Clinical implications of a molecular genetic classification of monogenic beta-cell diabetes

When is it MODY? Challenges in the Interpretation of Sequence Variants in MODY Genes

The genomics revolution has raised more questions than it has provided answers. Big data from large population-scale resequencing studies are increasingly deconstructing classic notions of Mendelian disease genetics, which support a simplistic correlation between mutational severity and phenotypic outcome. The boundaries are being blurred as the body of evidence showing monogenic disease-causing alleles in healthy genomes, and in the genomes of individu-als with increased common complex disease risk, continues to grow. In this review, we focus on the newly emerging challenges which pertain to the interpretation of sequence variants in genes implicated in the pathogenesis of maturity-onset diabetes of the young (MODY), a presumed mono-genic form of diabetes characterized by Mendelian inheritance. These challenges highlight the complexities surrounding the assignments of pathogenicity, in particular to rare protein-alerting variants, and bring to the forefront some profound clinical diagnostic implications. As MODY is both genetically and clinically heterogeneous, an accurate molecular diagnosis and cautious extrapolation of sequence data are critical to effective disease management and treatment. The biological and translational value of sequence information can only be attained by adopting a multitude of confirmatory analyses, which interrogate variant implication in disease from every possible angle. Indeed, studies which have effectively detected rare damaging variants in known MODY genes in normoglycemic individuals question the existence of a sin-gle gene mutation scenario: does monogenic diabetes exist when the genetic culprits of MODY have been systematical-ly identified in individuals without MODY?

Xenopus as a model system for studying pancreatic development and diabetes

Diabetes is a chronic disease caused by the loss or dysfunction of the insulin-producing β-cells in the pancreas. To date, much of our knowledge about β-cells in humans comes from studying rare monogenic forms of diabetes. Importantly, the majority of mutations so far associated to monogenic diabetes are in genes that exert a regulatory role in pancreatic development and/or β-cell function. Thus, the identification and study of novel mutations open an unprecedented window into human pancreatic development. In this review, we summarize major advances in the genetic dissection of different types of monogenic diabetes and the insights gained from a developmental perspective. We highlight future challenges to bridge the gap between the fast accumulation of genetic data through next-generation sequencing and the need of functional insights into disease mechanisms. Lastly, we discuss the relevance and advantages of studying candidate gene variants in vivo using the Xenopus as model system.

Development and stability study of glibenclamide oral liquid paediatric formulations for the treatment of permanent neonatal diabetes mellitus

Background

Glibenclamide is a second-generation oral sulfonylurea used to treat neonatal permanent diabetes mellitus. It is more effective and safer than the first-generation agents. However, no liquid oral formulation is commercially available and, therefore, it cannot be used for individuals who cannot swallow the solid form.

Objectives

To develop and study the physicochemical and microbiological stability of two liquid glibenclamide formulations for the treatment of permanent neonatal diabetes mellitus: two suspensions (2.5 mg/mL)-one using glibenclamide raw material and the other, glibenclamide tablets. Furthermore, high-performance liquid chromatography (HPLC) stability showed that the method is optimised and validated for analysis of glibenclamide in the formulations studied.

Methods

Samples were stored at 4°C, 25°C and 40°C. The amount of glibenclamide in each formulation was analysed in duplicate using HPLC at 0, 7, 14, 28, 60 and 90 days. Other parameters were also determined-for example, the appearance, pH and morphology. Microbiological studies according to the guidelines of the US Pharmacopoeia for non-sterile products at 0 and 90 days were carried out.

Results

All formulations remained physicochemically and microbiologically stable at three different temperatures during the 90-day study. Therefore, glibenclamide formulations can be stored for at least 90 days at ≤40°C.

Conclusions

These formulations are ideally suited for paediatric patients who usually cannot swallow tablets. The proposed analytical method was suitable for studying the stability of different formulations.

The past 10 years-new hormones, new functions, new endocrine organs

Since the publication of the first issue of this journal in November 2005, our understanding of the endocrine system has evolved, with the identification of novel hormones and novel endocrine roles for previously identified molecules. Here, we have asked six of our Advisory Board Members to comment on how these insights have led to the recognition that many organs and tissues that were not widely considered part of the classic endocrine system in the past have important endocrine functions.

A genetic diagnosis of maturity-onset diabetes of the young (MODY): experiences of patients and family members

AIMS

Genetic testing for maturity-onset diabetes of the young (MODY) facilitates a correct diagnosis, enabling treatment optimization and allowing monitoring of asymptomatic family members. To date, the majority of people with MODY remain undiagnosed. To identify patients' needs and areas for improving care, this study explores the experiences of patients and family members who have been genetically tested for MODY.

METHODS

Fourteen semi-structured interviews with patients and the parents of patients, and symptomatic and asymptomatic family members were conducted. Atlas.ti was used for thematic analysis.

RESULTS

Most people with MODY were initially misdiagnosed with Type 1 or Type 2 diabetes; they had been seeking for the correct diagnosis for a long time. Reasons for having a genetic test included reassurance, removing the uncertainty of developing diabetes (in asymptomatic family members) and informing relatives. Reasons against testing were the fear of genetic discrimination and not having symptoms. Often a positive genetic test result did not come as a surprise. Both patients and family members were satisfied with the decision to get tested because it enabled them to adjust their lifestyle and treatment accordingly. All participants experienced a lack of knowledge of MODY among healthcare professionals, in their social environment and in patient organizations. Additionally, problems with the reimbursement of medical expenses were reported.

CONCLUSIONS

Patients and family members are generally positive about genetic testing for MODY. More education of healthcare professionals and attention on the part of diabetes organizations is needed to increase awareness and optimize care and support for people with MODY.

New insights from monogenic diabetes for "common" type 2 diabetes

Boundaries between monogenic and complex genetic diseases are becoming increasingly blurred, as a result of better understanding of phenotypes and their genetic determinants. This had a large impact on the way complex disease genetics is now being investigated. Starting with conventional approaches like familial linkage, positional cloning and candidate genes strategies, the scope of complex disease genetics has grown exponentially with scientific and technological advances in recent times. Despite identification of multiple loci harboring common and rare variants associated with complex diseases, interpreting and evaluating their functional role has proven to be difficult. Information from monogenic diseases, especially related to the intermediate traits associated with complex diseases comes handy. The significant overlap between traits and phenotypes of monogenic diseases with related complex diseases provides a platform to understand the disease biology better. In this review, we would discuss about one such complex disease, type 2 diabetes, which shares marked similarity of intermediate traits with different forms of monogenic diabetes.

