A hepatocyte nuclear factor-4 alpha gene (HNF4A) P2 promoter haplotype linked with late-onset diabetes: studies of HNF4A variants in the Norwegian MODY registry

Whole Exome Sequencing in Children With Type 1 Diabetes Before Age 6 Years Reveals Insights Into Disease Heterogeneity

Aims: This study is aimed at comparing whole exome sequencing (WES) data with the clinical presentation in children with type 1 diabetes onset ≤ 5 years of age (EOT1D). Methods: WES was performed in 99 unrelated children with EOT1D with subsequent analysis to identify potentially deleterious rare variants in MODY genes. High-resolution HLA class II haplotyping, SNP genotyping, and T1D-genetic risk score (T1D-GRS) were also evaluated. Results: Eight of the ninety-nine EOT1D participants carried a potentially deleterious rare variant in a MODY gene. Rare variants affected five genes: GCK (n = 1), HNF1B (n = 2), HNF4A (n = 1), PDX1 (n = 2), and RFX6 (n = 2). At diagnosis, these children had a mean age of 3.0 years, a mean HbA1c of 10.5%, a detectable C-peptide in 5/8, and a positive islet autoantibody in 6/7. Children with MODY variants tend to exhibit a lower number of pancreatic autoantibodies and a lower fasting C-peptide compared to EOT1D without MODY rare variants. They also carried at least one high-risk DR3-DQ2 or DR4-DQ8 haplotype and exhibited a T1D-GRS similar to the other individuals in the EOT1D cohort, but higher than healthy controls. Conclusions: WES found potentially deleterious rare variants in MODY genes in 8.1% of EOT1D, occurring in the context of a T1D genetic background. Such genetic variants may contribute to disease precipitation by a β-cell dysfunction mechanism. This supports the concept of different endotypes of T1D, and WES at T1D onset may be a prerequisite for the implementation of precision therapies in children with autoimmune diabetes.

Plasma Proteins Associated with Chronic Histopathologic Lesions on Kidney Biopsy

Key Points

Proteomic profiling identified 35 blood proteins associated with chronic histopathologic lesions in the kidney. Testican-2 was expressed in the glomerulus, released by the kidney into circulation, and inversely associated with glomerulosclerosis severity. NELL1 was expressed in tubular epithelial cells, released by the kidney into circulation, and inversely associated with interstitial fibrosis and tubular atrophy severity.

Background

The severity of chronic histopathologic lesions on kidney biopsy is independently associated with higher risk of progressive CKD. Because kidney biopsies are invasive, identification of blood markers that report on underlying kidney histopathology has the potential to enhance CKD care.

Methods

We examined the association between 6592 plasma protein levels measured by aptamers and the severity of interstitial fibrosis and tubular atrophy (IFTA), glomerulosclerosis, arteriolar sclerosis, and arterial sclerosis among 434 participants of the Boston Kidney Biopsy Cohort. For proteins significantly associated with at least one histologic lesion, we assessed renal arteriovenous protein gradients among 21 individuals who had undergone invasive catheterization and assessed the expression of the cognate gene among 47 individuals with single-cell RNA sequencing data in the Kidney Precision Medicine Project.

Results

In models adjusted for eGFR, proteinuria, and demographic factors, we identified 35 proteins associated with one or more chronic histologic lesions, including 20 specific for IFTA, eight specific for glomerulosclerosis, and one specific for arteriolar sclerosis. In general, higher levels of these proteins were associated with more severe histologic score and lower eGFR. Exceptions included testican-2 and NELL1, which were associated with less glomerulosclerosis and IFTA, respectively, and higher eGFR; notably, both of these proteins demonstrated significantly higher levels from artery to renal vein, demonstrating net kidney release. In the Kidney Precision Medicine Project, 13 of the 35 protein hits had cognate gene expression enriched in one or more cell types in the kidney, including podocyte expression of select glomerulosclerosis markers (including testican-2) and tubular expression of several IFTA markers (including NELL1).

Conclusions

Proteomic analysis identified circulating proteins associated with chronic histopathologic lesions, some of which had concordant site-specific expression within the kidney.

