Insights From Molecular Characterization of Adult Patients of Families With Multigenerational Diabetes

A novel BLK heterozygous mutation (p.Met121lle) in maturity-onset diabetes mellitus: A case report and literature review

Maturity onset diabetes of the young (MODY) is a highly heterogeneous monogenic disease that occurs due to β-cell dysfunction. It is divided into different types depending on the gene mutated, and a total of 16 genes have been found to be associated with MODY. However, due to the current lack of understanding of monogenic diabetes, 90% of MODY is currently misdiagnosed and ignored in clinical practice. In this paper, we report the clinical data of a patient diagnosed with diabetes. Genetic testing revealed a novel BLK heterozygous mutation (c.363G>A) in the patient and in his father and son. He had no islet-specific autoantibodies and showed a reduced meal-induced response of insulin. Precise diagnosis of MODY individuals is important to the treatment.

The first exome wide association study in Tunisia: identification of candidate loci and pathways with biological relevance for type 2 diabetes

Introduction

Type 2 diabetes (T2D) is a multifactorial disease involving genetic and environmental components. Several genome-wide association studies (GWAS) have been conducted to decipher potential genetic aberrations promoting the onset of this metabolic disorder. These GWAS have identified over 400 associated variants, mostly in the intronic or intergenic regions. Recently, a growing number of exome genotyping or exome sequencing experiments have identified coding variants associated with T2D. Such studies were mainly conducted in European populations, and the few candidate-gene replication studies in North African populations revealed inconsistent results. In the present study, we aimed to discover the coding genetic etiology of T2D in the Tunisian population.

Methods

We carried out a pilot Exome Wide Association Study (EWAS) on 50 Tunisian individuals. Single variant analysis was performed as implemented in PLINK on potentially deleterious coding variants. Subsequently, we applied gene-based and gene-set analyses using MAGMA software to identify genes and pathways associated with T2D. Potential signals were further replicated in an existing large in-silico dataset, involving up to 177116 European individuals.

Results

Our analysis revealed, for the first time, promising associations between T2D and variations in MYORG gene, implicated in the skeletal muscle fiber development. Gene-set analysis identified two candidate pathways having nominal associations with T2D in our study samples, namely the positive regulation of neuron apoptotic process and the regulation of mucus secretion. These two pathways are implicated in the neurogenerative alterations and in the inflammatory mechanisms of metabolic diseases. In addition, replication analysis revealed nominal associations of the regulation of beta-cell development and the regulation of peptidase activity pathways with T2D, both in the Tunisian subjects and in the European in-silico dataset.

Conclusions

The present study is the first EWAS to investigate the impact of single genetic variants and their aggregate effects on T2D risk in Africa. The promising disease markers, revealed by our pilot EWAS, will promote the understanding of the T2D pathophysiology in North Africa as well as the discovery of potential treatments.

Genetic and Functional Analyses of the Novel KLF11 Pro193Thr Variant in a Three-Generation Family with MODY7

KLF11 regulates insulin gene expression through binding to the insulin promoter and has been reported as a causative gene for maturity-onset diabetes of the young 7 (MODY7). Here, we report a novel KLF11 variant associated with a three-generation family with early childhood-onset diabetes and explore its clinical and functional characteristics. The three-generational pedigree contains five patients affected by diabetes. The pathogenic variant identified by whole-exome sequencing was further confirmed by Sanger sequencing and pedigree verification. Luciferase reporter assays and glucose-stimulated insulin secretion were used to examine whether the KLF11 variant binds to the insulin promoter and regulate insulin secretion in vitro. The proband, his son, and his uncle exhibited hyperglycemia at ages 32, 13 and 71 years, respectively. All three patients showed characteristics of metabolic syndrome (obesity, dyslipidemia, and diabetes), but the insulin secretion of islet β-cells was impaired. A novel heterozygous missense variant, c.577 C>A (p.Pro193Thr) of the KLF11 gene was detected in all three patients. This variant co-segregates with the diabetes phenotype, consistent with an autosomal dominant disorder. The identified KLF11 p.Pro193Thr variant drastically decreased the transcriptional activity of KLF11, as demonstrated by luciferase reporter assay. Functional analyses revealed that the KLF11 Pro193Thr variant inhibited glucose-stimulated insulin secretion. We identified a novel KLF11 Pro193Thr variant in a three generation family with MODY7. These findings shed light on the molecular mechanisms underlying the pathogenesis of MODY7 and expand the genotype and clinical spectrum of MODY7.