Postprandial incretin and islet hormone responses and dipeptidyl-peptidase 4 enzymatic activity in patients with maturity onset diabetes of the young

OBJECTIVE

The role of the incretin hormones in the pathophysiology of maturity onset diabetes of the young (MODY) is unclear.

DESIGN

We studied the postprandial plasma responses of glucagon, incretin hormones (glucagon-like peptide 1 (GLP1) and glucose-dependent insulinotropic polypeptide (GIP)) and dipeptidyl-peptidase 4 (DPP4) enzymatic activity in patients with glucokinase (GCK) diabetes (MODY2) and hepatocyte nuclear factor 1α (HNF1A) diabetes (MODY3) as well as in matched healthy individuals (CTRLs).

SUBJECTS AND METHODS

Ten patients with MODY2 (mean age ± S.E.M. 43 ± 5 years; BMI 24 ± 2 kg/m(2); fasting plasma glucose (FPG) 7.1 ± 0.3 mmol/l: HbA1c 6.6 ± 0.2%), ten patients with MODY3 (age 31 ± 3 years; BMI 24 ± 1 kg/m(2); FPG 8.9 ± 0.8 mmol/l; HbA1c 7.0 ± 0.3%) and ten CTRLs (age 40 ± 5 years; BMI 24 ± 1 kg/m(2); FPG 5.1 ± 0.1 mmol/l; HbA1c 5.3 ± 0.1%) were examined with a liquid test meal.

RESULTS

All of the groups exhibited similar baseline values of glucagon (MODY2: 7 ± 1 pmol/l; MODY3: 6 ± 1 pmol/l; CTRLs: 8 ± 2 pmol/l, P=0.787), but patients with MODY3 exhibited postprandial hyperglucagonaemia (area under the curve (AUC) 838 ± 108 min × pmol/l) as compared to CTRLs (182 ± 176 min × pmol/l, P=0.005) and tended to have a greater response than did patients with MODY2 (410 ± 154 min × pmol/l, P=0.063). Similar peak concentrations and AUCs for plasma GIP and plasma GLP1 were observed across the groups. Increased fasting DPP4 activity was seen in patients with MODY3 (17.7 ± 1.2 mU/ml) vs CTRLs (13.6 ± 0.8 mU/ml, P=0.011), but the amount of activity was similar to that in patients with MODY2 (15.0 ± 0.7 mU/ml, P=0.133).

CONCLUSION

The pathophysiology of MODY3 includes exaggerated postprandial glucagon responses and increased fasting DPP4 enzymatic activity but normal postprandial incretin responses both in patients with MODY2 and in patients with MODY3.

A novel nonsense mutation of the HNF1α in maturity-onset diabetes of the young type 3 in Asian population

We reported a novel nonsense mutation, R54X of the hepatic nuclear factor 1α (HNF1α) gene in a Chinese family. The mutation was identified in a 47 years old woman and her 19 years old daughter within a five-family members tested. Both the two patients were sensitive to insulin and glibenclamide treatments.

Recognition and Management of Individuals With Hyperglycemia Because of a Heterozygous Glucokinase Mutation

Glucokinase-maturity-onset diabetes of the young (GCK-MODY), also known as MODY2, is caused by heterozygous inactivating mutations in the GCK gene. GCK gene mutations are present in ∼1 in 1,000 of the population, but most are not diagnosed. They are common causes of MODY (10-60%): persistent incidental childhood hyperglycemia (10-60%) and gestational diabetes mellitus (1-2%). GCK-MODY has a unique pathophysiology and clinical characteristics, so it is best considered as a discrete genetic subgroup. People with GCK-MODY have a defect in glucose sensing; hence, glucose homeostasis is maintained at a higher set point resulting in mild, asymptomatic fasting hyperglycemia (5.4-8.3 mmol/L, HbA1c range 5.8-7.6% [40-60 mmol/mol]), which is present from birth and shows slight deterioration with age. Even after 50 years of mild hyperglycemia, people with GCK-MODY do not develop significant microvascular complications, and the prevalence of macrovascular complications is probably similar to that in the general population. Treatment is not recommended outside pregnancy because glucose-lowering therapy is ineffective in people with GCK-MODY and there is a lack of long-term complications. In pregnancy, fetal growth is primarily determined by whether the fetus inherits the GCK gene mutation from their mother. Insulin treatment of the mother is only appropriate when increased fetal abdominal growth on scanning suggests the fetus is unaffected. The impact on outcome of maternal insulin treatment is limited owing to the difficulty in altering maternal glycemia in these patients. Making the diagnosis of GCK-MODY through genetic testing is essential to avoid unnecessary treatment and investigations, especially when patients are misdiagnosed with type 1 or type 2 diabetes.

Monogenic diabetes and pregnancy

Monogenic diabetes is frequently mistakenly diagnosed as either type 1 or type 2 diabetes, yet accounts for approximately 1-2% of diabetes. Identifying monogenic forms of diabetes has practical implications for specific therapy, screening of family members and genetic counselling. The most common forms of monogenic diabetes are due to glucokinase (GCK), hepatocyte nuclear factor (HNF)-1A and HNF-4A, HNF-1B, m.3243A>G gene defects. Practical aspects of their recognition, diagnosis and management are outlined, particularly as they relate to pregnancy. This knowledge is important for all physicians managing diabetes in pregnancy, given this is a time when previously unrecognised monogenic diabetes may be uncovered with careful attention to atypical features of diabetes misclassified as type 1, type 2, or gestational diabetes.

Diabetes mellitus: The epidemic of the century

The epidemic nature of diabetes mellitus in different regions is reviewed. The Middle East and North Africa region has the highest prevalence of diabetes in adults (10.9%) whereas, the Western Pacific region has the highest number of adults diagnosed with diabetes and has countries with the highest prevalence of diabetes (37.5%). Different classes of diabetes mellitus, type 1, type 2, gestational diabetes and other types of diabetes mellitus are compared in terms of diagnostic criteria, etiology and genetics. The molecular genetics of diabetes received extensive attention in recent years by many prominent investigators and research groups in the biomedical field. A large array of mutations and single nucleotide polymorphisms in genes that play a role in the various steps and pathways involved in glucose metabolism and the development, control and function of pancreatic cells at various levels are reviewed. The major advances in the molecular understanding of diabetes in relation to the different types of diabetes in comparison to the previous understanding in this field are briefly reviewed here. Despite the accumulation of extensive data at the molecular and cellular levels, the mechanism of diabetes development and complications are still not fully understood. Definitely, more extensive research is needed in this field that will eventually reflect on the ultimate objective to improve diagnoses, therapy and minimize the chance of chronic complications development.

