure of human HNF4alpha DNA binding domain in complex with a high affinity promoter element of another MODY gene, HNF1alpha, which reveals the molecular basis of unique target gene selection/recognition, DNA binding cooperativity, and dysfunction caused by diabetes-causing mutations. The predicted effects of MODY mutations have been tested by a set of biochemical and functional studies, which show that, in contrast to other MODY gene products, the subtle disruption of HNF4alpha molecular function can cause significant effects in afflicted MODY patients.

Mutations in the genes encoding the transcription factors hepatocyte nuclear factor 1 alpha (HNF1A) and 4 alpha (HNF4A) in maturity-onset diabetes of the young

Maturity-onset diabetes of the young (MODY) is a monogenic form of diabetes mellitus characterized by autosomal dominant inheritance, early age of onset (often <25 years of age), and pancreatic beta-cell dysfunction. MODY is both clinically and genetically heterogeneous, with six different genes identified to date; glucokinase (GCK), hepatocyte nuclear factor-1 alpha (HNF1A, or TCF1), hepatocyte nuclear factor-4 alpha (HNF4A), insulin promoter factor-1 (IPF1 or PDX1), hepatocyte nuclear factor-1 beta (HNF1B or TCF2), and neurogenic differentiation 1 (NEUROD1). Mutations in the HNF1A gene are a common cause of MODY in the majority of populations studied. A total of 193 different mutations have been described in 373 families. The most common mutation is Pro291fs (P291fsinsC) in the polycytosine (poly C) tract of exon 4, which has been reported in 65 families. HNF4A mutations are rarer; 31 mutations reported in 40 families. Sensitivity to treatment with sulfonylurea tablets is a feature of both HNF1A and HNF4A mutations. The identification of an HNF1A or 4A gene mutation confirms a diagnosis of MODY and has important implications for clinical management.

The G115S mutation associated with maturity-onset diabetes of the young impairs hepatocyte nuclear factor 4alpha activities and introduces a PKA phosphorylation site in its DNA-binding domain

HNF4alpha (hepatocyte nuclear factor 4alpha) belongs to a complex transcription factor network that is crucial for the function of hepatocytes and pancreatic beta-cells. In these cells, it activates the expression of a very large number of genes, including genes involved in the transport and metabolism of glucose and lipids. Mutations in the HNF4alpha gene correlate with MODY1 (maturity-onset diabetes of the young 1), a form of type II diabetes characterized by an impaired glucose-induced insulin secretion. The MODY1 G115S (Gly115-->Ser) HNF4alpha mutation is located in the DNA-binding domain of this nuclear receptor. We show here that the G115S mutation failed to affect HNF4alpha-mediated transcription on apolipoprotein promoters in HepG2 cells. Conversely, in pancreatic beta-cell lines, this mutation resulted in strong impairments of HNF4alpha transcriptional activity on the promoters of LPK (liver pyruvate kinase) and HNF1alpha, with this transcription factor playing a key role in endocrine pancreas. We show as well that the G115S mutation creates a PKA (protein kinase A) phosphorylation site, and that PKA-mediated phosphorylation results in a decreased transcriptional activity of the mutant. Moreover, the G115E (Gly115-->Glu) mutation mimicking phosphorylation reduced HNF4alpha DNA-binding and transcriptional activities. Our results may account for the 100% penetrance of diabetes in human carriers of this mutation. In addition, they suggest that introduction of a phosphorylation site in the DNA-binding domain may represent a new mechanism by which a MODY1 mutation leads to loss of HNF4alpha function.