Molecular mechanism of HNF-1A-mediated HNF4A gene regulation and promoter-driven HNF4A-MODY diabetes

Monogenic diabetes is a gateway to precision medicine through molecular mechanistic insight. Hepatocyte nuclear factor 1A (HNF-1A) and HNF-4A are transcription factors that engage in crossregulatory gene transcription networks to maintain glucose-stimulated insulin secretion in pancreatic β cells. Variants in the HNF1A and HNF4A genes are associated with maturity-onset diabetes of the young (MODY). Here, we explored 4 variants in the P2-HNF4A promoter region: 3 in the HNF-1A binding site and 1 close to the site, which were identified in 63 individuals from 21 families of different MODY disease registries across Europe. Our goal was to study the disease causality for these variants and to investigate diabetes mechanisms on the molecular level. We solved a crystal structure of HNF-1A bound to the P2-HNF4A promoter and established a set of techniques to probe HNF-1A binding and transcriptional activity toward different promoter variants. We used isothermal titration calorimetry, biolayer interferometry, x-ray crystallography, and transactivation assays, which revealed changes in HNF-1A binding or transcriptional activities for all 4 P2-HNF4A variants. Our results suggest distinct disease mechanisms of the promoter variants, which can be correlated with clinical phenotype, such as age of diagnosis of diabetes, and be important tools for clinical utility in precision medicine.

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.

Novel mechanisms of regulation of the expression and transcriptional activity of hepatocyte nuclear factor 4α

Hepatocyte nuclear factor 4α (HNF4α) is a master regulator of development and function of digestive tissues. The HNF4A gene uses two separate promoters P1 and P2, with P1 products predominant in adult liver, whereas P2 products prevalent in fetal liver, pancreas, and liver/colon cancer. To date, the mechanisms for the regulation of HNF4A and the dynamic switch of P1-HNF4α and P2-HNF4α during ontogenesis and carcinogenesis are still obscure. Our study validated the previously reported self-stimulation of P1-HNF4α but invalidated the reported synergism between HNF4α and HNF1α. HNF4A-AS1, a long noncoding RNA, is localized between the P2 and P1 promoters of HNF4A. We identified critical roles of P1-HNF4α in regulating the expression of HNF4A-AS1 and its mouse ortholog Hnf4a-os. Paired box 6 (PAX6), a master regulator of pancreas development overexpressed in colon cancer, cooperated with HNF1α to induce P2-HNF4α but antagonized HNF4α in HNF4A-AS1 expression. Thus, PAX6 may be important in determining ontogenic and carcinogenic changes of P2-HNF4α and HNF4A-AS1 in the pancreas and intestine. We also interrogated transactivation activities on multiple gene targets by multiple known and novel HNF4α mutants identified in patients with maturity onset diabetes of the young 1 (MODY1) and liver cancer. Particularly, HNF4α-D78A and HNF4α-G79S, two mutants found in liver cancer with mutations in DNA-binding domain, displayed highly gene-specific transactivation activities. Interestingly, HNF4α-Q277X, a MODY1 truncation mutant, antagonized the transactivation activities of HNF1α and farnesoid X receptor, key regulators of insulin secretion. Taken together, our study provides novel mechanistic insights regarding the transcriptional regulation and transactivation activity of HNF4α in digestive tissues.

Lessons from whole-exome sequencing in MODYX families

We report the first results from whole-exome sequencing performed in families with Maturity-Onset Diabetes of the Young without a known genetic cause of diabetes (MODYX). This next generation sequencing technique pointed out that routine testing of MODY needs constant awareness and regular re-evaluation of both clinical criteria and primer sequences.

Detection and characterization of two novel mutations in the HNF4A gene in maturity-onset diabetes of the young type 1 in two Japanese families

BACKGROUND

Maturity-onset diabetes of the young (MODY) is a subgroup of monogenic diabetes mellitus, of which MODY1, caused by HNF4A mutations, accounts for only 5% or less and has been rarely reported in East Asian countries. Here we report two novel HNF4A mutations in two Japanese families with MODY1.

METHODS

Proband 1 is an 8-year-old girl and proband 2 is a 14-year-old girl. Both were nonobese, demonstrated elevated HbA1c and negative serum anti-glutamic acid decarboxylase antibodies, and had a family history of diabetes. We directly sequenced HNF4A and performed functional analysis of the detected missense mutation.

RESULTS

Proband 1 had a heterozygous missense mutation, c.824A>G (p.Asn275Ser). Luciferase assay demonstrated a significant reduction in transcriptional activity. A heterozygous frame shift mutation, c.692-695delAGGA (p.Lys231ThrfsX5), was detected in proband 2. Affected family members shared the same mutations, showing high penetrance. Both mutations reside in the HNF4α dimerization domain and the corresponding amino acids are well conserved between species.

