Role of molecular genetics in transforming diagnosis of diabetes mellitus

Clinical and Genetic Characteristics of Congenital Hyperinsulinism in Norway: A Nationwide Cohort Study

PURPOSE

Congenital hyperinsulinism (CHI) is a rare, monogenic disease characterized by excessive insulin secretion. We aimed to evaluate all probands with suspected CHI in Norway registered over the past 2 decades.

METHODS

The study included 98 probands. Clinical data were cumulated from medical records. All probands were screened for variants in the genes ABCC8 and KCNJ11. Other CHI-related genes were Sanger-sequenced as indicated by the patients' phenotype (n = 75) or analyzed by next-generation sequencing employing a panel of 30 CHI-related genes (n = 23).

RESULTS

Twenty-one probands (21%) received a diagnosis other than CHI, the most common being idiopathic ketotic hypoglycemia (9%) or syndromic hyperinsulinism (4%). In the final cohort of 77 CHI probands, genetic findings were revealed in 46 (60%). ABCC8 variants were most common (n= 40), and 5 novel variants were identified. One proband harbored both the pathogenic GCK variant p.(Ala456Val) and the ABCC8 variant p.(Gly505Cys). Although most ABCC8 variants caused immediate disease onset with severe hypoglycemia and were diazoxide-unresponsive, 8 probands had a heterozygous, apparently dominant variant with milder phenotype. Two probands had pathogenic variants in GLUD1, whereas variants in HADH, HNF4A, KCNJ11, and HK1 were identified in 1 proband each, the latter being noncoding. Neurologic sequelae were reported in 53% of the CHI probands. Of nonsurgically treated probands, 43% had spontaneous resolution. The minimum birth prevalence of CHI in Norway is 1:19,400 live births.

MAIN CONCLUSION

Individuals with disease-causing ABCC8 variants dominated our cohort. Patients with known genetic etiology had earlier and more severe disease onset than genetically unsolved patients.

Social determinants of participation in genetic research among Puerto Ricans and in the Puerto Rican diaspora

Puerto Ricans are underrepresented in genetic research. This underrepresentation denies Puerto Ricans the benefit from therapeutic developments that could mitigate health disparities arising from conditions for which genetically-derived treatments exist. The Puerto Rican diaspora, especially post-2017 due to economic and environmental crises, has expanded within the USA. Prior research suggests that Latin American diaspora communities are less likely to participate in genetic research. We hypothesized, specifically, that the Puerto Rican diaspora in the USA would be less likely to participate in genetic research than would Puerto Ricans in their homeland's archipelago, and that accounting for social and cultural determinants related to the diaspora experience would mitigate this disparity. We implemented an analytical cross-sectional study of archipelago-residing Puerto Ricans and of the USA-residing diaspora to evaluate this hypothesis. With 1582 Puerto Ricans (723 in Puerto Rico, 859 in the USA), we found that while most participants would participate in genetic research, participation rates varied significantly by diaspora status. Puerto Ricans born and living in the USA were initially more likely to decline participation compared to those in Puerto Rico (OR = 1.54, p < 0.01). However, once adjusted for social and cultural variables, this difference was eliminated (aOR = 1.08, p = n.s.). The factors influencing non-participation include oppression, discrimination, distrust, and social determinants, aligning with the theory of minoritization. An important community in the USA and in the world, Puerto Ricans have the right to participate in well-conducted research and to benefit from its findings, particularly around topics that could help address existing disparities in health outcomes.

Two New Mutations in the CEL Gene Causing Diabetes and Hereditary Pancreatitis: How to Correctly Identify MODY8 Cases

CONTEXT

Maturity onset diabetes of the young, type 8 (MODY8) is associated with mutations in the CEL gene, which encodes the digestive enzyme carboxyl ester lipase. Several diabetes cases and families have in recent years been attributed to mutations in CEL without any functional or clinical evidence provided.

OBJECTIVE

To facilitate correct MODY8 diagnostics, we screened 2 cohorts of diabetes patients and delineated the phenotype.

METHODS

Young, lean Swedish and Finnish patients with a diagnosis of type 2 diabetes (352 cases, 406 controls) were screened for mutations in the CEL gene. We also screened 58 Czech MODY cases who had tested negative for common MODY genes. For CEL mutation-positive subjects, family history was recorded, and clinical investigations and pancreatic imaging performed.

RESULTS

Two cases (1 Swedish and 1 Czech) with germline mutation in CEL were identified. Clinical and radiological investigations of these 2 probands and their families revealed dominantly inherited insulin-dependent diabetes, pancreatic exocrine dysfunction, and atrophic pancreas with lipomatosis and cysts. Notably, hereditary pancreatitis was the predominant phenotype in 1 pedigree. Both families carried single-base pair deletions in the proximal part of the CEL variable number of tandem repeat (VNTR) region in exon 11. The mutations are predicted to lead to aberrant protein tails that make the CEL protein susceptible to aggregation.

CONCLUSION

The diagnosis of MODY8 requires a pancreatic exocrine phenotype and a deletion in the CEL VNTR in addition to dominantly inherited diabetes. CEL screening may be warranted also in families with hereditary pancreatitis of unknown genetic etiology.

A Comprehensive Analysis of Hungarian MODY Patients-Part I: Gene Panel Sequencing Reveals Pathogenic Mutations in HNF1A, HNF1B, HNF4A, ABCC8 and INS Genes

Maturity-onset diabetes of the young (MODY) has about a dozen known causal genes to date, the most common ones being HNF1A, HNF4A, HNF1B and GCK. The phenotype of this clinically and genetically heterogeneous form of diabetes depends on the gene in which the patient has the mutation. We have tested 450 Hungarian index patients with suspected MODY diagnosis with Sanger sequencing and next-generation sequencing and found a roughly 30% positivity rate. More than 70% of disease-causing mutations were found in the GCK gene, about 20% in the HNF1A gene and less than 10% in other MODY-causing genes. We found 8 pathogenic and 9 likely pathogenic mutations in the HNF1A gene in a total of 48 patients and family members. In the case of HNF1A-MODY, the recommended first-line treatment is low dose sulfonylurea but according to our data, the majority of our patients had been on unnecessary insulin therapy at the time of requesting their genetic testing. Our data highlights the importance of genetic testing in the diagnosis of MODY and the establishment of the MODY subtype in order to choose the most appropriate treatment.