Identifying monogenic diabetes in a pediatric cohort with presumed type 1 diabetes

OBJECTIVE

Monogenic diabetes (MD) is rare and can often be confused with type 1 diabetes (T1D) in a pediatric cohort. We sought to determine clinical criteria that could optimally identify candidates for genetic testing of two common forms of MD that alter therapy: glucokinase (GCK) and hepatocyte nuclear factor 1 alpha (HNF1α).

RESEARCH DESIGN AND METHODS

We performed a retrospective chart review of 939 patients with a presumed diagnosis of T1D, 6 months-20 yr of age, and identified four clinical criteria that were unusual for T1D and could warrant further evaluation for MD: (i) negative pancreatic autoantibodies, (ii) evidence of prolonged endogenous insulin production, or (iii) strong family history of diabetes in multiple generations. One hundred and twenty-one patients were identified as having one or more of these high-risk clinical criteria and were offered screening for mutations in GCK and HNF1α; 58 consented for genetic testing.

RESULTS

Of 58 patients with presumed T1D who underwent genetic testing, four were found to have GCK and one had HNF1α. No patients with only one high-risk feature were found to have MD. Of 10 patients who had two or more high risk criteria, five had MD (50%).

CONCLUSION

A high frequency of MD from mutations in GCK/HNF1α may be identified among pediatric diabetic patients originally considered to have T1D by performing genetic testing on those patients with multiple clinical risk factors for MD.

Diabetic ketoacidosis in the setting of HNF1A-maturity onset diabetes of the young

A female patient was treated for type 1 diabetes following presentation at 12 years of age with hyperglycaemia, polydipsia and weight loss. Eleven years later, while screening relatives attending a genetic diabetes clinic, she was identified as potentially harbouring a mutation in the hepatocyte nuclear factor 1A (HNF1A) gene. Biochemical testing supported the diagnosis of HNF1A-maturity onset diabetes of the young (MODY) and genetic screening was positive for a heterozygous mutation in the HNF1A gene. The patient transitioned from insulin to sulfonylurea therapy. Three years later, in the setting of poor metabolic control, the patient presented to the emergency department with a history of nausea, vomiting and palpitations. A diagnosis of diabetic ketoacidosis (DKA) was confirmed and successfully treated. Although a diagnosis of HNF1A-MODY is rarely considered in a patient with a history of DKA, we demonstrate that DKA is possible in the setting of non-compliance with sulfonylurea therapy.

Genetics of type 2 diabetes-pitfalls and possibilities

Type 2 diabetes (T2D) is a complex disease that is caused by a complex interplay between genetic, epigenetic and environmental factors. While the major environmental factors, diet and activity level, are well known, identification of the genetic factors has been a challenge. However, recent years have seen an explosion of genetic variants in risk and protection of T2D due to the technical development that has allowed genome-wide association studies and next-generation sequencing. Today, more than 120 variants have been convincingly replicated for association with T2D and many more with diabetes-related traits. Still, these variants only explain a small proportion of the total heritability of T2D. In this review, we address the possibilities to elucidate the genetic landscape of T2D as well as discuss pitfalls with current strategies to identify the elusive unknown heritability including the possibility that our definition of diabetes and its subgroups is imprecise and thereby makes the identification of genetic causes difficult.

Molecular genetic testing of patients with monogenic diabetes and hyperinsulinism

Genetic sequencing has become a critical part of the diagnosis of certain forms of pancreatic beta cell dysfunction. Despite great advances in the speed and cost of DNA sequencing, determining the pathogenicity of variants remains a challenge, and requires sharing of sequence and phenotypic data between laboratories. We reviewed all diabetes and hyperinsulinism-associated molecular testing done at the Seattle Children's Molecular Genetics Laboratory from 2009 to 2013. 331 probands were referred to us for molecular genetic sequencing for Neonatal Diabetes (NDM), Maturity-Onset Diabetes of the Young (MODY), or Congenital Hyperinsulinism (CHI) during this period. Reportable variants were identified in 115 (35%) patients with 91 variants in one of 6 genes: HNF1A, GCK, HNF4A, ABCC8, KCNJ11, or INS. In addition to identifying 23 novel variants, we identified unusual mechanisms of inheritance, including mosaic and digenic MODY presentations. Re-analysis of all reported variants using more recently available databases led to a change in variant interpretation from the original report in 30% of cases. These results represent a resource for molecular testing of monogenic forms of diabetes and hyperinsulinism, providing a mutation spectrum for these disorders in a large North American cohort. In addition, they highlight the importance of periodic review of molecular testing results.

A novel mutation of the HNF1B gene associated with hypoplastic glomerulocystic kidney disease and neonatal renal failure: a case report and mutation update

Hepatocyte nuclear factor 1 beta (HNF1B) plays an important role in embryonic development, namely in the kidney, pancreas, liver, genital tract, and gut. Heterozygous germline mutations of HNF1B are associated with the renal cysts and diabetes syndrome (RCAD). Affected individuals may present a variety of renal developmental abnormalities and/or maturity-onset diabetes of the young (MODY). A Portuguese 19-month-old male infant was evaluated due to hypoplastic glomerulocystic kidney disease and renal dysfunction diagnosed in the neonatal period that progressed to stage 5 chronic renal disease during the first year of life. His mother was diagnosed with a solitary hypoplastic microcystic left kidney at age 20, with stage 2 chronic renal disease established at age 35, and presented bicornuate uterus, pancreatic atrophy, and gestational diabetes. DNA sequence analysis of HNF1B revealed a novel germline frameshift insertion (c.110_111insC or c.110dupC) in both the child and the mother. A review of the literature revealed a total of 106 different HNF1B mutations, in 236 mutation-positive families, comprising gross deletions (34%), missense mutations (31%), frameshift deletions or insertions (15%), nonsense mutations (11%), and splice-site mutations (8%). The study of this family with an unusual presentation of hypoplastic glomerulocystic kidney disease with neonatal renal dysfunction identified a previously unreported mutation of the HNF1B gene, thereby expanding the spectrum of known mutations associated with renal developmental disorders.