CONCLUSIONS

These two mutations are most likely the cause of MODY1 in these families. Considering the effectiveness of sulfonylureas, it is important to correctly diagnose MODY1.

Assessing the phenotypic effects in the general population of rare variants in genes for a dominant Mendelian form of diabetes

Genome sequencing can identify individuals in the general population who harbor rare coding variants in genes for Mendelian disorders and who may consequently have increased disease risk. Previous studies of rare variants in phenotypically extreme individuals display ascertainment bias and may demonstrate inflated effect-size estimates. We sequenced seven genes for maturity-onset diabetes of the young (MODY) in well-phenotyped population samples (n = 4,003). We filtered rare variants according to two prediction criteria for disease-causing mutations: reported previously in MODY or satisfying stringent de novo thresholds (rare, conserved and protein damaging). Approximately 1.5% and 0.5% of randomly selected individuals from the Framingham and Jackson Heart Studies, respectively, carry variants from these two classes. However, the vast majority of carriers remain euglycemic through middle age. Accurate estimates of variant effect sizes from population-based sequencing are needed to avoid falsely predicting a substantial fraction of individuals as being at risk for MODY or other Mendelian diseases.

Atypical phenotype associated with reported GCK exon 10 deletions: Clinical judgement is needed alongside appropriate genetic investigations

BACKGROUND

Maturity-onset diabetes of the young (MODY) caused by heterozygous mutations in the glucokinase (GCK) gene typically presents with lifelong, stable, mild fasting hyperglycaemia. With the exception of pregnancy, patients with GCK-MODY usually do not require pharmacological therapy. We report two unrelated patients whose initial genetic test results indicated a deletion of GCK exon 10, but whose clinical phenotypes were not typical of GCK-MODY.

CASE REPORTS

In case 1, the patient was hyperglycaemic at diagnosis (glucose > 30 mmol/l) and elevated glucose levels > 10 mmol/l persisted after withdrawal of insulin therapy. The patient in case 2 was also hyperglycaemic at diagnosis [HbA1c > 86 mmol/mol (10%)], which improved with the introduction of oral hypoglycaemic agents. These clinical features were not consistent with GCK-MODY. Both patients had a single nucleotide variant that prevented multiplex ligation-dependent probe analysis, which generated a false positive result of a GCK exon 10 deletion.

CONCLUSION

False positive genetic results in these two unrelated cases were attributable to the presence of a rare single nucleotide variant that prevented ligation of the probe in the multiplex ligation-dependent probe analysis kit used and falsely indicated deletion of exon 10 within GCK. Both cases had clinical features that did not tally with the typical GCK-MODY phenotype. These cases emphasize the need to interpret the results of definitive genetic tests within the specific clinical context. Increased medical sequencing is likely to lead to more reports of novel mutations of uncertain significance. If genetic investigations do not agree with the clinical picture, clinicians should exercise caution when making therapeutic changes based on these results.

Mutations in the genes encoding the transcription factors hepatocyte nuclear factor 1 alpha and 4 alpha in maturity-onset diabetes of the young and hyperinsulinemic hypoglycemia

Maturity-onset diabetes of the young (MODY) is a monogenic disorder characterized by autosomal dominant inheritance of young-onset (typically <25 years), noninsulin-dependent diabetes due to defective insulin secretion. MODY is both clinically and genetically heterogeneous with mutations in at least 10 genes. Mutations in the HNF1A gene encoding hepatocyte nuclear factor-1 alpha are the most common cause of MODY in most adult populations studied. The number of different pathogenic HNF1A mutations totals 414 in 1,247 families. Mutations in the HNF4A gene encoding hepatocyte nuclear factor-4 alpha are a rarer cause of MODY with 103 different mutations reported in 173 families to date. Sensitivity to treatment with sulfonylurea tablets is a feature of both HNF1A and HNF4A mutations. The HNF4A MODY phenotype has been expanded by the reports of macrosomia in ∼50% of babies, and more rarely, neonatal hyperinsulinemic hypoglycemia. The identification of an HNF1A or HNF4A gene mutation has important implications for clinical management in diabetes and pregnancy, but MODY is significantly underdiagnosed. Current research is focused on identifying biomarkers and developing probability models to identify those patients most likely to have MODY, until next generation sequencing technology enables cost-effective gene analysis for all patients with young onset diabetes.