Etiologic distribution and clinical characteristics of pediatric diabetes in 276 children and adolescents with diabetes at a single academic center

Background

The prevalence of monogenic diabetes is estimated to be 1.1–6.3% of patients with diabetes mellitus (DM) in Europe. The overlapping clinical features of various forms of diabetes make differential diagnosis challenging. Therefore, this study investigated the etiologic distribution and clinical characteristics of pediatric diabetes, including monogenic diabetes, who presented at a single tertiary center over the last 20 years.

Methods

This study included 276 consecutive patients with DM diagnosed before 18 years of age from January 2000 to December 2019 in Korea. Clinical features, biochemical findings, β-cell autoantibodies, and molecular characteristics were reviewed retrospectively.

Results

Of the 276 patients, 206 patients (74.6%), 49 patients (17.8%), and 21 patients (7.6%) were diagnosed with type 1 DM, type 2 DM, and clinically suspected monogenic diabetes, respectively. Among 21 patients suspected to have monogenic diabetes, 8 patients had clinical maturity-onset diabetes of the young (MODY), and the remaining 13 patients had other types of monogenic diabetes. Among them, genetic etiologies were identified in 14 patients (5.1%) from 13 families, which included MODY 5, transient neonatal DM, developmental delay, epilepsy, and neonatal diabetes (DEND) syndrome, Wolfram syndrome, Donohue syndrome, immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome, Fanconi-Bickel syndrome, Wolcott-Rallison syndrome, cystic fibrosis-related diabetes, and maternally inherited diabetes and deafness.

Conclusions

Genetically confirmed monogenic diabetes accounted for 5.1% of patients evaluated at a single tertiary center over 20-year period. Based on the findings for our sample, the frequency of mutations in the major genes of MODY appears to be low among pediatric patients in Korea. It is critical to identify the genetic cause of DM to provide appropriate therapeutic options and genetic counseling.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12887-021-02575-6.

Incidence of HNF1A and GCK MODY Variants in a South African Population

BACKGROUND AND AIM

Maturity-onset diabetes of the young (MODY) is the result of single gene variants. To date, fourteen different MODY subtypes have been described. Variants in genes coding for glucokinase (GCK, MODY2) and hepatic nuclear factor 1 alpha (HNF1A, MODY3) are most frequently encountered. MODY patients are often misdiagnosed with type 1 or type 2 diabetes, resulting in incorrect treatment protocols. At the time of reporting, no data are available on MODY prevalence in populations from Africa. Our study aimed to investigate and report on the incidence of MODY-related variants, specifically HNF1A variants, in a population from the Western Cape.

METHODS

Study participants were recruited (1643 in total, 407 males, 1236 females) and underwent anthropometric tests. Thereafter, blood was collected, and real-time PCR was used to screen for specific variants in HNF1A and GCK genes.

RESULTS

Ninety-seven individuals (5.9%) were identified with a specific HNF1A gene polymorphism (rs1169288) and twelve (0.9%) with a GCK polymorphism (rs4607517).

CONCLUSION

In total, 6.6% of the study population expressed MODY variants. To our knowledge, we are the first to report on MODY incidence in Africa. This research provides the basis for MODY incidence studies in South Africa, as well as data on non-Caucasian populations.

Genetics and Pathophysiology of Maturity-onset Diabetes of the Young (MODY): A Review of Current Trends

Single gene mutations have been implicated in the pathogenesis of a form of diabetes mellitus (DM) known as the maturity-onset diabetes of the young (MODY). However, there are diverse opinions on the suspect genes and pathophysiology, necessitating the need to review and communicate the genes to raise public awareness. We used the Google search engine to retrieve relevant information from reputable sources such as PubMed and Google Scholar. We identified 14 classified MODY genes as well as three new and unclassified genes linked with MODY. These genes are fundamentally embedded in the beta cells, the most common of which are HNF1A, HNF4A, HNF1B, and GCK genes. Mutations in these genes cause β-cell dysfunction, resulting in decreased insulin production and hyperglycemia. MODY genes have distinct mechanisms of action and phenotypic presentations compared with type 1 and type 2 DM and other forms of DM. Healthcare professionals are therefore advised to formulate drugs and treatment based on the causal genes rather than the current generalized treatment for all types of DM. This will increase the effectiveness of diabetes drugs and treatment and reduce the burden of the disease.

Response to multiple glucose-lowering agents in a sib-pair with a novel HNF1α (MODY3) variant

Maturity-onset diabetes of the young (MODY) is a genetically and clinically heterogeneous group of disorders characterised by early onset, lean, non-autoimmunity mediated, non-insulin-dependent diabetes often with autosomal-dominant inheritance and specific pharmaco-genetic response. We describe two siblings with HNF1A-MODY (MODY3) due to a novel germline variant p.(His126Asp) which segregates with diabetes in the family. However, contrary to anticipated therapeutic response, blood glucose in this sib-pair did not respond to sulphonylureas (both low and high dose), dipeptidyl peptidase-4 inhibitors (DPP-4 inhibitors), and glucagon-like peptide-1 receptor agonists (GLP-1RA), also known as incretin mimetics. The unexpected limited pharmaco-therapeutic response could potentially be unique to this specific variant and/or progressive pancreatic β-cell failure associated with long-standing disease duration, higher BMI and glucose-toxicity. Therefore, we report a novel-variant MODY3 sib-pair with atypical pharmaco-therapeutic response i.e. resistant to multiple anti-diabetes agents namely sulphonylurea, DPP-4 inhibitors and GLP-1RA treatment.

Comprehensive genetic screening: The prevalence of maturity-onset diabetes of the young gene variants in a population-based childhood diabetes cohort

BACKGROUND

Maturity-onset diabetes of the young (MODY) is caused by autosomal dominant mutations in one of 13 confirmed genes. Estimates of MODY prevalence vary widely, as genetic screening is usually restricted based on clinical features, even in population studies. We aimed to determine prevalence of MODY variants in a large and unselected pediatric diabetes cohort.

METHODS

MODY variants were assessed using massively parallel sequencing in the population-based diabetes cohort (n = 1363) of the sole tertiary pediatric diabetes service for Western Australia (population 2.6 million). All individuals were screened, irrespective of clinical features. MODY variants were also assessed in a control cohort (n = 993).

RESULTS

DNA and signed consent were available for 821 children. Seventeen children had pathogenic/likely pathogenic variants in MODY genes, two diagnosed with type 2 diabetes, four diagnosed with antibody-negative type 1 diabetes (T1DM), three diagnosed with antibody-positive T1DM, and eight previously diagnosed with MODY. Prevalence of MODY variants in the sequenced cohort was 2.1%, compared to 0.3% of controls.