Absence of BiP co-chaperone DNAJC3 causes diabetes mellitus and multisystemic neurodegeneration

Diabetes mellitus and neurodegeneration are common diseases for which shared genetic factors are still only partly known. Here, we show that loss of the BiP (immunoglobulin heavy-chain binding protein) co-chaperone DNAJC3 leads to diabetes mellitus and widespread neurodegeneration. We investigated three siblings with juvenile-onset diabetes and central and peripheral neurodegeneration, including ataxia, upper-motor-neuron damage, peripheral neuropathy, hearing loss, and cerebral atrophy. Exome sequencing identified a homozygous stop mutation in DNAJC3. Screening of a diabetes database with 226,194 individuals yielded eight phenotypically similar individuals and one family carrying a homozygous DNAJC3 deletion. DNAJC3 was absent in fibroblasts from all affected subjects in both families. To delineate the phenotypic and mutational spectrum and the genetic variability of DNAJC3, we analyzed 8,603 exomes, including 506 from families affected by diabetes, ataxia, upper-motor-neuron damage, peripheral neuropathy, or hearing loss. This analysis revealed only one further loss-of-function allele in DNAJC3 and no further associations in subjects with only a subset of the features of the main phenotype. Our findings demonstrate that loss-of-function DNAJC3 mutations lead to a monogenic, recessive form of diabetes mellitus in humans. Moreover, they present a common denominator for diabetes and widespread neurodegeneration. This complements findings from mice in which knockout of Dnajc3 leads to diabetes and modifies disease in a neurodegenerative model of Marinesco-Sjögren syndrome.

Treatment of transient neonatal diabetes mellitus: insulin pump or insulin glargine? Our experience

Neonatal diabetes mellitus (NDM) results from impaired insulin secretion, occurring within the first 6 months of life. NDM is classified as transient NDM (TNDM) or permanent NDM. To date there are no universal guidelines regarding its management. Intravenous insulin infusion represents the first and most adequate therapeutic approach for sustained hyperglycemia, but this can provide only a short-term solution. Several factors should be taken into account in the choice of the long-term treatment. We describe our experience with two infants affected by TNDM. The first child was treated with continuous subcutaneous insulin infusion, whereas the second infant was treated with subcutaneous insulin glargine injections. Our experience shows that the two different therapeutic approaches, if properly managed, are equally effective.

Fetal macrosomia and neonatal hyperinsulinemic hypoglycemia associated with transplacental transfer of sulfonylurea in a mother with KCNJ11-related neonatal diabetes

OBJECTIVE

Sulfonylureas (SUs) are effective at controlling glycemia in permanent neonatal diabetes mellitus (PNDM) caused by KCNJ11 (Kir6.2) mutations.

RESEARCH DESIGN AND METHODS

We report the case of a woman with PNDM who continued high doses of glibenclamide (85 mg/day) during her pregnancy. The baby was born preterm, and presented with macrosomia and severe hyperinsulinemic hypoglycemia requiring high-rate intravenous glucose infusion.

RESULTS

Postnatal genetic testing excluded a KCNJ11 mutation in the baby. Glibenclamide was detected in both the baby's blood and the maternal milk.

CONCLUSIONS

We hypothesize that high doses of glibenclamide in the mother led to transplacental passage of the drug and overstimulation of fetal β-cells, which resulted in severe hyperinsulinemic hypoglycemia in the neonate (who did not carry the mutation) and contributed to fetal macrosomia. We suggest that glibenclamide (and other SUs) should be avoided in mothers with PNDM if the baby does not carry the mutation or if prenatal screening has not been performed, while glibenclamide may be beneficial when the fetus is a PNDM carrier.

Phenotypic heterogeneity in monogenic diabetes: the clinical and diagnostic utility of a gene panel-based next-generation sequencing approach

Single gene mutations that primarily affect pancreatic β-cell function account for approximately 1-2% of all cases of diabetes. Overlapping clinical features with common forms of diabetes makes diagnosis of monogenic diabetes challenging. A genetic diagnosis often leads to significant alterations in treatment, allows better prediction of disease prognosis and progression, and has implications for family members. Currently, genetic testing for monogenic diabetes relies on selection of appropriate individual genes for analysis based on the availability of often-limited phenotypic information, decreasing the likelihood of making a genetic diagnosis. We thus developed a targeted next-generation sequencing (NGS) assay for the detection of mutations in 36 genes known to cause monogenic forms of diabetes, including transient or permanent neonatal diabetes mellitus (TNDM or PNDM), maturity-onset diabetes of the young (MODY) and rare syndromic forms of diabetes. A total of 95 patient samples were analyzed: 19 with known causal mutations and 76 with a clinically suggestive phenotype but lacking a genetic diagnosis. All previously identified mutations were detected, validating our assay. Pathogenic sequence changes were identified in 19 out of 76 (25%) patients: 7 of 32 (22%) NDM cases, and 12 of 44 (27%) MODY cases. In 2 NDM patients the causal mutation was not expected as consanguinity was not reported and there were no clinical features aside from diabetes. A 3 year old patient with NDM diagnosed at 3 months of age, who previously tested negative for INS, KCNJ11 and ABCC8 mutations, was found to carry a novel homozygous mutation in EIF2AK3 (associated with Wolcott-Rallison syndrome), a gene not previously suspected because consanguinity, delayed growth, abnormal bone development and hepatic complications had not been reported. Similarly, another infant without a history of consanguinity was found to have a homozygous GCK mutation causing PNDM at birth. This study demonstrates the effectiveness of multi-gene panel analysis in uncovering molecular diagnoses in patients with monogenic forms of diabetes.

Early-onset type 2 diabetes mellitus is associated to HNF4A T130I polymorphism in families of central Spain

PURPOSE

Type 2 diabetes mellitus (type 2 DM) and maturity-onset diabetes of the young present some similar clinical and biochemical characteristics that make them difficult to differentiate. Currently, the polymorphism T130I (rs1800961) in the HNF4A (hepatocyte nuclear factor 4A) gene has been described as a risk factor to type 2 DM and shows an autosomal dominant inheritance pattern associated to β-cell function decrease. The aim of the present work was to characterize the phenotypic profile of the T130I carrier and noncarrier relatives included in 3 unrelated families.

METHODS

We studied GCK, HNF1A, and HNF4A genes by polymerase chain reaction and sequencing in 3 unrelated subjects from Valladolid, Spain, in which maturity-onset diabetes of the young was suspected. We collected genetic, clinical, and biochemical data from these subjects and their relatives in order to check the presence of the T130I polymorphism.