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.

Disease progression and search for monogenic diabetes among children with new onset type 1 diabetes negative for ICA, GAD- and IA-2 Antibodies

BACKGROUND

To investigate disease progression the first 12 months after diagnosis in children with type 1 diabetes negative (AAB negative) for pancreatic autoantibodies [islet cell autoantibodies(ICA), glutamic acid decarboxylase antibodies (GADA) and insulinoma-associated antigen-2 antibodies (IA-2A)]. Furthermore the study aimed at determining whether mutations in KCNJ11, ABCC8, HNF1A, HNF4A or INS are common in AAB negative diabetes.

MATERIALS AND METHODS

In 261 newly diagnosed children with type 1 diabetes, we measured residual β-cell function, ICA, GADA, and IA-2A at 1, 6 and 12 months after diagnosis. The genes KCNJ11, ABCC8, HNF1A, HNF4A and INS were sequenced in subjects AAB negative at diagnosis. We expressed recombinant K-ATP channels in Xenopus oocytes to analyse the functional effects of an ABCC8 mutation.

RESULTS

Twenty-four patients (9.1%) tested AAB negative after one month. Patients, who were AAB-negative throughout the 12-month period, had higher residual β-cell function (P = 0.002), lower blood glucose (P = 0.004), received less insulin (P = 0.05) and had lower HbA1c (P = 0.02) 12 months after diagnosis. One patient had a heterozygous mutation leading to the substitution of arginine at residue 1530 of SUR1 (ABCC8) by cysteine. Functional analyses of recombinant K-ATP channels showed that R1530C markedly reduced the sensitivity of the K-ATP channel to inhibition by MgATP. Morover, the channel was highly sensitive to sulphonylureas. However, there was no effect of sulfonylurea treatment after four weeks on 1.0-1.2 mg/kg/24 h glibenclamide.

CONCLUSION

GAD, IA-2A, and ICA negative children with new onset type 1 diabetes have slower disease progression as assessed by residual beta-cell function and improved glycemic control 12 months after diagnosis. One out of 24 had a mutation in ABCC8, suggesting that screening of ABCC8 should be considered in patients with AAB negative type 1 diabetes.

Variants in hepatocyte nuclear factor 4alpha gene promoter region and type 2 diabetes risk in Chinese

As a key regulator of insulin secretion and metabolism of glucose, cholesterol and fatty acid, hepatocyte nuclear factor 4alpha (HNF4A) was suggested as a candidate gene for type 2 diabetes (T2D); however, no association study between HNF4A and T2D in the Chinese population has been conducted before. To address this issue, we evaluated the impact of the HNF4A variants (rs1884614 and rs2425637) on T2D and metabolic traits in 1912 unrelated patients and 2041 control subjects in the Chinese Han population. Our results suggested that no individual single nucleotide polymorphisms of HNF4A was significantly associated with T2D at either allele or genotype level. However, rs2425637 in the promoter region of HNF4A was found to have an effect on total cholesterol and high-density lipoprotein before multiple testing correction. To summarize, our investigation did not confirm the effects of HNF4A variants (rs1884614 and rs2425637) on T2D risk, but found that the risk HNF4A contributed to T2D might be population specific.

[Progress in diabetes genetics]

BACKGROUND

Diabetes is classified as Type 1 diabetes, Type 2 diabetes, gestational diabetes and other types. Our goal was to provide an overview of new genetic knowledge of monogenic and type 2 diabetes.

MATERIAL AND METHOD

The article is based on literature identified through a non-systematic search in PubMed and own experience concerning research in diabetes genetics and treatment of patients with monogenic diabetes.

RESULTS

18 genes have been found for which one single mutation may cause diabetes. The most common causes for such monogenic diabetes are mutations in the genes KCNJ11, ABCC8 and INS when the condition is diagnosed at the age 0 - 6 months, and in the genes HNF1A, GCK, HNF4A and HNF1B when the diagnosis is made later than six months of age. Genetic testing is appropriate in assessment of monogenic diabetes, because antidiabetic tablets rather that insulin injections can be used to treat patients with mutations in certain genes; i.e. KCNJ11, ABCC8, HNF1A and HNF4A. Genome-wide association studies have recently identified about 20 genetic variants that increase the risk of Type 2 diabetes, but which have a low predictive value for development of disease. How these genetic variants can cause Type 2 diabetes has not been assessed and clinical relevance remains to be shown.