CONCLUSIONS

This is the first comprehensive study of MODY variants in an unselected population-based pediatric diabetes cohort. The observed prevalence, increasing access to rapid and affordable genetic screening, and significant clinical implications suggest that genetic screening for MODY could be considered for all children with diabetes, irrespective of other clinical features.

Cost-effectiveness Analysis of Routine Screening Using Massively Parallel Sequencing for Maturity-Onset Diabetes of the Young in a Pediatric Diabetes Cohort: Reduced Health System Costs and Improved Patient Quality of Life

OBJECTIVE

Maturity-onset diabetes of the young (MODY) is an autosomal dominant form of diabetes, with multiple causative genes. Some MODY subtypes can be treated with sulfonylureas instead of insulin, improving glycemic control, complication rates, quality of life (QoL), and costs. Using massively parallel sequencing (MPS), we recently determined the prevalence of pathogenic/likely pathogenic MODY variants in an Australian pediatric diabetes cohort. Here, these data are used to estimate cost-effectiveness of using MPS for MODY in all pediatric diabetes cases compared with standard practice (sequencing limited to individuals with specific clinical features).

RESEARCH DESIGN AND METHODS

A Markov decision model was developed to estimate incremental costs and quality-adjusted life-years (QALYs) of MPS screening, modeled over 30 years. We used our observed prevalence of 2.14% compared with 0.7% for standard practice, based on published data. The probabilities and utility weightings of long-term diabetes complications were based on HbA_1c and estimated from published data. A series of one-way sensitivity analyses were performed using the net monetary benefit framework.

RESULTS

Routine MPS screening for MODY was more effective and less costly than standard care screening, with 26 QALYs gained and 1,016,000 AUD (782,000 USD) saved per 1,000 patients. Cost of screening was fully offset within 10 years. Routine MPS screening remained dominant until MODY prevalence fell to <1.1%.

CONCLUSIONS

Routine MPS screening for MODY in the pediatric population with diabetes could reduce health system costs and improve patient QoL. Our results make a compelling argument for routine genetic screening in all children with presumed type 1 diabetes mellitus.

A Systematic Review of Childhood Diabetes Research in the Middle East Region

Background: Diabetes mellitus (DM) is a common chronic disorder in children and is caused by absolute or relative insulin deficiency, with or without insulin resistance. There are several different forms of childhood DM. Children can suffer from neonatal diabetes mellitus (NDM), type 1 diabetes (T1DM), type 2 diabetes (T2DM), Maturity Onset Diabetes of the Young (MODY), autoimmune monogenic, mitochondrial, syndromic and as yet unclassified forms of DM. The Middle East has one of the highest incidences of several types of DM in children; however, it is unclear whether pediatric diabetes is an active area of research in the Middle East and if ongoing, which research areas are of priority for DM in children. Objectives: To review the literature on childhood DM related to research in the Middle East, summarize results, identify opportunities for research and make observations and recommendations for collaborative studies in pediatric DM. Methods: We conducted a thorough and systematic literature review by adhering to a list recommended by PRISMA. We retrieved original papers written in English that focus on childhood DM research, using electronic bibliographic databases containing publications from the year 2000 until October 2018. For our final assessment, we retrieved 429 full-text articles and selected 95 articles, based on our inclusion and exclusion criteria. Results: Our literature review suggests that childhood DM research undertaken in the Middle East has focused mainly on reporting retrospective review of case notes, a few prospective case studies, systemic reviews, questionnaire-based studies, and case reports. These reported studies have focused mostly on the incidence/prevalence of different types of DM in childhood. No studies report on the establishment of National Childhood Diabetes Registries. There is a lack of consolidated studies focusing on national epidemiology data of different types of childhood DM (such as NDM, T1DM, T2DM, MODY, and syndromic forms) and no studies reporting on clinical trials in children with DM. Conclusions: Investing in and funding basic and translational childhood diabetes research and encouraging collaborative studies, will bring enormous benefits financially, economically, and socially for the whole of the Middle East region.

Primary male factor infertility due to asthenospermia in maturity-onset diabetes of the young type 5 (MODY 5): uncommon presentation of an uncommon disease

Mutations in hepatocyte nuclear factor-1β gene result in a multisystemic syndrome where a monogenic form of diabetes (maturity-onset diabetes of young type 5; MODY 5) and renal anomalies, usually bilateral multiple cysts are the most characteristic findings. Many of them have pancreatic structural abnormalities as well. A plethora of extrapancreatic manifestations like altered liver function tests, hypomagnesaemia, hyperuricaemia with/without gout and urogenital malformations, particularly in females are also components of the syndrome. Structural malformation of male urogenital tract is rare in MODY 5, even rarer is asthenospermia. We encountered a young non-obese individual having insulin-requiring diabetes following secondary oral agent failure with primary male factor infertility secondary to asthenospermia. A suggestive family history, lack of acanthosis, negative pancreatic autoimmunity, hypomagnesaemia, bilateral renal and epididymal cysts, and absence of body and tail of pancreas pointed towards underlying MODY 5.

The role of the carboxyl ester lipase (CEL) gene in pancreatic disease

The enzyme carboxyl ester lipase (CEL), also known as bile salt-dependent or -stimulated lipase (BSDL, BSSL), hydrolyzes dietary fat, cholesteryl esters and fat-soluble vitamins in the duodenum. CEL is mainly expressed in pancreatic acinar cells and lactating mammary glands. The human CEL gene resides on chromosome 9q34.3 and contains a variable number of tandem repeats (VNTR) region that encodes a mucin-like protein tail. Although the number of normal repeats does not appear to significantly influence the risk for pancreatic disease, single-base pair deletions in the first VNTR repeat cause a syndrome of endocrine and exocrine dysfunction denoted MODY8. Hallmarks are low fecal elastase levels and pancreatic lipomatosis manifesting before the age of twenty, followed by development of diabetes and pancreatic cysts later in life. The mutant protein forms intracellular and extracellular aggregates, suggesting that MODY8 is a protein misfolding disease. Recently, a recombined allele between CEL and its pseudogene CELP was discovered. This allele (CEL-HYB) encodes a chimeric protein with impaired secretion increasing five-fold the risk for chronic pancreatitis. The CEL gene has proven to be exceptionally polymorphic due to copy number variants of the CEL-CELP locus and alterations involving the VNTR. Genome-wide association studies or deep sequencing cannot easily pick up this wealth of genetic variation. CEL is therefore an attractive candidate gene for further exploration of links to pancreatic disease.