RESULTS

The heterozygous T130I mutation was the unique functional gene variation that could explain diabetes phenotype. We observed significant differences in glucose metabolism, lipid profile, and Homeostasis Model Assessment index when we compared T130I mutation carriers and noncarriers. Diabetes diagnosed in T130I mutation carriers was related to stressful situations in an earlier age and tightly associated with gestational diabetes. Fasting plasma glucose and HbA(1c) levels increased with age in all carriers (r = 0.69 and r = 0.66, P < 0.01), respectively.

CONCLUSIONS

Our study supports the T130I variant in HNF4A as a major susceptibility genotype associated with early-onset type 2 DM. Healthy carriers of this mutation require a stricter control in the population of central Spain.

Molecular and clinical characterization of glucokinase maturity-onset diabetes of the young (GCK-MODY) in Japanese patients

AIMS

To investigate the molecular and clinical characteristics of the largest series of Japanese patients with glucokinase maturity-onset diabetes of the young (GCK-MODY), and to find any features specific to Asian people.

METHODS

We enrolled 78 Japanese patients with GCK-MODY from 41 families (55 probands diagnosed at the age of 0-14 years and their 23 adult family members). Mutations were identified by direct sequencing or multiplex ligation-dependent probe amplification of all exons of the GCK gene. Detailed clinical and laboratory data were collected on the probands using questionnaires, which were sent to the treating physicians.　Data on current clinical status and HbA1c levels were also collected from adult patients.

RESULTS

A total of 35 different mutations were identified, of which seven were novel. Fasting blood glucose and HbA1c levels of the probands were ≤9.3 mmol/l and ≤56 mmol/mol (7.3%), respectively, and there was considerable variation in their BMI percentiles (0.4-96.2). In total, 25% of the probands had elevated homeostatic assessment of insulin resistance values, and 58.3% of these had evidence of concomitant Type 2 diabetes in their family. The HbA1c levels for adults were slightly higher, up to 61 mmol/mol (7.8%). The incidence of microvascular complications was low. Out of these 78 people with GCK-MODY and 40 additional family members with hyperglycaemia whose genetic status was unknown, only one had diabetic nephropathy.

CONCLUSIONS

The molecular and clinical features of GCK-MODY in Japanese people are similar to those of other ethnic populations; however, making a diagnosis of GCK-MODY was more challenging in patients with signs of insulin resistance.

Current and best practices of genetic testing for maturity onset diabetes of the young: views of professional experts

AIMS

Currently, many patients with maturity onset diabetes of the young (MODY) are undiagnosed or misdiagnosed with type 1 or 2 diabetes. This study aims to assess professional experts' views on factors which may influence the current practice of genetic testing for MODY and to explore next steps toward best practice.

METHODS

Twelve semistructured interviews were conducted with professional experts. These experts included physicians with potential or actual experience with genetic testing for MODY, representatives of (para)medical professional associations and a staff member of a diabetes patients' organization.

RESULTS

Participants differed in their valuation of genetic testing for MODY. While most considered the test useful, not all were convinced of its clinical utility. Other factors mentioned to influence current practice were: (perceived lack of) possibilities for treatment and prevention, patients' perspectives and perceived barriers, such as costs and a lack of knowledge and awareness. Participants agreed that guidelines would be helpful to facilitate expedient testing.

CONCLUSIONS

This study identified next steps that should be taken to improve genetic diagnosis and care for patients with MODY. Besides the development of a consensus guideline, other suggestions included more education of healthcare professionals, a clearer allocation of responsibilities with regard to genetic testing for MODY and further research.

An integrated cell purification and genomics strategy reveals multiple regulators of pancreas development

The regulatory logic underlying global transcriptional programs controlling development of visceral organs like the pancreas remains undiscovered. Here, we profiled gene expression in 12 purified populations of fetal and adult pancreatic epithelial cells representing crucial progenitor cell subsets, and their endocrine or exocrine progeny. Using probabilistic models to decode the general programs organizing gene expression, we identified co-expressed gene sets in cell subsets that revealed patterns and processes governing progenitor cell development, lineage specification, and endocrine cell maturation. Purification of Neurog3 mutant cells and module network analysis linked established regulators such as Neurog3 to unrecognized gene targets and roles in pancreas development. Iterative module network analysis nominated and prioritized transcriptional regulators, including diabetes risk genes. Functional validation of a subset of candidate regulators with corresponding mutant mice revealed that the transcription factors Etv1, Prdm16, Runx1t1 and Bcl11a are essential for pancreas development. Our integrated approach provides a unique framework for identifying regulatory genes and functional gene sets underlying pancreas development and associated diseases such as diabetes mellitus.

Discovery of specific pancreas developmental regulators has accelerated in recent years. In contrast, the global regulatory programs controlling pancreas development are poorly understood compared to other organs or tissues like heart or blood. Decoding this regulatory logic may accelerate development of replacement organs from renewable sources like stem cells, but this goal requires identification of regulators and assessment of their functions on a global scale. To address this important challenge for pancreas biology, we combined purification of normal and mutant cells with genome-scale methods to generate and analyze expression profiles from developing pancreas cells. Our work revealed regulatory gene sets governing development of pancreas progenitor cells and their progeny. Our integrative approach nominated multiple pancreas developmental regulators, including suspected risk genes for human diabetes, which we validated by phenotyping mutant mice on a scale not previously reported. Selection of these candidate regulators was unbiased; thus it is remarkable that all were essential for pancreatic islet development. Thus, our studies provide a new heuristic resource for identifying genetic functions underlying pancreas development and diseases like diabetes mellitus.

Incretin effect and glucagon responses to oral and intravenous glucose in patients with maturity-onset diabetes of the young--type 2 and type 3

Maturity-onset diabetes of the young (MODY) is a clinically and genetically heterogeneous subgroup of nonautoimmune diabetes, constituting 1-2% of all diabetes. Because little is known about incretin function in patients with MODY, we studied the incretin effect and hormone responses to oral and intravenous glucose loads in patients with glucokinase (GCK)-diabetes (MODY2) and hepatocyte nuclear factor 1α (HNF1A)-diabetes (MODY3), respectively, and in matched healthy control subjects. Both MODY groups exhibited glucose intolerance after oral glucose (most pronounced in patients with HNF1A-diabetes), but only patients with HNF1A-diabetes had impaired incretin effect and inappropriate glucagon responses to OGTT. Both groups of patients with diabetes showed normal suppression of glucagon in response to intravenous glucose. Thus, HNF1A-diabetes, similar to type 2 diabetes, is characterized by an impaired incretin effect and inappropriate glucagon responses, whereas incretin effect and glucagon response to oral glucose remain unaffected in GCK-diabetes, reflecting important pathogenetic differences between the two MODY forms.