INTERPRETATION

So far, genetic findings only affect diagnosis and treatment of monogenic diabetes.

Novel monogenic diabetes mutations in the P2 promoter of the HNF4A gene are associated with impaired function in vitro

AIMS

Mutations in HNF4A cause a form of monogenic beta-cell diabetes. We aimed to identify mutations in the pancreas-specific P2 promoter of HNF4A in families with suspected HNF4A diabetes and to show that they impaired the function of the promoter in vitro.

METHODS

We screened families with a clinical suspicion of HNF4A monogenic beta-cell diabetes for mutations in the HNF4A P2 promoter. We investigated the function of the previously reported HNF4A P2 promoter mutation -192C>G linked to late-onset diabetes in several families, along with two new segregating mutations, in vitro using a modified luciferase reporter assay system with enhanced sensitivity.

RESULTS

We identified two novel HNF4A P2 promoter mutations that co-segregate with diabetes in two families, -136A>G and -169C>T. Both families displayed phenotypes typical of HNF4A monogenic beta-cell diabetes, including at least two affected generations, good response to sulphonylurea treatment and increased birthweight and/or neonatal hypoglycaemia. We show that both of these novel mutations and -192C>G impair the function of the promoter in transient transfection assays.

CONCLUSIONS

Two novel mutations identified here and the previously identified late-onset diabetes mutation, -192C>G, impair the function of the HNF4A P2 promoter in vitro.

Investigating parent of origin effects in studies of type 2 diabetes and obesity

The role of parent-of-origin effects (POE) in the etiology of complex diseases such as type 2 diabetes (T2DM) and obesity is currently of intense interest, but still largely unclear. POE are transmittable genetic effects whereby the expression of the phenotype in the offspring depends upon whether the transmission originated from the mother or father. In mammals, POE can be caused by genetic imprinting, intrauterine effects, or maternally inherited mitochondrial genes. In this paper, we describe the different mechanisms underlying POE, characterize known examples of POE in rare forms of diabetes, and review the evidence from linkage and association studies for POE in T2DM and obesity. Finally, we summarize some of the new and established statistical and experimental approaches commonly used to detect POE. Through this paper, we hope emphasizes the potentially significant importance of POE in the etiology of T2DM and obesity.

Diagnostic screening of MODY2/GCK mutations in the Norwegian MODY Registry

BACKGROUND

Maturity-onset diabetes of the young, type 2 (MODY2) is caused by mutations in the glucokinase gene (GCK). The aim of our study was to determine the prevalence of GCK mutations in the Norwegian MODY Registry and to delineate the clinical phenotype of identified GCK mutation carriers.

METHODS

We screened 122 probands referred to the MODY Registry for mutations in GCK and studied extended families with MODY2.

RESULTS

We found 2 novel (S76Y and N231S) and 13 previously reported (V62A, G72R, L146R, R191W, A208T, M210K, Y215X, M235T, R275C, E339G, R377C, S453L, and IVS5+1G>C) GCK mutations in 23 probands and in their 33 family members. The prevalence of MODY2 was 12% in the Norwegian MODY Registry. The subjects with GCK mutations had features of mild diabetes. Yet, 15 of 56 MODY2 subjects were treated with oral drugs or insulin. Three subjects had retinopathy and one had macrovascular disease. Also, a limited number of cases had elevated fasting serum triglyceride values. Moreover, two GCK mutation carriers were diagnosed with type 1 diabetes.

CONCLUSIONS

According to our diagnostic screening of GCK in the MODY Registry, MODY2 is less prevalent than MODY3 in Norway but is likely to be underreported. Recognizing MODY2 in diabetic patients is important in order to prevent overtreatment. Finally, our study demonstrates the co-occurrence of MODY2 in families with type 1 or type 2 diabetes.

Prevalence of HNF1A (MODY3) mutations in a Norwegian population (the HUNT2 Study)

AIMS

Previous reports have indicated that maturity-onset diabetes of the young (MODY) caused by hepatocyte nuclear factor 1A (HNF1A) mutations (MODY3) is the most common MODY subtype in Northern Europe, but population-based prevalence estimates are lacking. We sought to determine the prevalence of HNF1A-MODY in diabetic subjects of a defined Norwegian population (the HUNT2 Study).