The HNF1A mutant Ala180Val: Clinical challenges in determining causality of a rare HNF1A variant in familial diabetes

AIMS

Heterozygous mutations in hepatocyte nuclear factor-1A (HNF1A) cause maturity-onset diabetes of the young type 3 (MODY3). Our aim was to compare two families with suspected dominantly inherited diabetes and a new HNF1A variant of unknown clinical significance.

METHODS

The HNF1A gene was sequenced in two independently recruited families from the Norwegian MODY Registry. Both familes were phenotyped clinically and biochemically. Microsatellite markers around and within the HNF1A locus were used for haplotyping. Chromosomal linkage analysis was performed in one family, and whole-exome sequencing was undertaken in two affected family members from each family. Transactivation activity, DNA binding and nuclear localization of wild type and mutant HNF-1A were assessed.

RESULTS

The novel HNF1A variant c.539C>T (p.Ala180Val) was found in both families. The variant fully co-segregated with diabetes in one family. In the other family, two subjects with diabetes mellitus and one with normal glucose levels were homozygous variant carriers. Chromosomal linkage of diabetes to the HNF1A locus or to other genomic regions could not be established. The protein functional studies did not reveal significant differences between wild type and variant HNF-1A. In each family, whole-exome sequencing failed to identify any other variant that could explain the disease.

CONCLUSIONS

The HNF1A variant p.Ala180Val does not seem to cause MODY3, although it may confer risk for type 2 diabetes mellitus. Our data demonstrate challenges in causality evaluation of rare variants detected in known diabetes genes.

Targeted next-generation sequencing reveals MODY in up to 6.5% of antibody-negative diabetes cases listed in the Norwegian Childhood Diabetes Registry

AIMS/HYPOTHESIS

MODY can be wrongly diagnosed as type 1 diabetes in children. We aimed to find the prevalence of MODY in a nationwide population-based registry of childhood diabetes.

METHODS

Using next-generation sequencing, we screened the HNF1A, HNF4A, HNF1B, GCK and INS genes in all 469 children (12.1%) negative for both GAD and IA-2 autoantibodies and 469 antibody-positive matched controls selected from the Norwegian Childhood Diabetes Registry (3882 children). Variants were classified using clinical diagnostic criteria for pathogenicity ranging from class 1 (neutral) to class 5 (pathogenic).

RESULTS

We identified 58 rare exonic and splice variants in cases and controls. Among antibody-negative patients, 6.5% had genetic variants of classes 3-5 (vs 2.4% in controls; p = 0.002). For the stricter classification (classes 4 and 5), the corresponding number was 4.1% (vs 0.2% in controls; p = 1.6 × 10^-5). HNF1A showed the strongest enrichment of class 3-5 variants, with 3.9% among antibody-negative patients (vs 0.4% in controls; p = 0.0002). Antibody-negative carriers of variants in class 3 had a similar phenotype to those carrying variants in classes 4 and 5.

CONCLUSIONS/INTERPRETATION

This is the first study screening for MODY in all antibody-negative children in a nationwide population-based registry. Our results suggest that the prevalence of MODY in antibody-negative childhood diabetes may reach 6.5%. One-third of these MODY cases had not been recognised by clinicians. Since a precise diagnosis is important for treatment and genetic counselling, molecular screening of all antibody-negative children should be considered in routine diagnostics.

Functional Investigations of HNF1A Identify Rare Variants as Risk Factors for Type 2 Diabetes in the General Population

Variants in HNF1A encoding hepatocyte nuclear factor 1α (HNF-1A) are associated with maturity-onset diabetes of the young form 3 (MODY 3) and type 2 diabetes. We investigated whether functional classification of HNF1A rare coding variants can inform models of diabetes risk prediction in the general population by analyzing the effect of 27 HNF1A variants identified in well-phenotyped populations (n = 4,115). Bioinformatics tools classified 11 variants as likely pathogenic and showed no association with diabetes risk (combined minor allele frequency [MAF] 0.22%; odds ratio [OR] 2.02; 95% CI 0.73-5.60; P = 0.18). However, a different set of 11 variants that reduced HNF-1A transcriptional activity to <60% of normal (wild-type) activity was strongly associated with diabetes in the general population (combined MAF 0.22%; OR 5.04; 95% CI 1.99-12.80; P = 0.0007). Our functional investigations indicate that 0.44% of the population carry HNF1A variants that result in a substantially increased risk for developing diabetes. These results suggest that functional characterization of variants within MODY genes may overcome the limitations of bioinformatics tools for the purposes of presymptomatic diabetes risk prediction in the general population.

Paul T, Jose R, Regi A, Lionel J, Jeyaseelan L, Mathew J, Thomas N. Comprehensive Maturity Onset Diabetes of the Young (MODY) Gene Screening in Pregnant Women with Diabetes in India

Pregnant women with diabetes may have underlying beta cell dysfunction due to mutations/rare variants in genes associated with Maturity Onset Diabetes of the Young (MODY). MODY gene screening would reveal those women genetically predisposed and previously unrecognized with a monogenic form of diabetes for further clinical management, family screening and genetic counselling. However, there are minimal data available on MODY gene variants in pregnant women with diabetes from India. In this study, utilizing the Next generation sequencing (NGS) based protocol fifty subjects were screened for variants in a panel of thirteen MODY genes. Of these subjects 18% (9/50) were positive for definite or likely pathogenic or uncertain MODY variants. The majority of these variants was identified in subjects with autosomal dominant family history, of whom five were in women with pre-GDM and four with overt-GDM. The identified variants included one patient with HNF1A Ser3Cys, two PDX1 Glu224Lys, His94Gln, two NEUROD1 Glu59Gln, Phe318Ser, one INS Gly44Arg, one GCK, one ABCC8 Arg620Cys and one BLK Val418Met variants. In addition, three of the seven offspring screened were positive for the identified variant. These identified variants were further confirmed by Sanger sequencing. In conclusion, these findings in pregnant women with diabetes, imply that a proportion of GDM patients with autosomal dominant family history may have MODY. Further NGS based comprehensive studies with larger samples are required to confirm these finding.

Branched Fatty Acid Esters of Hydroxy Fatty Acids Are Preferred Substrates of the MODY8 Protein Carboxyl Ester Lipase

A recently discovered class of endogenous mammalian lipids, branched fatty acid esters of hydroxy fatty acids (FAHFAs), possesses anti-diabetic and anti-inflammatory activities. Here, we identified and validated carboxyl ester lipase (CEL), a pancreatic enzyme hydrolyzing cholesteryl esters and other dietary lipids, as a FAHFA hydrolase. Variants of CEL have been linked to maturity-onset diabetes of the young, type 8 (MODY8), and to chronic pancreatitis. We tested the FAHFA hydrolysis activity of the CEL MODY8 variant and found a modest increase in activity as compared with that of the normal enzyme. Together, the data suggest that CEL might break down dietary FAHFAs.