Islet cell antibodies (ICA) identify autoimmunity in children with new onset diabetes mellitus negative for other islet cell antibodies

AIMS

The aim of this study was to explore whether islet cell antibodies (ICA) could be identified in children with newly onset diabetes mellitus but negative for autoantibodies against glutamic acid decarboxylase (GADA), islet antigen-2 (IA-2A), insulin (IAA), or any of the three variants with arginine (R), tryptophan (W), or glutamine (Q) at position 325 of the zinc transporter 8 (ZnT8A).

METHODS

A population-based analysis of autoantibodies was performed from 1 May 2005 to 2 September 2010 in Swedish children newly diagnosed with diabetes. ICA was analyzed with an enzyme-linked immunosorbent assay and if positive, reanalyzed in the classical ICA immunofluorescence assay, in 341 samples among 3545 children who had been tested negative for all of GADA, IA-2A, IAA, or ZnT8A (R, W, Q).

RESULTS

An isolated positivity for ICA was identified in 5.0% (17/341) of the newly diagnosed children. The levels of ICA in positive subjects ranged from 3 to 183 JDF-U (median 30). This finding increased the diagnostic sensitivity of islet autoimmunity as 3204/3545 patients (90.4%) were islet autoantibody positive without the ICA analyses and 3221 patients (90.9%) were positive with the inclusion of ICA.

CONCLUSIONS

The finding of an isolated positivity for ICA despite negativity for GADA, IA-2A, IAA, and ZnT8A (R, W, Q) suggests that still another yet unidentified autoantigen(s) may contribute to the ICA immunofluorescence. Hence, ICA is important to analyze in type 1 diabetes children and adolescents that would otherwise be islet autoantibody negative.

Genetic Counseling for Diabetes Mellitus

Most diabetes is polygenic in etiology, with (type 1 diabetes, T1DM) or without (type 2 diabetes, T2DM) an autoimmune basis. Genetic counseling for diabetes generally focuses on providing empiric risk information based on family history and/or the effects of maternal hyperglycemia on pregnancy outcome. An estimated one to five percent of diabetes is monogenic in nature, e.g., maturity onset diabetes of the young (MODY), with molecular testing and etiology-based treatment available. However, recent studies show that most monogenic diabetes is misdiagnosed as T1DM or T2DM. While efforts are underway to increase the rate of diagnosis in the diabetes clinic, genetic counselors and clinical geneticists are in a prime position to identify monogenic cases through targeted questions during a family history combined with working in conjunction with diabetes professionals to diagnose and assure proper treatment and familial risk assessment for individuals with monogenic diabetes.

Clinical and molecular characterization of maturity onset-diabetes of the young caused by hepatocyte nuclear factor-4 alpha mutation: red flags for prediction of the diagnosis

BACKGROUND AND OBJECTIVES

The prevalence of maturity-onset diabetes of the young (MODY) in Saudi population remains unknown, and data on molecular etiology of this condition is limited. Therefore, the present study was undertaken to elucidate clinical and molecular characteristics of a Saudi family with MODY 1.

DESIGN AND SETTINGS

This is a case series study conducted at Saad Specialist Hospital in Alkhobar, Saudi Arabia.

PATIENTS AND METHODS

A 12-year-old female presented to us with symptoms suggestive of diabetes. Investigations revealed hyperglycemia, glycosuria, and ketonuria without acidosis. Pancreatic antibodies were negative. She responded well to subcutaneous insulin. Her family history revealed that 2 of her siblings were diagnosed with type 1 diabetes (T1DM), while her father and mother had type 2 diabetes (T2DM). In view of this strong family history, the possibility of monogenic diabetes was raised, and the 2 genes consistent with this phenotype, hepatocyte nuclear factor-1 alpha (HNF1a) and hepatocyte nuclear factor-4 alpha (HNF4a), were studied. Accordingly, genomic DNA was isolated from peripheral blood lymphocytes of the 8 members of this family, polymerase chain reaction was carried out, and sequencing of the whole HNF4a and HNF1a genes was done.

RESULTS

DNA study of the proband revealed a heterozygous substitution in intron 1 (IVS1b C > T-5)(c.50-5C > T) of the HNF1a gene. This mutation was identified in other 5 members of the family.

CONCLUSION

This study alerts physicians to suspect MODY in patients who have a strongly positive family history of diabetes over a few generations with negative pancreatic antibodies and absence of ketoacidosis and obesity.

A decade of molecular genetic testing for MODY: a retrospective study of utilization in The Netherlands

Genetic testing for maturity-onset diabetes of the young (MODY) may be relevant for treatment and prognosis in patients with usually early-onset, non-ketotic, insulin-sensitive diabetes and for monitoring strategies in non-diabetic mutation carriers. This study describes the first 10 years of genetic testing for MODY in The Netherlands in terms of volume and test positive rate, medical setting, purpose of the test and age of patients tested. Some analyses focus on the most prevalent subtype, HNF1A MODY. Data were retrospectively extracted from a laboratory database. In total, 502 individuals were identified with a pathogenic mutation in HNF4A, GCK or HNF1A between 2001 and 2010. Although mutation scanning for MODY was used at an increasing rate, cascade testing was only used for one relative, on average, per positive index patient. Testing for HNF1A MODY was mostly requested by internists and paediatricians, often from regional hospitals. Primary care physicians and clinical geneticists rarely requested genetic testing for HNF1A MODY. Clinical geneticists requested cascade testing relatively more often than other health professionals. A substantial proportion (currently 29%) of HNF1A MODY probands was at least 40 years old at the time of testing. In conclusion, the number of individuals genetically tested for MODY so far in The Netherlands is low compared with previously predicted numbers of patients. Doctors' valuation of the test and patients' and family members' response to (an offer of) genetic testing on the other hand need to be investigated. Efforts may be needed to develop and implement translational guidelines.