Whole-genome sequencing of multiple related individuals with type 2 diabetes reveals an atypical likely pathogenic mutation in the PAX6 gene

Pathogenic variants in more than 14 genes have been implicated in monogenic diabetes; however, a significant fraction of individuals with young-onset diabetes and a strong family history of diabetes have unknown genetic etiology. To identify novel pathogenic alleles for monogenic diabetes, we performed whole-genome sequencing (WGS) on four related individuals with type 2 diabetes - including one individual diagnosed at the age of 31 years - that were negative for mutations in known monogenic diabetes genes. The individuals were ascertained from a large case-control study and had a multi-generation family history of diabetes. Identity-by-descent (IBD) analysis revealed that the four individuals represent two sib-pairs that are third-degree relatives. A novel missense mutation (p.P81S) in the PAX6 gene was one of eight rare coding variants across the genome shared IBD by all individuals and was inherited from affected mothers in both sib-pairs. The mutation affects a highly conserved amino acid located in the paired-domain of PAX6 - a hotspot for missense mutations that cause aniridia and other eye abnormalities. However, no eye-related phenotype was observed in any individual. The well-established functional role of PAX6 in glucose-induced insulin secretion and the co-segregation of diabetes in families with aniridia provide compelling support for the pathogenicity of this mutation for diabetes. The mutation could be classified as "likely pathogenic" with a posterior probability of 0.975 according to the ACMG/AMP guidelines. This is the first PAX6 missense mutation that is likely pathogenic for autosomal-dominant adult-onset diabetes without eye abnormalities.

C.487C>T mutation in PAX4 gene causes MODY9: A case report and literature review

RATIONALE

Maturity-onset diabetes of the young (MODY) is a group of autosomal dominant monogenic diabetes mellitus with a wide range of clinical manifestations that require distinct treatment strategies. MODY9 (OMIM # 612225) is a rare type of MODY, caused by a mutation in the Paired box gene 4 (PAX4).

PATIENT CONCERN

A 19-months boy was admitted to the department of endocrinology at Beijing Children's Hospital due to excessive water drinking, polyuria for over half a month, and wheezing for 3 days.

DIAGNOSE

The whole-exon sequencing analysis demonstrated that the child carried the heterozygous missense mutation of c.487>T in the 7th exon region of PAX4 gene and diagnosed MODY9.

INTERVENTION

The patient was treated with fluid therapy, ketosis correction, insulin, and anti-infection treatment.

OUTCOMES

After 17 days in the hospital, the blood glucose levels remained stable and the patient was discharged.

LESSONS

In Chinese children, the heterozygous mutation of c.487C>T in the PAX4 gene can lead to the occurrence of MODY9.Gene sequencing analysis is of great significance in the diagnosis and classification of MODY.

Hemoglobin A1C can differentiate subjects with GCK mutations among patients suspected to have MODY

OBJECTIVES

The aim of this study is to determine the clinical and molecular characteristics enabling differential diagnosis in a group of Turkish children clinically diagnosed with MODY and identify the cut-off value of HbA_1c, which can distinguish patients with GCK variants from young-onset type 1 and type 2 diabetes.

METHODS

The study included 49 patients from 48 unrelated families who were admitted between 2018 and 2020 with a clinical diagnosis of MODY. Clinical and laboratory characteristics of the patients at the time of the diagnosis were obtained from hospital records. Variant analysis of ten MODY genes was performed using targeted next-generation sequencing (NGS) panel and the variants were classified according to American Collage of Medical Genetics and Genomics (ACMG) Standards and Guidelines recommendations.

RESULTS

A total of 14 (28%) pathogenic/likely pathogenic variants were detected among 49 patients. 11 variants in GCK and 3 variants in HNF1A genes were found. We identified four novel variants in GCK gene. Using ROC analysis, we found that best cut-off value of HbA_1c at the time of diagnosis for predicting the subjects with a GCK variant among patients suspected to have MODY was 6.95% (sensitivity 90%, specificity 86%, AUC 0.89 [95% CI: 0.783-1]). Most of the cases without GCK variant (33/38 [86%]) had an HbA_1c value above this cutoff value. We found that among participants suspected of having MODY, family history, HbA_1c at the time of diagnosis, and not using insulin therapy were the most differentiating variables of patients with GCK variants.