Common and rare forms of diabetes mellitus: towards a continuum of diabetes subtypes

Insights into the genetic basis of type 2 diabetes mellitus (T2DM) have been difficult to discern, despite substantial research. More is known about rare forms of diabetes mellitus, several of which share clinical and genetic features with the common form of T2DM. In this Review, we discuss the extent to which the study of rare and low-frequency mutations in large populations has begun to bridge the gap between rare and common forms of diabetes mellitus. We hypothesize that the perceived division between these diseases might be due, in part, to the historical ascertainment bias of genetic studies, rather than a clear distinction between disease pathophysiologies. We also discuss possible implications of a new model for the genetic basis of diabetes mellitus subtypes, where the boundary between subtypes becomes blurred.

Molecular diagnosis of maturity-onset diabetes of the young (MODY) in Turkish children by using targeted next-generation sequencing

AIM

To perform molecular analysis of pediatric maturity onset diabetes of the young (MODY) patients by next-generation sequencing, which enables simultaneous analysis of multiple genes in a single test, to determine the genetic etiology of a group of Turkish children clinically diagnosed as MODY, and to assess genotype-phenotype relationship.

METHODS

Forty-two children diagnosed with MODY and their parents were enrolled in the study. Clinical and laboratory characteristics of the patients at the time of diagnosis were obtained from hospital records. Molecular analyses of GCK, HNF1A, HNF4A, HNF1B, PDX1, NEUROD1, KLF11, CEL, PAX4, INS, and BLK genes were performed on genomic DNA by using next-generation sequencing. Pathogenicity for novel mutations was assessed by bioinformatics prediction software programs and segregation analyses.

RESULTS

A mutation in MODY genes was identified in 12 (29%) of the cases. GCK mutations were detected in eight cases, and HNF1B, HNF1A, PDX1, and BLK mutations in the others. We identified five novel missense mutations - three in GCK (p.Val338Met, p.Cys252Ser, and p.Val86Ala), one in HNF1A (p.Cys241Ter), and one in PDX1 (p.Gly55Asp), which we believe to be pathogenic.

CONCLUSION

The results of this study showed that mutations in the GCK gene are the leading cause of MODY in our population. Moreover, genetic diagnosis could be made in 29% of Turkish patients, and five novel mutations were identified.

Gamut of genetic testing for neonatal care

The field of clinical genetics has advanced at an unprecedented pace. Today, with the aid of several high-resolution and high-precision technologies, physicians are able to make molecular genetic diagnoses for many infants affected with genetic disease. It is imperative, however, that perinatologists and neonatologists understand the strengths and limitations of genetic testing. This article discusses the different genetic testing options available for perinatal and neonatal diagnostics, along with their clinical utilities and indications. From variant-specific testing to whole-exome and genome sequencing, the article covers the whole gamut of genetic testing, with some thoughts on the changing paradigm of medical genetics.

Maturity-onset diabetes of the young (MODY): an update

Maturity-onset diabetes of the young (MODY) is a group of monogenic disorders characterized by autosomal dominantly inherited non-insulin dependent form of diabetes classically presenting in adolescence or young adults before the age of 25 years. MODY is a rare cause of diabetes (1% of all cases) and is frequently misdiagnosed as Type 1 diabetes (T1DM) or Type 2 diabetes (T2DM). A precise molecular diagnosis is essential because it leads to optimal treatment of the patients and allows early diagnosis for their asymptomatic family members. Mutations in the glucokinase (GCK) (MODY 2) and hepatocyte nuclear factor (HNF)1A/4A (MODY 3 and MODY 1) genes are the most common causes of MODY. GCK mutations cause a mild, asymptomatic, and stable fasting hyperglycemia usually requiring no specific treatment. However, mutations in the HNF1A and HNF4A cause a progressive pancreatic β-cell dysfunction and hyperglycemia that can result in microvascular complications. Sulfonylureas are effective in these patients by acting on adenosine triphosphate (ATP)-sensitive potassium channels, although insulin therapy may be required later in life. Mutations in the HNF1B (MODY 5) is associated with pancreatic agenesis, renal abnormalities, genital tract malformations, and liver dysfunction. Compared to MODY 1, 2, 3, and 5, the remaining subtypes of MODY have a much lower prevalence. In this review, we summarize the main clinical and laboratory characteristics of the common and rarer causes of MODY.

E23K variant in KCNJ11 gene is associated with susceptibility to type 2 diabetes in the Mauritanian population

AIMS

Many genetic association studies reported the contribution of KCNJ11 gene to type 2 diabetes susceptibility in different populations. We aimed to evaluate the association between E23K variant of KCNJ11 and type 2 diabetes in the Mauritanian population.

MATERIALS AND METHODS

We performed a case-control association study including 135 type 2 diabetes Mauritanian patients and 135 controls. Genotyping for the E23K variant was performed using a TaqMan allelic discrimination assay.

RESULTS

We found significant association between KCNJ11 E23K variant and type 2 diabetes (Global model, OR=2.08, 95% CI=1.09-3.97, p=0.026). In the Moor ethnic group, E23K was also associated with type 2 diabetes in the general model (OR=2.08, 95% CI=1.09-3.97, p=0.026) and under the dominant model (OR=2.49, 95% CI=1.12-5.55, p=0.026). In the Mauritanians of African descent, KK genotype was not found. Besides, E23K variant was not associated with type 2 diabetes (OR=0.69, 95% CI=0.04-11.32, p=0.793).

CONCLUSIONS

Our results revealed the risk of type 2 diabetes conferred by KCNJ11 E23K gene variant in the Mauritanian population.

Association of a low-frequency variant in HNF1A with type 2 diabetes in a Latino population

IMPORTANCE

Latino populations have one of the highest prevalences of type 2 diabetes worldwide.

OBJECTIVES

To investigate the association between rare protein-coding genetic variants and prevalence of type 2 diabetes in a large Latino population and to explore potential molecular and physiological mechanisms for the observed relationships.

DESIGN, SETTING, AND PARTICIPANTS

Whole-exome sequencing was performed on DNA samples from 3756 Mexican and US Latino individuals (1794 with type 2 diabetes and 1962 without diabetes) recruited from 1993 to 2013. One variant was further tested for allele frequency and association with type 2 diabetes in large multiethnic data sets of 14,276 participants and characterized in experimental assays.