The many faces of diabetes: a disease with increasing heterogeneity

Diabetes is a much more heterogeneous disease than the present subdivision into types 1 and 2 assumes; type 1 and type 2 diabetes probably represent extremes on a range of diabetic disorders. Both type 1 and type 2 diabetes seem to result from a collision between genes and environment. Although genetic predisposition establishes susceptibility, rapid changes in the environment (ie, lifestyle factors) are the most probable explanation for the increase in incidence of both forms of diabetes. Many patients have genetic predispositions to both forms of diabetes, resulting in hybrid forms of diabetes (eg, latent autoimmune diabetes in adults). Obesity is a strong modifier of diabetes risk, and can account for not only a large proportion of the epidemic of type 2 diabetes in Asia but also the ever-increasing number of adolescents with type 2 diabetes. With improved characterisation of patients with diabetes, the range of diabetic subgroups will become even more diverse in the future.

Clinical utility of next-generation sequencing for the molecular diagnosis of monogenic diabetes

Monogenic diabetes resulting from mutations that primarily reduce insulin-secreting pancreatic β-cell function accounts for 1-2% of all cases of diabetes, and is genetically and clinically heterogeneous. Currently, genetic testing for monogenic diabetes relies on selection of the appropriate gene for analysis based on the availability of comprehensive phenotypic information, which can be time consuming, costly and can limit the differential diagnosis to a few selected genes. In recent years, the exponential growth in the field of high-throughput capture and sequencing technology has made it possible and cost effective to sequence many genes simultaneously, making it an efficient diagnostic tool for clinically and genetically heterogeneous disorders such as monogenic diabetes. Making a diagnosis of monogenic diabetes is important as it enables more appropriate treatment, better prediction of disease prognosis and progression, and counseling and screening of family members. We provide a concise overview of the genetic etiology of some forms of monogenic diabetes, as well as a discussion of the clinical utility of genetic testing by comprehensive multigene panel using next-generation sequencing methodologies.

Evaluation of a target region capture sequencing platform using monogenic diabetes as a study-model

BACKGROUND

Monogenic diabetes is a genetic disease often caused by mutations in genes involved in beta-cell function. Correct sub-categorization of the disease is a prerequisite for appropriate treatment and genetic counseling. Target-region capture sequencing is a combination of genomic region enrichment and next generation sequencing which might be used as an efficient way to diagnose various genetic disorders. We aimed to develop a target-region capture sequencing platform to screen 117 selected candidate genes involved in metabolism for mutations and to evaluate its performance using monogenic diabetes as a study-model.

RESULTS

The performance of the assay was evaluated in 70 patients carrying known disease causing mutations previously identified in HNF4A, GCK, HNF1A, HNF1B, INS, or KCNJ11. Target regions with a less than 20-fold sequencing depth were either introns or UTRs. When only considering translated regions, the coverage was 100% with a 50-fold minimum depth. Among the 70 analyzed samples, 63 small size single nucleotide polymorphisms and indels as well as 7 large deletions and duplications were identified as being the pathogenic variants. The mutations identified by the present technique were identical with those previously identified through Sanger sequencing and Multiplex Ligation-dependent Probe Amplification.

CONCLUSIONS

We hereby demonstrated that the established platform as an accurate and high-throughput gene testing method which might be useful in the clinical diagnosis of monogenic diabetes.

Evolution- and structure-based computational strategy reveals the impact of deleterious missense mutations on MODY 2 (maturity-onset diabetes of the young, type 2)

Heterozygous mutations in the central glycolytic enzyme glucokinase (GCK) can result in an autosomal dominant inherited disease, namely maturity-onset diabetes of the young, type 2 (MODY 2). MODY 2 is characterised by early onset: it usually appears before 25 years of age and presents as a mild form of hyperglycaemia. In recent years, the number of known GCK mutations has markedly increased. As a result, interpreting which mutations cause a disease or confer susceptibility to a disease and characterising these deleterious mutations can be a difficult task in large-scale analyses and may be impossible when using a structural perspective. The laborious and time-consuming nature of the experimental analysis led us to attempt to develop a cost-effective computational pipeline for diabetic research that is based on the fundamentals of protein biophysics and that facilitates our understanding of the relationship between phenotypic effects and evolutionary processes. In this study, we investigate missense mutations in the GCK gene by using a wide array of evolution- and structure-based computational methods, such as SIFT, PolyPhen2, PhD-SNP, SNAP, SNPs&GO, fathmm, and Align GVGD. Based on the computational prediction scores obtained using these methods, three mutations, namely E70K, A188T, and W257R, were identified as highly deleterious on the basis of their effects on protein structure and function. Using the evolutionary conservation predictors Consurf and Scorecons, we further demonstrated that most of the predicted deleterious mutations, including E70K, A188T, and W257R, occur in highly conserved regions of GCK. The effects of the mutations on protein stability were computed using PoPMusic 2.1, I-mutant 3.0, and Dmutant. We also conducted molecular dynamics (MD) simulation analysis through in silico modelling to investigate the conformational differences between the native and the mutant proteins and found that the identified deleterious mutations alter the stability, flexibility, and solvent-accessible surface area of the protein. Furthermore, the functional role of each SNP in GCK was identified and characterised using SNPeffect 4.0, F-SNP, and FASTSNP. We hope that the observed results aid in the identification of disease-associated mutations that affect protein structure and function. Our in silico findings provide a new perspective on the role of GCK mutations in MODY2 from an evolution-based structure-centric point of view. The computational architecture described in this paper can be used to predict the most appropriate disease phenotypes for large-genome sequencing projects and to provide individualised drug therapy for complex diseases such as diabetes.

Genetics of diabetes--are we missing the genes or the disease?

Diabetes is a group of metabolic diseases characterized by hyperglycemia resulting from defects in insulin secretion, insulin action, or both. The chronic hyperglycemia of diabetes is associated with long-term damage, dysfunction, and failure of different organs, especially the eyes, kidneys, nerves, heart, and blood vessels. Several pathogenic processes are involved in the development of diabetes. These range from autoimmune destruction of the beta-cells of the pancreas with consequent insulin deficiency to abnormalities that result in resistance to insulin action (American Diabetes Association, 2011). The vast majority of cases of diabetes fall into two broad categories. In type 1 diabetes (T1D), the cause is an absolute deficiency of insulin secretion, whereas in type 2 diabetes (T2D), the cause is a combination of resistance to insulin action and an inadequate compensatory insulin secretory response. However, the subdivision into two main categories represents a simplification of the real situation, and research during the recent years has shown that the disease is much more heterogeneous than a simple subdivision into two major subtypes assumes. Worldwide prevalence figures estimate that there are 280 million diabetic patients in 2011 and more than 500 million in 2030 (http://www.diabetesatlas.org/). In Europe, about 6-8% of the population suffer from diabetes, of them about 90% has T2D and 10% T1D, thereby making T2D to the fastest increasing disease in Europe and worldwide. This epidemic has been ascribed to a collision between the genes and the environment. While our knowledge about the genes is clearly better for T1D than for T2D given the strong contribution of variation in the HLA region to the risk of T1D, the opposite is the case for T2D, where our knowledge about the environmental triggers (obesity, lack of exercise) is much better than the understanding of the underlying genetic causes. This lack of knowledge about the underlying genetic causes of diabetes is often referred to as missing heritability (Manolio et al., 2009) which exceeds 80% for T2D but less than 25% for T1D. In the following review, we will discuss potential sources of this missing heritability which also includes the possibility that our definition of diabetes and its subgroups is imprecise and thereby making the identification of genetic causes difficult.