The functional Thr130Ile and Val255Met polymorphisms of the hepatocyte nuclear factor-4alpha (HNF4A): gene associations with type 2 diabetes or altered beta-cell function among Danes

HNF4A encodes an orphan nuclear receptor that plays crucial roles in regulating hepatic gluconeogenesis and insulin secretion. The aim of the present study was to examine two rare missense polymorphisms of HNF4A, Thr130Ile and Val255Met, for altered function and for association with type 2 diabetes (T2D). We have examined these polymorphisms 1) by in vitro transactivation studies and 2) by genotyping the variants in 1409 T2D patients and in 4726 glucose-tolerant Danish white subjects. When tested in COS7 cells, both the Thr130Ile and the Val255Met variants showed a significant decrease in transactivation activity compared with wild-type (73% of wild-type, P = 0.02, and 76%, P = 0.04, respectively). The Thr130Ile variant had a significantly increased carrier frequency among T2D patients compared with glucose-tolerant subjects [odds ratio, 1.26 (1.01-1.57); P = 0.04]. The rare Val255Met polymorphism had a similar frequency among T2D patients and glucose-tolerant subjects. Heterozygous glucose-tolerant carriers of the variant showed, however, decreased levels of fasting serum C-peptide (76%; P = 0.03) and decreased fasting serum triglyceride (58%; P = 0.02). In conclusion, The Thr130Ile and the Val255Met polymorphisms decrease the transcriptional activity of HNF4A, and the Thr130Ile polymorphism associates with T2D, whereas the Val255Met variant associates with a decrease in fasting serum C-peptide.

Molecular genetics and phenotypic characteristics of MODY caused by hepatocyte nuclear factor 4alpha mutations in a large European collection

AIMS/HYPOTHESIS

Heterozygous mutations in the gene of the transcription factor hepatocyte nuclear factor 4alpha (HNF-4alpha) are considered a rare cause of MODY with only 14 mutations reported to date. The description of the phenotype is limited to single families. We investigated the genetics and phenotype of HNF-4alpha mutations in a large European Caucasian collection.

METHODS

HNF-4alpha was sequenced in 48 MODY probands, selected for a phenotype of HNF-1alpha MODY but negative for HNF-1alpha mutations. Clinical characteristics and biochemistry were compared between 54 HNF-4alpha mutation carriers and 32 familial controls from ten newly detected or previously described families.

RESULTS

Mutations in HNF-4alpha were found in 14/48 (29%) probands negative for HNF-1alpha mutations. The mutations found included seven novel mutations: S34X, D206Y, E276D, L332P, I314F, L332insCTG and IVS5nt+1G>A. I314F is the first reported de novo HNF-4alpha mutation. The average age of diagnosis was 22.9 years with frequent clinical evidence of sensitivity to sulphonylureas. Beta cell function, but not insulin sensitivity, was reduced in diabetic mutation carriers compared to control subjects (homeostasis model assessment of beta cell function 29% p<0.001 vs controls). HNF-4alpha mutations were associated with lower apolipoprotein A2 (p=0.001), A1 (p=0.04) and total HDL-cholesterol (p=0.02) than in control subjects. However, in contrast to some previous reports, levels of triglycerides and apolipoprotein C3 were normal.

CONCLUSIONS/INTERPRETATION

HNF-4alpha mutations are common when no HNF-1alpha mutation is found in strictly defined MODY families. The HNF-4alpha clinical phenotype and beta cell dysfunction are similar to HNF-1alpha MODY and are associated with reduced apolipoprotein A2 levels. We suggest that sequencing of HNF-4alpha should be performed in patients with clinical characteristics of HNF-1alpha MODY in whom mutations in HNF-1alpha are not found.

Clinical characteristics, beta-cell function, HLA class II and mutations in MODY genes in non-paediatric subjects with Type 1 diabetes without pancreatic autoantibodies

OBJECTIVE

To study clinical characteristics, beta-cell function, HLA typing and mutations in the hepatocyte nuclear factor (HNF)-1alpha and HNF-4alpha genes in Type 1 diabetes mellitus (T1D) patients without pancreatic autoantibodies.

DESIGN AND METHODS

Twenty patients without pancreatic autoantibodies (Ab neg) and 20 with autoantibodies (Ab pos), age/gender matched, were included (age 17-34 years). Islet cell, glutamic acid decarboxylase, tyrosine phosphatase and insulin autoantibodies, basal and stimulated C-peptide were measured. HLA-DRB1-DQA1-DQB1 typing and screening for mutations in the HNF-1alpha and HNF-4alpha genes were performed.