MAIN OUTCOME AND MEASURES

Prevalence of type 2 diabetes. Secondary outcomes included age of onset, body mass index, and effect on protein function.

RESULTS

A single rare missense variant (c.1522G>A [p.E508K]) was associated with type 2 diabetes prevalence (odds ratio [OR], 5.48; 95% CI, 2.83-10.61; P = 4.4 × 10(-7)) in hepatocyte nuclear factor 1-α (HNF1A), the gene responsible for maturity onset diabetes of the young type 3 (MODY3). This variant was observed in 0.36% of participants without type 2 diabetes and 2.1% of participants with it. In multiethnic replication data sets, the p.E508K variant was seen only in Latino patients (n = 1443 with type 2 diabetes and 1673 without it) and was associated with type 2 diabetes (OR, 4.16; 95% CI, 1.75-9.92; P = .0013). In experimental assays, HNF-1A protein encoding the p.E508K mutant demonstrated reduced transactivation activity of its target promoter compared with a wild-type protein. In our data, carriers and noncarriers of the p.E508K mutation with type 2 diabetes had no significant differences in compared clinical characteristics, including age at onset. The mean (SD) age for carriers was 45.3 years (11.2) vs 47.5 years (11.5) for noncarriers (P = .49) and the mean (SD) BMI for carriers was 28.2 (5.5) vs 29.3 (5.3) for noncarriers (P = .19).

CONCLUSIONS AND RELEVANCE

Using whole-exome sequencing, we identified a single low-frequency variant in the MODY3-causing gene HNF1A that is associated with type 2 diabetes in Latino populations and may affect protein function. This finding may have implications for screening and therapeutic modification in this population, but additional studies are required.

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.

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.

A novel genetic mutation in a Portuguese family with GCK-MODY

INTRODUCTION

Maturity-onset diabetes of the young (MODY) is a genetically heterogeneous form of diabetes mellitus, with autosomal dominant inheritance. It accounts for 2%-5% of all diabetes cases. Glucokinase-MODY is the second most frequent form, which has been shown to be the result of mutations in the glucokinase (GCK) gene. It mostly presents with mild hyperglycemia, and, usually, no diabetes-related complications occur.

CASE REPORT

A 9-year-old female was admitted to the Endocrine Clinic to study her fasting hyperglycemia. Despite her obesity (body mass index 28 kg/m2), her physical examination had no other abnormalities. Blood tests showed a 6.3% hemoglobin A1c, with normal standard oral glucose tolerance test result, normal insulin value and normal C-peptide level. Insulin autoantibodies and antibodies against glutamate decarboxylase were negative. She began metformin and adequate diet. She had a strongly positive family history for diabetes. The patient's mother, uncle, grandfather, great-aunt and great-grandfather on her mother's side were diagnosed with diabetes. Complete sequencing of the GCK gene, carried out in the patient, identified a novel mutation c.1268T>A (p.Phe423Tyr) in exon 10 of the gene GCK in heterozygosity. Further studies revealed the same mutation in her mother and maternal grandfather.

CONCLUSION

Finding the same mutation in three different generations of diabetic patients, in the same family, is highly suggestive of its pathogenicity. To the authors' knowledge, this is the first time it is described in the literature. Correct molecular diagnosis of MODY predicts better the clinical course of diabetes and facilitates individualised management.

Autosomal dominant diabetes arising from a Wolfram syndrome 1 mutation

We used an unbiased genome-wide approach to identify exonic variants segregating with diabetes in a multigenerational Finnish family. At least eight members of this family presented with diabetes with age of diagnosis ranging from 18 to 51 years and a pattern suggesting autosomal dominant inheritance. We sequenced the exomes of four affected members of this family and performed follow-up genotyping of additional affected and unaffected family members. We uncovered a novel nonsynonymous variant (p.Trp314Arg) in the Wolfram syndrome 1 (WFS1) gene that segregates completely with the diabetic phenotype. Multipoint parametric linkage analysis with 13 members of this family identified a single linkage signal with maximum logarithm of odds score 3.01 at 4p16.2-p16.1, corresponding to a region harboring the WFS1 locus. Functional studies demonstrate a role for this variant in endoplasmic reticulum stress, which is consistent with the β-cell failure phenotype seen in mutation carriers. This represents the first compelling report of a mutation in WFS1 associated with dominantly inherited nonsyndromic adult-onset diabetes.

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.

Using genetic prediction from known complex disease Loci to guide the design of next-generation sequencing experiments

A central focus of complex disease genetics after genome-wide association studies (GWAS) is to identify low frequency and rare risk variants, which may account for an important fraction of disease heritability unexplained by GWAS. A profusion of studies using next-generation sequencing are seeking such risk alleles. We describe how already-known complex trait loci (largely from GWAS) can be used to guide the design of these new studies by selecting cases, controls, or families who are most likely to harbor undiscovered risk alleles. We show that genetic risk prediction can select unrelated cases from large cohorts who are enriched for unknown risk factors, or multiply-affected families that are more likely to harbor high-penetrance risk alleles. We derive the frequency of an undiscovered risk allele in selected cases and controls, and show how this relates to the variance explained by the risk score, the disease prevalence and the population frequency of the risk allele. We also describe a new method for informing the design of sequencing studies using genetic risk prediction in large partially-genotyped families using an extension of the Inside-Outside algorithm for inference on trees. We explore several study design scenarios using both simulated and real data, and show that in many cases genetic risk prediction can provide significant increases in power to detect low-frequency and rare risk alleles. The same approach can also be used to aid discovery of non-genetic risk factors, suggesting possible future utility of genetic risk prediction in conventional epidemiology. Software implementing the methods in this paper is available in the R package Mangrove.