Cost-effectiveness of MODY genetic testing: translating genomic advances into practical health applications

OBJECTIVE To evaluate the cost-effectiveness of a genetic testing policy for HNF1A-, HNF4A-, and GCK-MODY in a hypothetical cohort of type 2 diabetic patients 25-40 years old with a MODY prevalence of 2%. RESEARCH DESIGN AND METHODS We used a simulation model of type 2 diabetes complications based on UK Prospective Diabetes Study data, modified to account for the natural history of disease by genetic subtype to compare a policy of genetic testing at diabetes diagnosis versus a policy of no testing. Under the screening policy, successful sulfonylurea treatment of HNF1A-MODY and HNF4A-MODY was modeled to produce a glycosylated hemoglobin reduction of -1.5% compared with usual care. GCK-MODY received no therapy. Main outcome measures were costs and quality-adjusted life years (QALYs) based on lifetime risk of complications and treatments, expressed as the incremental cost-effectiveness ratio (ICER) (USD/QALY). RESULTS The testing policy yielded an average gain of 0.012 QALYs and resulted in an ICER of 205,000 USD. Sensitivity analysis showed that if the MODY prevalence was 6%, the ICER would be ~50,000 USD. If MODY prevalence was >30%, the testing policy was cost saving. Reducing genetic testing costs to 700 USD also resulted in an ICER of ~50,000 USD. CONCLUSIONS Our simulated model suggests that a policy of testing for MODY in selected populations is cost-effective for the U.S. based on contemporary ICER thresholds. Higher prevalence of MODY in the tested population or decreased testing costs would enhance cost-effectiveness. Our results make a compelling argument for routine coverage of genetic testing in patients with high clinical suspicion of MODY.

Clinical follow-up of two Brazilian subjects with glucokinase-MODY (MODY2) with description of a novel mutation

Mutations in the glucokinase gene (GCK) account for many cases of monogenic diabetes featuring maturity-onset diabetes of the young type 2 (MODY2). The clinical pattern of this form of hyperglycemia is rather stable, with a slight elevation in blood glucose, which is usually not progressive. Patients rarely require pharmacological interventions and microvascular complications related to diabetes are unusual. We describe the clinical follow-up of two cases of MODY2 with two different mutations in GCK gene, one in exon 7, p.Glu265Lys (c.793 G> A), which has been previously described, and a novel one, in exon 2, p.Ser69Stop (c. 206C> G). The clinical course of both cases shows similarity in metabolic control of this form of diabetes over the years.

Incidental mild hyperglycemia in children: two MODY 2 families identified in Brazilian subjects

Maturity-onset diabetes of the young (MODY) is characterized by an autosomal dominant mode of inheritance, early onset of hyperglycemia, and defects of insulin secretion. MODY subtypes described present genetic, metabolic, and clinical differences. MODY 2 is characterized by mild asymptomatic fasting hyperglycemia, and rarely requires pharmacological treatment. Hence, precise diagnosis of MODY is important for determining management and prognosis. We report two heterozygous GCK mutations identified during the investigation of short stature. Case 1: a prepubertal 14-year-old boy was evaluated for constitutional delay of growth and puberty. During follow-up, he showed abnormal fasting glucose (113 mg/dL), increased level of HbA1c (6.6%), and negative β-cell antibodies. His father and two siblings also had slightly elevated blood glucose levels. The mother had normal glycemia. A GCK heterozygous missense mutation, p.Arg191Trp, was identified in the proband. Eighteen family members were screened for this mutation, and 11 had the mutation in heterozygous state. Case 2: a 4-year-old boy investigated for short stature revealed no other laboratorial alterations than elevated glycemia (118 mg/dL); β-cell antibodies were negative. His father, a paternal aunt, and the paternal grandmother also had slightly elevated glycemia, whereas his mother had normal glycemia. A GCK heterozygous missense mutation, p.Glu221Lys, was identified in the index patient and in four family members. All affected patients had mild elevated glycemia. Individuals with normal glycemia did not harbor mutations. GCK mutation screening should be considered in patients with chronic mild early-onset hyperglycemia, family history of impaired glycemia, and negative β-cell antibodies.

The spectrum of HNF1A gene mutations in Greek patients with MODY3: relative frequency and identification of seven novel germline mutations

OBJECTIVE

Maturity-Onset Diabetes of the Young (MODY) is the most common type of monogenic diabetes accounting for 1-2% of the population with diabetes. The relative incidence of HNF1A-MODY (MODY3) is high in European countries; however, data are not available for the Greek population. The aims of this study were to determine the relative frequency of MODY3 in Greece, the type of the mutations observed, and their relation to the phenotype of the patients.

DESIGN AND METHODS

Three hundred ninety-five patients were referred to our center because of suspected MODY during a period of 15 yr. The use of Denaturing Gradient Gel Electrophoresis of polymerase chain reaction amplified DNA revealed 72 patients carrying Glucokinase gene mutations (MODY2) and 8 patients carrying HNF1A gene mutations (MODY3). After using strict criteria, 54 patients were selected to be further evaluated by direct sequencing or by multiplex ligation probe amplification (MLPA) for the presence of HNF1A gene mutations.

RESULTS

In 16 unrelated patients and 13 of their relatives, 15 mutations were identified in the HNF1A gene. Eight of these mutations were previously reported, whereas seven were novel. Clinical features, such as age of diabetes at diagnosis or severity of hyperglycemia, were not related to the mutation type or location.

CONCLUSIONS

In our cohort of patients fulfilling strict clinical criteria for MODY, 12% carried an HNF1A gene mutation, suggesting that defects of this gene are responsible for a significant proportion of monogenic diabetes in the Greek population. No clear phenotype-genotype correlations were identified.

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.