RESULTS

No differences were found in clinical presentation, metabolic control and beta-cell function in the two groups (onset or after 12 months). DRB1*0301-DQA1*0501-DQB1*0201 was the most frequent haplotype in both groups but we found a higher proportion of protective T1D haplotypes and Asp(beta57) in the Ab neg group, but in all the cases in combination with susceptible T1D haplotypes. We found two previously reported polymorphisms (HNF-1alpha, Ala98Val; HNF-4alpha, Thr130Ile) in Ab neg and a new variant (Ser165Gly) in the HNF-4alpha gene in an Ab pos subject. Conclusions In a non-paediatric population with newly diagnosed T1D, the absence of islet antibodies does not imply clinical or metabolic differences when compared with those cases with islet antibodies. Despite a similar HLA-DR/DQ typing, the presence of protective alleles and molecular properties in a higher proportion in the Ab neg group suggests that these factors could modulate the presence or absence of islet antibodies. Variants in HNF-1alpha and HNF-4alpha are unlikely to be major contributors to the pathogenesis of diabetes in antibody-negative T1D.

Structural Basis for HNF-4α Activation by Ligand and Coactivator Binding

In addition to suggesting that fatty acids are endogenous ligands, our recent crystal structure of HNF-4alpha showed an unusual degree of structural flexibility in the AF-2 domain (helix alpha12). Although every molecule contained a fatty acid within its ligand binding domain, one molecule in each homodimer was in an open inactive conformation with alpha12 fully extended and colinear with alpha10. By contrast, the second molecule in each homodimer was in a closed conformation with alpha12 folded against the body of the domain in what is widely considered to be the active state. This indicates that although ligand binding is necessary, it is not sufficient to induce an activating structural transition in HNF-4alpha as is commonly suggested to occur for nuclear receptors. To further assess potential mechanisms of activation, we have solved a structure of human HNF-4alpha bound to both fatty acid ligand and a coactivator sequence derived from SRC-1. The mode of coactivator binding is similar to that observed for other nuclear receptors, and in this case, all of the molecules adopt the closed active conformation. We conclude that for HNF-4alpha, coactivator rather than ligand binding locks the active conformation.

Comparative genomic analysis of the HNF-4alpha transcription factor gene

Hepatocyte nuclear factor-4alpha (HNF-4alpha), the gene for the maturity-onset diabetes of the young type 1 (MODY1) form of type 2 diabetes mellitus (T2DM), is within the T2DM-linked region on chromosome 20q12-q13.1 and consequently, is a positional candidate gene for T2DM. Mutations in the coding region of HNF-4alpha are rare in diabetes affected subjects. Altered regulation of HNF-4alpha gene expression, controlled by distant enhancer sequences, may contribute to the development of type 2 diabetes. Comparative sequence analysis was performed between 13 kb of genomic DNA 5' to the P1 promoter sequences of the human, mouse, and rat HNF-4alpha coding sequences. Three regions, located at -10.5 kb (295 bp in length), -6.25 kb (421 bp in length), and -5.36 kb (263 bp in length), have significant sequence identity between the species. These three regions were functionally characterized using the chloramphenicol acetyltransferase (CAT) reporter assay, in which the conserved 5' regions of mouse HNF-4alpha were cloned in front of the herpes simplex virus thymidine kinase promoter driving transcription of the CAT gene. A fragment containing the 421 bp conserved region significantly increased CAT activity in differentiated rat hepatoma cells (13.7-+/-1.9-fold control), while only a modest increase in CAT activity was observed in pancreatic cells (2.5-+/-0.9-fold control; 1.6-+/-0.1-fold control) and dedifferentiated hepatoma cells (1.7-+/-0.4-fold control). The remaining two conserved regions increased CAT activity minimally in pancreatic (1.1-+/-0.1-fold control to 1.9-+/-0.1-fold control) and hepatic (1.6-+/-0.5-fold control to 2.3-+/-0.4-fold control) cell lines. Denaturing high-performance liquid chromatography (DHPLC) was used to search for sequence variants in DNA from 259 T2DM individuals. Two single nucleotide polymorphisms (SNPs) were identified, both of which increased CAT activity in the insulinoma cell lines in the CAT reporter assay (1.4-fold increase over wild-type; 1.7-fold increase over wild-type). These results suggest that comparative sequence analysis can efficiently identify regulatory elements and that sequence variants in regulatory elements of HNF-4alpha can contribute to altered HNF-4alpha gene expression.