CONCLUSIONS

Family history, HbA_1c at the time of diagnosis, and not receiving insulin therapy were found to be the most distinguishing variables of patients with GCK variants among subjects suspected to have MODY.

MODY probability calculator utility in individuals' selection for genetic testing: Its accuracy and performance

Introduction

MODY probability calculator (MPC) represents an easy‐to‐use tool developed by Exeter University to help clinicians prioritize which individuals should be oriented to genetic testing. We aimed to assess the utility of MPC in a Portuguese cohort with early‐onset monogenic diabetes.

Methods

This single‐centre retrospective study enrolled 132 participants submitted to genetic testing between 2015 and 2020. Automatic sequencing and, in case of initial negative results, generation sequencing were performed. MODY probability was calculated using the probability calculator available online. Positive and negative predictive values (PPV and NPV, respectively), accuracy, sensitivity and specificity of the calculator were determined for this cohort.

Results

Seventy‐three individuals were included according to inclusion criteria: 20 glucokinase (GCK‐MODY); 16 hepatocyte nuclear factor 1A (HNF1A‐MODY); 2 hepatocyte nuclear factor 4A (HNF4A‐MODY) and 35 DM individuals with no monogenic mutations found. The median probability score of MODY was significantly higher in monogenic diabetes‐positive subgroup (75.5% vs. 24.2%, p < .001). The discriminative accuracy of the calculator, as expressed by area under the curve, was 75% (95% CI: 64%–85%). In our cohort, the best cut‐off value for the MODY calculator was found to be 36%, with a PPV of 74.4%, NPV of 73.5% and corresponding sensitivity and specificity of 76.2% and 71.4%, respectively.

Conclusions

In a highly pre‐selected group of probands qualified for genetic testing, the Exeter MODY probability calculator provided a useful tool in individuals' selection for genetic testing, with good discrimination ability under an optimal probability cut‐off of 36%. Further geographical and population adjustments are warranted for general use.

Contribution of rare variants in monogenic diabetes-genes to early-onset type 2 diabetes

AIM

This study investigated whether rare, deleterious variants in monogenic diabetes-genes are associated with early-onset type 2 diabetes (T2D).

METHODS

A nested case-control study was designed from 9,712 Italian patients with T2D. Individuals with age at diabetes onset ≤35 yrs (n=300; cases) or ≥65 yrs (n=300; controls) were selected and screened for variants in 27 monogenic diabetes-genes by targeted resequencing. Rare (minor allele frequency-MAF <1%) and possibly deleterious variants were collectively tested for association with early-onset T2D. The association of a genetic risk score (GRS) based on 17 GWAS-SNPs for T2D was also tested.

RESULTS

When all rare variants were considered together, each increased the risk of early-onset T2D by 65% (allelic OR =1.64, 95% CI: 1.08-2.48, p=0.02). Effects were similar when the 600 study participants were stratified according to their place of recruitment (Central-Southern Italy, 182 cases vs. 142 controls, or Rome urban area, 118 vs. 158, p for heterogeneity=0.53). Progressively less frequent variants showed increasingly stronger effects in the risk of early-onset T2D for those with MAF <0.001% (OR=6.34, 95% CI: 1.87-22.43, p=0.003). One unit of T2D-GRS significantly increased the risk of early-onset T2D (OR 1.09, 95% CI: 1.01-1.18; p=0.02). This association was stronger among rare variants carriers as compared to non-carriers (p=0.02).

CONCLUSION

Rare variants in monogenic-diabetes genes are associated with an increased risk of early-onset T2D, and interact with common T2D susceptibility variants in shaping it. These findings might help develop prediction tools to identify individuals at high risk of developing T2D in early adulthood.

Low genetic confirmation rate in South Indian subjects with a clinical diagnosis of maturity-onset diabetes of the young (MODY) who underwent targeted next-generation sequencing for 13 genes

PURPOSE

To screen for maturity-onset diabetes of the young (MODY) variants in subjects with an early age of onset and positive family history of diabetes mellitus.

METHODS

60 subjects with onset of diabetes between 3 and 30 years of age and parental history (onset < 35 years) of diabetes were recruited after excluding autoimmune, pancreatic and syndromic forms of diabetes. Detailed pedigree chart and clinical data were recorded. MODY genetic testing (MODY 1-13) was performed and variant classification was done adhering to the ACMG guidelines.