METHODS

Of the 1972 diabetic HUNT2 subjects, we identified a subgroup of 43 suspected MODY cases based on information on family history, disease onset and anti-glutamic acid decarboxylase autoantibody status. These cases were considered a discovery group for HNF1A mutations and underwent full DNA sequencing. Subsequently, the entire cohort of diabetic HUNT2 subjects was screened for three selected HNF1A mutations. Possible founder effects were examined using the Norwegian MODY Registry.

RESULTS

Three subjects from the discovery group harboured HNF1A mutations. Two subjects had the previously described R229Q mutation, one had a novel S6N alteration, whereas the HNF1A hot-spot mutation P291fsinsC was not identified. Genotyping the cohort of diabetic HUNT2 subjects identified five additional R229Q-positive subjects. Microsatellite analysis performed for all R229Q-positive probands of the Norwegian MODY Registry and those found in the HUNT2 population revealed that 17 of 18 (94%) had genotypes consistent with a common haplotype.

CONCLUSIONS

Clinical MODY criteria were fulfilled in 2.2% of diabetic HUNT2 subjects. The minimum prevalence of HNF1A-MODY among diabetic HUNT2 subjects was 0.4%. Because of founder effects, registry-based prevalence studies probably need to be very large and they should also include prospectively collected phenotypes and extensive mutation screening to establish the true prevalence of MODY.

The diabetic phenotype in HNF4A mutation carriers is moderated by the expression of HNF4A isoforms from the P1 promoter during fetal development

OBJECTIVE

Mutations in the alternatively spliced HNF4A gene cause maturity-onset diabetes of the young (MODY). We characterized the spatial and developmental expression patterns of HNF4A transcripts in human tissues and investigated their role as potential moderators of the MODY phenotype.

RESEARCH DESIGN AND METHODS

We measured the expression of HNF4A isoforms in human adult tissues and gestationally staged fetal pancreas by isoform-specific real-time PCR. The correlation between mutation position and age of diagnosis or age-related penetrance was assessed in a cohort of 190 patients with HNF4A mutations.

RESULTS

HNF4A was expressed exclusively from the P2 promoter in adult pancreas, but from 9 weeks until at least 26 weeks after conception, up to 23% of expression in fetal pancreas was of P1 origin. HNF4A4-6 transcripts were not detected in any tissue. In whole pancreas, HNF4A9 expression was greater than in islets isolated from the endocrine pancreas (relative level 22 vs. 7%). Patients with mutations in exons 9 and 10 (absent from HNF4A3, HNF4A6, and HNF4A9 isoforms) developed diabetes later than those with mutations in exons 2-8, where all isoforms were affected (40 vs. 24 years; P = 0.029). Exon 9/10 mutations were also associated with a reduced age-related penetrance (53 vs. 10% without diabetes at age 55 years; P < 0.00001).

CONCLUSIONS

We conclude that isoforms derived from the HNF4A P1 promoter are expressed in human fetal, but not adult, pancreas, and that their presence during pancreatic development may moderate the diabetic phenotype in individuals with mutations in the HNF4A gene.

Best practice guidelines for the molecular genetic diagnosis of maturity-onset diabetes of the young

AIMS/HYPOTHESIS

Mutations in the GCK and HNF1A genes are the most common cause of the monogenic forms of diabetes known as 'maturity-onset diabetes of the young'. GCK encodes the glucokinase enzyme, which acts as the pancreatic glucose sensor, and mutations result in stable, mild fasting hyperglycaemia. A progressive insulin secretory defect is seen in patients with mutations in the HNF1A and HNF4A genes encoding the transcription factors hepatocyte nuclear factor-1 alpha and -4 alpha. A molecular genetic diagnosis often changes management, since patients with GCK mutations rarely require pharmacological treatment and HNF1A/4A mutation carriers are sensitive to sulfonylureas. These monogenic forms of diabetes are often misdiagnosed as type 1 or 2 diabetes. Best practice guidelines for genetic testing were developed to guide testing and reporting of results.

METHODS

A workshop was held to discuss clinical criteria for testing and the interpretation of molecular genetic test results. The participants included 22 clinicians and scientists from 13 countries. Draft best practice guidelines were formulated and edited using an online tool (http://www.coventi.com).