T130I mutation in HNF-4alpha gene is a loss-of-function mutation in hepatocytes and is associated with late-onset Type 2 diabetes mellitus in Japanese subjects

AIMS/HYPOTHESIS

Mutations in hepatocyte nuclear factor (HNF)-4alpha gene cause a form of maturity-onset diabetes of the young (MODY1). The T130I mutation is a rare missense mutation, which affects a conserved amino acid in a DNA binding domain. This mutation can be found in the general population, so this variant alone does not cause MODY. However, its significance in the development of late-onset Type 2 diabetes is not known.

METHODS

We screened 423 unrelated Japanese patients with late-onset Type 2 diabetes and 354 unrelated non-diabetic control subjects for the T130I mutation in the HNF-4alpha gene. The transactivation ability of T130I-HNF-4alpha was assessed using reporter gene assay.

RESULTS

The frequency of the T130I mutation was higher in Type 2 diabetic patients ( p=0.015, odds ratio 4.3, 95%CI 1.24-14.98) than control subjects. The serum HDL-cholesterol concentration was lower in Type 2 diabetic patients with the T130I mutation compared with those without this mutation ( p=0.006). Reporter gene analysis showed that T130I-HNF-4alpha transcriptional activity was not impaired compared with wild-type HNF-4alpha in Hela and MIN6 cells, but it was reduced in HepG2 and primary cultured mouse hepatocytes (27-78% of wild type, p<0.05).

CONCLUSION/INTERPRETATION

Our findings suggest that T130I-HNF-4alpha is a loss-of-function mutation in hepatocytes and that this mutation is associated with late-onset Type 2 diabetes in Japanese subjects. The T130I mutation in the HNF-4alpha gene might be involved in the development of Type 2 diabetes in the Japanese population.

Determinants of the development of diabetes (maturity-onset diabetes of the young-3) in carriers of HNF-1alpha mutations: evidence for parent-of-origin effect

OBJECTIVE

To determine the distribution of the age at onset of diabetes (maturity-onset diabetes of the young-3 [MODY3]) and to identify determinants of the onset of diabetes in carriers of HNF-1alpha mutations.

RESEARCH DESIGN AND METHODS

Extended families (n = 104) with type 2 diabetes inherited in a dominant pattern were recruited and screened for diabetes-causing mutations in HNF-1alpha.

RESULTS

HNF-1alpha mutations cosegregated with diabetes in only 13 families, all with a mean age at onset <35 years. Insulin secretion was diminished or absent in mutation carriers (n = 101), and diabetes developed in 65% by age 25 years and in 100% by age 50 years. If the mutation was inherited from the mother, diabetes onset was very young in those exposed to diabetes in utero; 57 +/- 8% were affected by age 15 years as compared with 0.0% in those not exposed (P < 7 x 10(-6)). By age 25 years, the difference was reduced (85 +/- 6 and 55 +/- 12%, respectively; P = 0.02). If the mutation was inherited from the father, diabetes developed in 52 +/- 8% by age 25 years. Age at diagnosis was shown to be highly heritable (h(2) = 0.47, P = 0.003). When parent of origin was included in the analyses, the magnitude of genetic contribution increased markedly (h(2) = 0.91).

CONCLUSIONS

Mutations in HNF-1alpha accounts for diabetes in a small proportion of families with a dominant pattern of inheritance. Age at onset of diabetes in MODY3 families varied widely and was influenced by familial factors (including modifying genes) and parent of origin (whether a mutation carrier was exposed to diabetes in utero).