RESULTS

Baseline characteristics of subjects were as follows: mean age of onset of diabetes 19.9 ± 7 years, mean duration of diabetes 6.3 ± 6.8 years, BMI 23.3 ± 3 kg/m² and C-peptide 1.56 ± 1.06 nmol/l. Four out of sixty (6.6%) were positive for variants classifiable as pathogenic/likely pathogenic: one patient with HNF4Ac.691C > T, (p.Arg231Trp), two with HNF 1A c.746C > A(p.Ser249Ter) and c.1340C > T(p.Pro447Leu), and one with ABCC8 c.4544C > T (p.Thr1515Met). MODY 1 and MODY 3 variants were documented in the paediatric age group (< 18 years).

CONCLUSION

A genetic diagnosis of MODY could be confirmed in only 6.6% (4/60) of patients clinically classifiable as MODY. This is less than that reported in clinically diagnosed MODY subjects of European descent. Newly published population data and more stringent criteria for assessment of pathogenicity and younger age of onset of type 2 diabetes in Indians could have contributed to the lower genetic confirmation rate. Apart from variants in the classical genes (HNF1A, HNF4A), a likely pathogenic variant in a non-classical gene (ABCC8) was noted in this study.

Gain of Function of Malate Dehydrogenase 2 and Familial Hyperglycemia

CONTEXT

Genes causing familial forms of diabetes mellitus are only partially known.

OBJECTIVE

We set out to identify the genetic cause of hyperglycemia in multigenerational families with an apparent autosomal dominant form of adult-onset diabetes not due to mutations in known monogenic diabetes genes.

METHODS

Existing whole-exome sequencing (WES) data were used to identify exonic variants segregating with diabetes in 60 families from the United States and Italy. Functional studies were carried out in vitro (transduced MIN6-K8 cells) and in vivo (Caenorhabditis elegans) to assess the diabetogenic potential of 2 variants in the malate dehydrogenase 2 (MDH2) gene linked with hyperglycemia in 2 of the families.

RESULTS

A very rare mutation (p.Arg52Cys) in MDH2 strongly segregated with hyperglycemia in 1 family from the United States. An infrequent MDH2 missense variant (p.Val160Met) also showed disease cosegregation in a family from Italy, although with reduced penetrance. In silico, both Arg52Cys and Val160Met were shown to affect MDH2 protein structure and function. In transfected HepG2 cells, both variants significantly increased MDH2 enzymatic activity, thereby decreasing the NAD+/NADH ratio-a change known to affect insulin signaling and secretion. Stable expression of human wild-type MDH2 in MIN6-K8 cell lines enhanced glucose- and GLP-1-stimulated insulin secretion. This effect was blunted by the Cys52 or Met160 substitutions. Nematodes carrying equivalent changes at the orthologous positions of the mdh-2 gene showed impaired glucose-stimulated insulin secretion.

CONCLUSION

Our findings suggest a central role of MDH2 in human glucose homeostasis and indicate that gain of function variants in this gene may be involved in the etiology of familial forms of diabetes.

Genetic variants of ABCC8 and phenotypic features in Chinese early onset diabetes

BACKGROUND

ABCC8 variants cause neonatal diabetes, maturity onset diabetes of the young (MODY), and hyperinsulinemic hypoglycemia because of activating or inactivating variants. In this study we used targeted exon sequencing to investigate genetic variants of ABCC8 and phenotypic features in Chinese patients with early onset diabetes (EOD).

METHODS

A cross-sectional study of 543 Chinese patients with EOD was recruited and the exons of them were conducted targeted sequencing. The pathogenicity of ABCC8 variants was defined according to the American College of Medical Genetics and Genomics and the Association for Molecular Pathology guideline. The phenotypes of patients owing to ABCC8 variants (ABCC8-MODY) were characterized.

RESULTS

Among the 543 participants, eight (1.5%) patients with ABCC8-MODY were identified. They harbored eight missense ABCC8 variants (p.R306C, p.E1326K, and p.R1379H, previously reported; p.R298C, p.F1176C, p.R1221W, p.K1358R, and p.I1404V) classified as likely pathogenic. Two family members with ABCC8-MODY were also confirmed. The average diagnosed age of the 10 patients was 26.8 ± 12.9 years. The majority of them had unsatisfactory glucose control, 80% of them had diabetic kidney disease, and neurological features were not observed.