An Egyptian family with H syndrome due to a novel mutation in SLC29A3 illustrating overlapping features with pigmented hypertrichotic dermatosis with insulin-dependent diabetes and Faisalabad histiocytosis

The SLC29A3 gene, encoding hENT3, a member of the equilibrative nucleoside transporter family, has recently been found mutated in Faisalabad histiocytosis, pigmented hypertrichotic dermatosis with insulin-dependent diabetes, familial sinus histiocytosis with massive lymphadenopathy (SHML), and H syndromes. We here report clinical and genetic findings of an Egyptian family with H syndrome. We describe two siblings, a 19-yr old girl and a 15-yr old boy, of consanguineous parents. From 5 yr of age, the girl developed bilateral flexion deformity of interphalengeal joints and insulin-dependent diabetes mellitus. At age 7 yr, prominent hyperpigmented patches appeared on the skin at lower limbs, genitalia, and trunk. On clinical examination, she had hepatosplenomegaly, generalized lymphadenopathy, left ventricular hypertrophy, sensorineural hearing loss, hypogonadism, short stature, and characteristic dysmorphic features. Her brother had fixed flexion contractures of the feet, profound sensorineural hearing loss, characteristic dysmorphic features, but no diabetes. DNA sequence analysis revealed a homozygous mutation (c.300+1G>C) in SLC29A3 in both siblings. The phenotype and genotype of the siblings were compatible with that of the H syndrome, although the features were overlapping with those found in pigmented hypertrichotic dermatosis with insulin-dependent diabetes, familial SHML, and Faisalabad histiocytosis, indicating that these four syndromes may be regarded as one disease with varying phenotypic features. A new, common name for these conditions is warranted.

Prevalence of monogenic diabetes in the population-based Norwegian Childhood Diabetes Registry

AIMS/HYPOTHESIS

Monogenic diabetes (MD) might be misdiagnosed as type 1 diabetes. The prevalence of MD among children with apparent type 1 diabetes has not been established. Our aim was to estimate the prevalence of common forms of MD in childhood diabetes.

METHODS

We investigated 2,756 children aged 0-14 years with newly diagnosed diabetes who had been recruited to the nationwide population-based Norwegian Childhood Diabetes Registry (NCDR), from July 2002 to March 2012. Completeness of ascertainment was 91%. Children diagnosed with diabetes who were under12 months of age were screened for mutations in KCNJ11, ABCC8 and INS. Children without GAD and protein tyrosine phosphatase-like protein antibodies were screened in two ways. Those who had a parent with diabetes were screened for mutations in HNF1A, HNF4A, INS and MT-TL1. Children with HbA1c <7.5% (<58 mmol/mol) and no insulin requirement were screened for mutations in GCK. Finally, we searched the Norwegian MODY Registry for children with genetically verified MD.

RESULTS

We identified 15 children harbouring a mutation in HNF1A, nine with one in GCK, four with one in KCNJ11, one child with a mutation in INS and none with a mutation in MT-TL1. The minimum prevalence of MD in the NCDR was therefore 1.1%. By searching the Norwegian MODY Registry, we found 24 children with glucokinase-MODY, 15 of whom were not present in the NCDR. We estimated the minimum prevalence of MD among Norwegian children to be 3.1/100,000.

CONCLUSIONS/INTERPRETATION

This is the first prevalence study of the common forms of MD in a nationwide, population-based registry of childhood diabetes. We found that 1.1% of patients in the Norwegian Childhood Diabetes Registry had MD.

Monogenic diabetes: old and new approaches to diagnosis

Up to 5% of young adults diagnosed with diabetes have a monogenic aetiology, the most common of which is maturity-onset diabetes of the young (MODY). A definitive molecular diagnosis is important, as this affects treatment, prognosis and family screening. Currently, however, rates of diagnosis are low due to a combination of lack of awareness of the benefits of making the diagnosis and the challenges of differentiating patients with MODY from those with common forms of diabetes. This article aims to introduce general physicians to the characteristics of monogenic diabetes and the clinical features that can be used to diagnose patients. Recently, genomewide association studies have resulted in the identification of C-reactive protein and glycan profile as specific biomarkers for the most common MODY subtype due to HNF1A mutations, and the potential translation of these findings are discussed.

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.

RD Lawrence lecture 2012: assessing aetiology in diabetes: how C-peptide, CRP and fucosylation came to the party!

Assigning the correct aetiology in diabetes is important for treatment, understanding prognosis and for follow-up of family members. Despite these benefits, many are missing out on the opportunity to have testing for monogenic forms of diabetes. This review gives the clinical features of the commoner forms of monogenic diabetes and examines which clinical and biological markers can be used to identify those at highest risk of having Maturity onset diabetes of the young (MODY). MODY is characterised by young-onset, familial diabetes which is C-peptide positive, β-cell antibody negative and not associated with metabolic syndrome. Differentiating from type 1 and type 2 diabetes can be challenging due to the overlap of clinical features. In type 1 diabetes, insulin production ceases after the honeymoon period. Thus C-peptide can be used to detect those with persisting insulin secretion who might have a different cause for their diabetes. In type 2 diabetes, most have insulin resistance, so absence of metabolic syndrome could be used to identify those most likely to have MODY. Another approach is to look for non-pancreatic features associated with mutations in MODY genes. Following results from Genome-wide association studies, we have shown that those with HNF1A mutations (the commonest form of MODY) have decreased serum levels of highly-sensitive C-reactive protein (hsCRP) and altered patterns of plasma protein fucosylation. These features can differentiate HNF1A-MODY from common forms of diabetes with a high degree of discriminative accuracy. Using combinations of clinical features and new biomarkers in diagnostic pathways will help increase diagnosis rates of MODY.

Epigenetic silencing of HNF1A associates with changes in the composition of the human plasma N-glycome

Protein glycosylation is a ubiquitous modification that affects the structure and function of proteins. Our recent genome wide association study identified transcription factor HNF1A as an important regulator of plasma protein glycosylation. To evaluate the potential impact of epigenetic regulation of HNF1A on protein glycosylation we analyzed CpG methylation in 810 individuals. The association between methylation of four CpG sites and the composition of plasma and IgG glycomes was analyzed. Several statistically significant associations were observed between HNF1A methylation and plasma glycans, while there were no significant associations with IgG glycans. The most consistent association with HNF1A methylation was observed with the increase in the proportion of highly branched glycans in the plasma N-glycome. The hypothesis that inactivation of HNF1A promotes branching of glycans was supported by the analysis of plasma N-glycomes in 61 patients with inactivating mutations in HNF1A, where the increase in plasma glycan branching was also observed. This study represents the first demonstration of epigenetic regulation of plasma glycome composition, suggesting a potential mechanism by which epigenetic deregulation of the glycome may contribute to disease development.

Systematic assessment of etiology in adults with a clinical diagnosis of young-onset type 2 diabetes is a successful strategy for identifying maturity-onset diabetes of the young

OBJECTIVE

Misdiagnosis of maturity-onset diabetes of the young (MODY) remains widespread, despite the benefits of optimized management. This cross-sectional study examined diagnostic misclassification of MODY in subjects with clinically labeled young adult-onset type 1 and type 2 diabetes by extending genetic testing beyond current guidelines.