RESULTS

An agreed set of clinical criteria were defined for the testing of babies, children and adults for GCK, HNF1A and HNF4A mutations. Reporting scenarios were discussed and consensus statements produced.

CONCLUSIONS/INTERPRETATION

Best practice guidelines have been established for monogenic forms of diabetes caused by mutations in the GCK, HNF1A and HNF4A genes. The guidelines include both diagnostic and predictive genetic tests and interpretation of the results.

Studies in 3,523 Norwegians and meta-analysis in 11,571 subjects indicate that variants in the hepatocyte nuclear factor 4 alpha (HNF4A) P2 region are associated with type 2 diabetes in Scandinavians

OBJECTIVE

Recent publications have found an association between common variants near the hepatocyte nuclear factor 4 alpha (HNF4A) P2 promoter and type 2 diabetes in some populations but not in others, and the role for HNF4A in type 2 diabetes has remained unclear. In an attempt to address these inconsistencies, we investigated HNF4A single nucleotide polymorphisms (SNPs) in a large population-based sample and included a meta-analysis of published studies.

RESEARCH DESIGN AND METHODS

We genotyped 12 SNPs in the HNF4A region in a Norwegian population-based sample of 1,644 individuals with type 2 diabetes and 1,879 control subjects (the Nord-Trøndelag Health Study [HUNT] 2). We combined our data with all previously published case/control studies and performed a meta-analysis.

RESULTS

Consistent with initial studies, we found a trend toward association for the SNPs rs1884613 (odds ratio [OR] 1.17 [95% CI 1.03-1.35]) and rs2144908 (1.21 [1.05-1.38]) in the P2 region and for rs4812831 (1.21 [1.02-1.44]), located 34 kb downstream of the P2 promoter. Meta-analysis, comprising 12,292 type 2 diabetic case and 15,519 control subjects, revealed a nonsignificant OR of 1.05 (95% CI 0.98-1.12) but with significant heterogeneity between the populations. We therefore performed a subanalysis including only the data for subjects from Scandinavia. Among the 4,000 case and 7,571 control Scandinavian subjects, a pooled OR of 1.14 (1.06-1.23), P = 0.0004, was found for the SNP rs1884613.

CONCLUSIONS

Our results suggest that variation in the HNF4A region is associated with type 2 diabetes in Scandinavians, highlighting the importance of exploring small genetic effects in large, homogenous populations.

HNF4A genetic variants: role in diabetes

PURPOSE OF REVIEW

Variants in the hepatocyte nuclear factor 4alpha (HNF4A) gene play a role in the development of diabetes mellitus. Although genetic variation in and around HNF4A regulatory regions has received considerable attention, the significance of these variants in the common type 2 diabetes varies in the literature. This review will provide a general overview of recent genetic studies involving the evaluation of HNF4A as a contributor to the risk and pathophysiology of diabetes mellitus and related risk factors.

RECENT FINDINGS

These studies report newly identified variants, evaluate previously reported polymorphisms that were associated with type 2 diabetes in several distinct populations with maturity-onset diabetes of the young, type 2 diabetes, gestational diabetes, and diabetes related risk factors, and propose a role for HNF4A in insulin secretion via the potassium ATP channel.

SUMMARY

HNF4A variants identified so far appear to modestly contribute to predisposition for type 2 diabetes. Continued identification and especially functional characterization of variants, however, will be critical in future studies to enhance our understanding of the metabolic impact of this gene.

Insights on pathogenesis of type 2 diabetes from MODY genetics

Maturity-onset diabetes of the young (MODY) is a type of non-insulin-dependent diabetes mellitus caused by rare autosomal-dominant mutations. MODY genes play key biochemical roles in the pancreatic beta cell; therefore, common variants of MODY genes are excellent candidate genes for type 2 diabetes. We review recent studies that suggest that common MODY gene variation contributes modestly to the heritability of type 2 diabetes.