CONCLUSION

Using targeted exon sequencing followed by pathogenicity analysis, we could be able to make genetic diagnoses for eight (1.5%) patients with ABCC8-MODY. The phenotype was variable with higher risk of diabetic microvascular complications. Genetic diagnosis is conducive for facilitating the personalized treatment of ABCC8-MODY.

Clinical and Genetic Characteristics of ABCC8 Nonneonatal Diabetes Mellitus: A Systematic Review

OBJECTIVES

Diabetes mellitus (DM) is a major chronic metabolic disease in the world, and the prevalence has been increasing rapidly in recent years. The channel of K_ATP plays an important role in the regulation of insulin secretion. The variants in ABCC8 gene encoding the SUR1 subunit of K_ATP could cause a variety of phenotypes, including neonatal diabetes mellitus (ABCC8-NDM) and ABCC8-induced nonneonatal diabetes mellitus (ABCC8-NNDM). Since the features of ABCC8-NNDM have not been elucidated, this study is aimed at concluding the genetic features and clinical characteristics.

METHODS

We comprehensively reviewed the literature associated with ABCC8-NNDM in the following databases: MEDLINE, PubMed, and Web of Science to investigate the features of ABCC8-NNDM.

RESULTS

Based on a comprehensive literature search, we found that 87 probands with ABCC8-NNDM carried 71 ABCC8 genetic variant alleles, 24% of whom carried inactivating variants, 24% carried activating variants, and the remaining 52% carried activating or inactivating variants. Nine of these variants were confirmed to be activating or inactivating through functional studies, while four variants (p.R370S, p.E1506K, p.R1418H, and p.R1420H) were confirmed to be inactivating. The phenotypes of ABCC8-NNDM were variable and could also present with early hyperinsulinemia followed by reduced insulin secretion, progressing to diabetes later. They had a relatively high risk of microvascular complications and low prevalence of nervous disease, which is different from ABCC8-NDM.

CONCLUSIONS

Genetic testing is essential for proper diagnosis and appropriate treatment for patients with ABCC8-NNDM. And further studies are required to determine the complex mechanism of the variants of ABCC8-NNDM.

Disentangling the heterogeneity of adulthood-onset non-autoimmune diabetes: a little closer but lot more to do

Diabetes diagnosed in adults is a highly heterogeneous disorder. It mostly consists of what is referred to as type 2 diabetes but also comprises other entities (i.e. different diseases), including latent autoimmune diabetes, late onset forms of monogenic diabetes and familial diabetes of the adulthood, which has recently been the source of new diabetogenes discovery. Notably, type 2 diabetes is itself heterogeneous as it includes subtypes with onset at the extremes of age and/or weight distributions characterized by different degree of hyperglycemia and cardiovascular risk as compared to common forms of type 2 diabetes occurring in middle-aged, overweight/obese individuals. Understanding whether these are different presentations of one, highly heterogeneous disease or separate nosological entities with different clinical trajectories and requiring different treatments is essential to effectively pursue the path of precision medicine.

Screening for monogenic diabetes in primary care

AIMS

Updates on the latest diagnostic methods and features of MODY (Maturity Onset Diabetes of the Young) and promotion of education and awareness on the subject are discussed.

METHOD

Previous recommendations were identified using PubMed and using combinations of terms including "MODY" "monogenic diabetes" "mature onset diabetes" "MODY case review". The diabetesgenes.org website and the US Monogenic Diabetes Registry (University of Colorado) were directly referenced. The remaining referenced papers were taken from peer-reviewed journals. The initial literature search occurred in January 2017 and the final search occurred in September 2018.

RESULTS

A diagnosis of MODY has implications for treatment, quality of life, management in pregnancy and research. The threshold for referral and testing varies among different ethnic groups, and depends on body mass index, family history of diabetes and associated syndromes. Novel causative genetic variations are still being discovered however testing is currently limited by low referral rates. Educational material is currently being promoted in the UK in an effort to raise awareness.

CONCLUSIONS

The benefits and implications of life altering treatment such as termination of insulin administration are significant but little can be done without appropriate identification and referral.