Activation of the insulin gene promoter through a direct effect of hepatocyte nuclear factor 4 alpha

Maturity onset diabetes of the young, subtype 1 (MODY1), is associated with defective glucose-dependent insulin secretion from pancreatic beta cells. MODY1 is caused by mutation in the transcription factor hepatocyte nuclear factor 4 alpha (HNF4 alpha). To understand better the MODY1 phenotype, we tested whether HNF4 alpha was able to modulate directly the insulin gene promoter. Transfection of cultured 293T cells with an HNF4 alpha expression vector led to 10-fold activation of a cotransfected reporter plasmid containing the rat insulin I gene promoter. Computer analysis revealed a potential HNF4 alpha-binding site between nucleotides -57 and -69 of the promoter; mutation of this sequence led to reduced ability of HNF4 alpha to activate the promoter. The ability of HNF4 alpha to bind this sequence was confirmed using gel shift analysis. In transfected INS-1 beta cells, mutation of either the HNF1 alpha site or the HNF4 alpha site in the insulin gene promoter led to 50-75% reduction in reporter gene activity; expression of dominant negative HNF4 alpha led to significant reduction in the activity of wild type and both mutated promoters. Thus, in addition to the previously described indirect action of HNF4 alpha on insulin gene expression mediated through elevated HNF1 alpha levels, HNF4 alpha also activates the insulin gene directly, through a previously unrecognized cis element.

Molecular etiologies of MODY and other early-onset forms of diabetes

Maturity-onset diabetes of the young (MODY) are monogenic forms of type 2 diabetes that are characterized by an early disease onset, autosomal-dominant inheritance, and defects in insulin secretion. Genetic studies have identified mutations in at least eight genes associated with different forms of MODY. The majority of the MODY subtypes are caused by mutations in transcription factors that include hepatocyte nuclear factor (HNF)-4 alpha, HNF-1 alpha, PDX-1, HNF-1 beta, and NEURO-DI/BETA-2. In addition, genetic defects in the glucokinase gene, the glucose sensor of the pancreatic beta cells, and the insulin gene also lead to impaired glucose tolerance. Biochemical and genetic studies have demonstrated that the MODY genes are functionally related and form an integrated transcriptional network that is important for many metabolic pathways.

A novel mutation in the hepatocyte nuclear factor-1alpha/MODY3 gene in Chinese subjects with early-onset Type 2 diabetes mellitus in Taiwan

AIMS

The goal of this study was to determine the frequency of mutation in hepatic nuclear factor (HNF)-1alpha, a gene recently implicated as causing maturity-onset diabetes of the young (MODY) and to analyse the respective clinical presentations in an ethnically Chinese population.

METHODS

Fifteen unrelated subjects (nine females and six males) aged less than 35 years who had early-onset diabetes were analysed to test the possibility that mutation of the HNF-1alpha gene was responsible for this disorder. Genomic DNA extraction, polymerase chain reaction and DNA sequence analysis were performed accordingly.

RESULTS

One patient with MODY had a novel missense mutation in exon 3 of the HNF-1alpha gene (Y218C) in a region of the protein that corresponds to a predicted DNA binding domain.

CONCLUSIONS

A Y218C mutation in HNF-1alpha gene was identified in one family in Taiwan.

Naturally occurring mutations in the human HNF4alpha gene impair the function of the transcription factor to a varying degree

The hepatocyte nuclear factor (HNF)4alpha, a member of the nuclear receptor superfamily, regulates genes that play a critical role in embryogenesis and metabolism. Recent studies have shown that mutations in the human HNF4alpha gene cause a rare form of type 2 diabetes, maturity onset diabetes of the young (MODY1). To investigate the properties of these naturally occurring HNF4alpha mutations we analysed five MODY1 mutations (R154X, R127W, V255M, Q268X and E276Q) and one other mutation (D69A), which we found in HepG2 hepatoma cells. Activation of reporter genes in transfection assays and DNA binding studies showed that the MODY1-associated mutations result in a variable reduction in function, whereas the D69A mutation showed an increased activity on some promoters. None of the MODY mutants acted in a dominant negative manner, thus excluding inactivation of the wild-type factor as a critical event in MODY development. A MODY3-associated mutation in the HNF1alpha gene, a well-known target gene of HNF4alpha, results in a dramatic loss of the HNF4 binding site in the promoter, indicating that mutations in the HNF4alpha gene might cause MODY through impaired HNF1alpha gene function. Based on these data we propose a two-hit model for MODY development.