P2 promoter variants of the hepatocyte nuclear factor 4alpha gene are associated with type 2 diabetes in Mexican Americans

Common and rare variants of the hepatocyte nuclear factor 4alpha (HNF4A) gene have been associated with type 2 diabetes and related traits in several populations suggesting the involvement of this transcription factor in diabetes pathogenesis. Single nucleotide polymorphisms (SNPs) within a large haplotype block surrounding the alternate P2 promoter, located approximately 45 kb upstream from the coding region, have been investigated in several populations of varying ethnicity with inconsistent results. Additionally, SNPs located within the P1 promoter and coding region have also been inconsistently associated with type 2 diabetes. Characterization of variation across this gene region in Mexican-American populations has not been reported. We therefore examined polymorphisms across the HNF4A gene in a cohort of Mexican-American pedigrees and assessed their association with type 2 diabetes. We observed evidence for association of SNPs in the P2 promoter region with type 2 diabetes (P = 0.003) and its age at diagnosis (P = 0.003). The risk allele frequency (53%) was intermediate to that reported in Caucasian populations (20-27%) and Pima Indians (83%). No other SNPs were associated with either trait. These results support the possibility that a variant in the P2 promoter region of HNF4A, or variants in linkage disequilibrium within this region, contributes to susceptibility to type 2 diabetes in many ethnic populations including Mexican Americans.

Alternate mRNA processing of the hepatocyte nuclear factor genes and its role in monogenic diabetes

Variation in mRNA processing has the capacity to exert fine control over gene expression in most cell types. The hepatic nuclear factor genes, like approximately 74% of the genome, produce multiple transcripts. Hepatic nuclear factor isoforms exhibit both spatial and temporal variation in expression. In this review, the known isoforms of the hepatocyte nuclear factor-1α, hepatocyte nuclear factor-1β and hepatocyte nuclear factor-4α genes are described and their properties are compared. Finally, data are discussed regarding the influence of hepatocyte nuclear factor-1α alternate mRNA processing on the clinical phenotype of maturity-onset diabetes of the young.

Monogenic diabetes in children and young adults: Challenges for researcher, clinician and patient

Monogenic diabetes results from one or more mutations in a single gene which might hence be rare but has great impact leading to diabetes at a very young age. It has resulted in great challenges for researchers elucidating the aetiology of diabetes and related features in other organ systems, for clinicians specifying a diagnosis that leads to improved genetic counselling, predicting of clinical course and changes in treatment, and for patients to altered treatment that has lead to coming off insulin and injections with no alternative (Glucokinase mutations), insulin injections being replaced by tablets (e.g. low dose in HNFalpha or high dose in potassium channel defects -Kir6.2 and SUR1) or with tablets in addition to insulin (e.g. metformin in insulin resistant syndromes). Genetic testing requires guidance to test for what gene especially given limited resources. Monogenic diabetes should be considered in any diabetic patient who has features inconsistent with their current diagnosis (unspecified neonatal diabetes, type 1 or type 2 diabetes) and clinical features of a specific subtype of monogenic diabetes (neonatal diabetes, familial diabetes, mild hyperglycaemia, syndromes). Guidance is given by clinical and physiological features in patient and family and the likelihood of the proposed mutation altering clinical care. In this article, I aimed to provide insight in the genes and mutations involved in insulin synthesis, secretion, and resistance, and to provide guidance for genetic testing by showing the clinical and physiological features and tests for each specified diagnosis as well as the opportunities for treatment.

A novel -192c/g mutation in the proximal P2 promoter of the hepatocyte nuclear factor-4 alpha gene (HNF4A) associates with late-onset diabetes

Recently, it has been shown that mutations in the P2 promoter of the hepatocyte nuclear factor (HNF)-4 alpha gene (HNF4A) cause maturity-onset diabetes of the young (MODY), while single nucleotide polymorphisms in this locus are associated with type 2 diabetes. In this study, we examined 1,189 bp of the P2 promoter and the associated exon 1D of HNF4A for variations associated with diabetes in 114 patients with type 2 diabetes, 72 MODYX probands, and 85 women with previous gestational diabetes mellitus. A -192c/g mutation was found in five patients. We screened 1,587 diabetic subjects and 4,812 glucose-tolerant subjects for the -192c/g mutation and identified 5 diabetic and 1 glucose-tolerant mutation carriers (P=0.004). Examination of the families showed that carriers of the -192c/g mutation had a significantly impaired glucose-stimulated insulin release and lower levels of serum total cholesterol compared with matched control subjects. Furthermore, the mutation disrupted the binding of an unidentified sequence-specific DNA binding complex present in human islet extracts. Also, two novel linked polymorphisms in the P2 promoter at positions -1107g/t and -858c/t were identified. These variants were not significantly associated with type 2 diabetes or any pre-diabetic traits. In conclusion, a rare, novel mutation that disrupts a protein binding site in the pancreatic HNF4A promoter associates with late-onset diabetes.