Maturity-Onset Diabetes of the Young (MODY) in Portugal: Novel GCK, HNFA1 and HNFA4 Mutations

Maturity-onset diabetes of the young (MODY) is a frequently misdiagnosed type of diabetes, which is characterized by early onset, autosomal dominant inheritance, and absence of insulin dependence. The most frequent subtypes are due to mutations of the GCK (MODY 2), HNF1A (MODY 3), and HNF4A (MODY 1) genes. We undertook the first multicenter genetic study of MODY in the Portuguese population. The GCK, HNF1A, and HNF4A genes were sequenced in 46 unrelated patients that had at least two of the three classical clinical criteria for MODY (age at diagnosis, family history, and clinical presentation). The functional consequences of the mutations were predicted by bioinformatics analysis. Mutations were identified in 23 (50%) families. Twelve families had mutations in the GCK gene, eight in the HNF1A gene, and three in the HNF4A gene. These included seven novel mutations (GCK c.494T>C, GCK c.563C>G, HNF1A c.1623G>A, HNF1A c.1729C>G, HNF4A c.68delG, HNF4A c.422G>C, HNF4A c.602A>C). Mutation-positive patients were younger at the time of diagnosis when compared to mutation-negative patients (14.3 vs. 23.0 years, p = 0.011). This study further expands the spectrum of known mutations associated with MODY, and may contribute to a better understanding of this type of diabetes and a more personalized clinical management of affected individuals.

From Hyper- to Hypoinsulinemia and Diabetes: Effect of KCNH6 on Insulin Secretion

Glucose-stimulated insulin secretion from islet β cells is mediated by K_ATP channels. However, the role of non-K_ATP K⁺ channels in insulin secretion is largely unknown. Here, we show that a non-K_ATP K⁺ channel, KCNH6, plays a key role in insulin secretion and glucose hemostasis in humans and mice. KCNH6 p.P235L heterozygous mutation co-separated with diabetes in a four-generation pedigree. Kcnh6 knockout (KO) or Kcnh6 p.P235L knockin (KI) mice had a phenotype characterized by changing from hypoglycemia with hyperinsulinemia to hyperglycemia with insulin deficiency. Islets from the young KO mice had increased intracellular calcium concentration and increased insulin secretion. However, islets from the adult KO mice not only had increased intracellular calcium levels but also had remarkable ER stress and apoptosis, associated with loss of β cell mass and decreased insulin secretion. Therefore, dysfunction of KCNH6 causes overstimulation of insulin secretion in the short term and β cell failure in the long term.

Targeted sequencing identifies novel variants in common and rare MODY genes

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

The genetic side of type 2 diabetes - A review

AIM

Type 2 diabetes (T2DM) is a complex disease. Interactions between genetic susceptible variants and environmental cues results in the development of this heterogenous disease. Having an understanding of the genetics of T2DM may lead to a better perspective and management of the pathogenesis contributing to T2DM.

MATERIALS AND METHODS

Published primary and secondary sources were reviewed covering the keywords "genetics + type 2 diabetes" using PubMed and Google Scholar as the main databases. Full articles were considered when the title and the abstract was found to be sufficiently related to the review's aim.

RESULTS

Various genetic aspects of T2DM were summarised including a general understanding of the heritability and heterogeneity of T2DM. Furthermore, an explanation of the different genetic modalities that can be used to identify T2DM susceptible genes was provided.

CONCLUSION

In this day and era, researchers and healthcare professionals working in the field of metabolic disorders should have an understanding of T2DM genetics. The future lies in preventive and management action plans targeting the combination of genetics and environmental risk factors for a better health outcome.

Genetic characterization of suspected MODY patients in Tunisia by targeted next-generation sequencing

AIMS

Maturity Onset Diabetes of the Young (MODY) is a monogenic form of diabetes with autosomal dominant inheritance pattern. The diagnosis of MODY and its subtypes is based on genetic testing. Our aim was investigating MODY by means of next-generation sequencing in the Tunisian population.

METHODS

We performed a targeted sequencing of 27 genes known to cause monogenic diabetes in 11 phenotypically suspected Tunisian patients. We retained genetic variants passing filters of frequency in public databases as well as their probable effects on protein structures and functions evaluated by bioinformatics prediction tools.

RESULTS

Five heterozygous variants were found in four patients. They include two mutations in HNF1A and GCK that are the causative genes of the two most prevalent MODY subtypes described in the literature. Other possible mutations, including novel frameshift and splice-site variants were identified in ABCC8 gene.

CONCLUSIONS

Our study is the first to investigate the clinical application of targeted next-generation sequencing for the diagnosis of MODY in Africa. The combination of this approach with a filtering/prioritization strategy made a step towards the identification of MODY mutations in the Tunisian population.