RESEARCH DESIGN AND METHODS

Individuals were selected for diagnostic sequencing if they displayed features atypical for their diagnostic label. From 247 case subjects with clinically labeled type 1 diabetes, we sequenced hepatocyte nuclear factor 1 α (HNF1A) and hepatocyte nuclear factor 4 α (HNF4A) in 20 with residual β-cell function ≥ 3 years from diagnosis (random or glucagon-stimulated C-peptide ≥ 0.2 nmol/L). From 322 with clinically labeled type 2 diabetes, we sequenced HNF1A and HNF4A in 80 with diabetes diagnosed ≤ 30 years and/or diabetes diagnosed ≤ 45 years without metabolic syndrome. We also sequenced the glucokinase (GCK) in 40 subjects with mild fasting hyperglycemia.

RESULTS

In the type 1 diabetic group, two HNF1A mutations were found (0.8% prevalence). In type 2 diabetic subjects, 10 HNF1A, two HNF4A, and one GCK mutation were identified (4.0%). Only 47% of MODY case subjects identified met current guidelines for diagnostic sequencing. Follow-up revealed a further 12 mutation carriers among relatives. Twenty-seven percent of newly identified MODY subjects changed treatment, all with improved glycemic control (HbA(1c) 8.8 vs. 7.3% at 3 months; P = 0.02).

CONCLUSIONS

The systematic use of widened diagnostic testing criteria doubled the numbers of MODY case subjects identified compared with current clinical practice. The yield was greatest in young adult-onset type 2 diabetes. We recommend that all patients diagnosed before age 30 and with presence of C-peptide at 3 years' duration are considered for molecular diagnostic analysis.

Exome sequencing and genetic testing for MODY

CONTEXT

Genetic testing for monogenic diabetes is important for patient care. Given the extensive genetic and clinical heterogeneity of diabetes, exome sequencing might provide additional diagnostic potential when standard Sanger sequencing-based diagnostics is inconclusive.

OBJECTIVE

The aim of the study was to examine the performance of exome sequencing for a molecular diagnosis of MODY in patients who have undergone conventional diagnostic sequencing of candidate genes with negative results.

RESEARCH DESIGN AND METHODS

We performed exome enrichment followed by high-throughput sequencing in nine patients with suspected MODY. They were Sanger sequencing-negative for mutations in the HNF1A, HNF4A, GCK, HNF1B and INS genes. We excluded common, non-coding and synonymous gene variants, and performed in-depth analysis on filtered sequence variants in a pre-defined set of 111 genes implicated in glucose metabolism.

RESULTS

On average, we obtained 45 X median coverage of the entire targeted exome and found 199 rare coding variants per individual. We identified 0-4 rare non-synonymous and nonsense variants per individual in our a priori list of 111 candidate genes. Three of the variants were considered pathogenic (in ABCC8, HNF4A and PPARG, respectively), thus exome sequencing led to a genetic diagnosis in at least three of the nine patients. Approximately 91% of known heterozygous SNPs in the target exomes were detected, but we also found low coverage in some key diabetes genes using our current exome sequencing approach. Novel variants in the genes ARAP1, GLIS3, MADD, NOTCH2 and WFS1 need further investigation to reveal their possible role in diabetes.

CONCLUSION

Our results demonstrate that exome sequencing can improve molecular diagnostics of MODY when used as a complement to Sanger sequencing. However, improvements will be needed, especially concerning coverage, before the full potential of exome sequencing can be realized.

To test, or not to test: time for a MODY calculator?

To test, or not to test, that is often the question in diabetes genetics. This is why the paper of Shields et al in the current issue of Diabetologia is so warmly welcomed. MODY is the most common form of monogenic diabetes. Nevertheless, the optimal way of identifying MODY families still poses a challenge both for researchers and clinicians. Hattersley's group in Exeter, UK, have developed an easy-to-use MODY prediction model that can help to identify cases appropriate for genetic testing. By answering eight simple questions on the internet ( www.diabetesgenes.org/content/mody-probability-calculator ), the doctor receives a positive predictive value in return: the probability that the patient has MODY. Thus, the classical binary (yes/no) assessment provided by clinical diagnostic criteria has been substituted by a more rational, quantitative estimate. The model appears to discriminate well between MODY and type 1 and type 2 diabetes when diabetes is diagnosed before the age of 35 years. However, the performance of the MODY probability calculator should now be validated in other settings than where it was developed-and, as always, there is room for some improvements and modifications.

The role of pancreatic imaging in monogenic diabetes mellitus

In neonatal diabetes mellitus resulting from mutations in EIF2AK3, PTF1A, HNF1B, PDX1 or RFX6, pancreatic aplasia or hypoplasia is typical. In maturity-onset diabetes mellitus of the young (MODY), mutations in HNF1B result in aplasia of pancreatic body and tail, and mutations in CEL lead to lipomatosis. The pancreas is not readily accessible for histopathological investigations and pancreatic imaging might, therefore, prove important for diagnosis, treatment, and research into these β-cell diseases. Advanced imaging techniques can identify the pancreatic features that are characteristic of inherited diabetes subtypes, including alterations in organ size (diffuse atrophy and complete or partial pancreatic agenesis), lipomatosis and calcifications. Consequently, in patients with suspected monogenic diabetes mellitus, the results of pancreatic imaging could help guide the molecular and genetic investigation. Imaging findings also highlight the critical roles of specific genes in normal pancreatic development and differentiation and provide new insight into alterations in pancreatic structure that are relevant for β-cell disease.

Genetic risk prediction in complex disease

Attempting to classify patients into high or low risk for disease onset or outcomes is one of the cornerstones of epidemiology. For some (but by no means all) diseases, clinically usable risk prediction can be performed using classical risk factors such as body mass index, lipid levels, smoking status, family history and, under certain circumstances, genetics (e.g. BRCA1/2 in breast cancer). The advent of genome-wide association studies (GWAS) has led to the discovery of common risk loci for the majority of common diseases. These discoveries raise the possibility of using these variants for risk prediction in a clinical setting. We discuss the different ways in which the predictive accuracy of these loci can be measured, and survey the predictive accuracy of GWAS variants for 18 common diseases. We show that predictive accuracy from genetic models varies greatly across diseases, but that the range is similar to that of non-genetic risk-prediction models. We discuss what factors drive differences in predictive accuracy, and how much value these predictions add over classical predictive tests. We also review the uses and pitfalls of idealized models of risk prediction. Finally, we look forward towards possible future clinical implementation of genetic risk prediction, and discuss realistic expectations for future utility.