Molecular Genetic Study in a Cohort of Iranian Families Suspected to Maturity-Onset Diabetes of the Young, Reveals a Recurrent Mutation and a High-Risk Variant in the CEL Gene

Examining the clinical and genetic spectrum of maturity-onset diabetes of the young (MODY) in Iran

Maturity-onset diabetes of the young (MODY) is an uncommon monogenic type of diabetes mellitus. Detecting genetic variants for MODY is a necessity for precise diagnosis and treatment. The majority of MODY genetic predisposition has been documented in European populations and a lack of information is present in Iranians which leads to misdiagnosis as a consequence of defects in unknown variants. In this study, using genetic variant information of 20,002 participants from the family-based TCGS (Tehran Cardiometabolic Genetic Study) cohort, we evaluated the genetic spectrum of MODY in Iran. We concentrated on previously discovered MODY-causing genes. Genetic variants were evaluated for their pathogenicity. We discovered 6 variants that were previously reported in the ClinVar as pathogenic/likely pathogenic (P/LP) for MODY in 45 participants from 24 families (INS in 21 cases, GCK in 13, HNF1B in 8, HNF4A, HNF1A, and CEL in 1 case). One potential MODY variant with Uncertain Risk Allele in ClinVar classification was also identified, which showed complete disease penetrance (100%) in four subjects from one family. This is the first family-based study to define the genetic spectrum and estimate the prevalence of MODY in Iran. The discovered variants need to be investigated by additional studies.

Study of the frequency and clinical features of maturity-onset diabetes in the young in the pediatric and adolescent diabetes population in Iran

OBJECTIVES

Maturity-onset diabetes of the young (MODY), an autosomal dominant disease, is frequently misdiagnosed as type 1 or 2 diabetes. Molecular diagnosis is essential to distinguish them. This study was done to investigate the prevalence of MODY subtypes and patients' clinical characteristics.

METHODS

A total of 43 out of 230 individuals with diabetes were selected based on the age of diagnosis >6 months, family history of diabetes, absence of marked obesity, and measurable C-peptide. Next-generation and direct SANGER sequencing was performed to screen MODY-related mutations. The variants were interpreted using the Genome Aggregation Database (genomAD), Clinical Variation (ClinVar), and pathogenicity prediction tools.

RESULTS

There were 23 males (53.5%), and the mean age at diabetes diagnosis was 6.7 ± 3.6 years. Sixteen heterozygote single nucleotide variations (SNVs) from 14 patients (14/230, 6%) were detected, frequently GCK (37.5%) and BLK (18.7%). Two novel variants were identified in HNF4A and ABCC8. Half of the detected variants were categorized as likely pathogenic. Most prediction tools predicted Ser28Cys in HNF4A as benign and Tyr123Phe in ABCC8 as a pathogenic SNV. Six cases (42.8%) with positive MODY SNVs had islet autoantibodies. At diagnosis, age, HbA_1c, and C-peptide level were similar between SNV-positive and negative patients.

CONCLUSIONS

This is the first study investigating 14 variants of MODY in Iran. The results recommend genetic screening for MODY in individuals with unusual type 1 or 2 diabetes even without family history. Treatment modifies depending on the type of patients' MODY and is associated with the quality of life.

Precision Diagnosis of Maturity-Onset Diabetes of the Young with Next-Generation Sequencing: Findings from the MODY-IST Study in Adult Patients

Maturity-onset diabetes of the young (MODY) is a highly heterogeneous group of monogenic and nonautoimmune diseases. Misdiagnosis of MODY is a widespread problem and about 5% of patients with type 2 diabetes mellitus and nearly 10% with type 1 diabetes mellitus may actually have MODY. Using next-generation DNA sequencing (NGS) to facilitate accurate diagnosis of MODY, this study investigated mutations in 13 MODY genes (HNF4A, GCK, HNF1A, PDX1, HNF1B, NEUROD1, KLF11, CEL, PAX4, INS, BLK, ABCC8, and KCNJ11). In addition, we comprehensively investigated the clinical phenotypic effects of the genetic variations identified. Fifty-one adult patients with suspected MODY and 64 healthy controls participated in the study. We identified 7 novel and 10 known missense mutations localized in PDX1, HNF1B, KLF11, CEL, BLK, and ABCC8 genes in 29.4% of the patient sample. Importantly, we report several mutations that were classified as "deleterious" as well as those predicted as "benign." Notably, the ABCC8 p.R1103Q, ABCC8 p.V421I, CEL I336T, CEL p.N493H, BLK p.L503P, HNF1B p.S362P, and PDX1 p.E69A mutations were identified for the first time as causative variants for MODY. More aggressive clinical features were observed in three patients with double- and triple-heterozygosity of PDX1-KLF11 (p.E69A/p.S182R), CEL-ABCC8-KCNJ11 (p.I336, p.G157R/p.R1103Q/p.A157A), and HNF1B-KLF11 (p.S362P/p.P261L). Interestingly, the clinical effects of the BLK mutations appear to be exacerbated in the presence of obesity. In conclusion, NGS analyses of the adult patients with suspected MODY appear to be informative in a clinical context. These findings warrant further clinical diagnostic research and development in different world populations suffering from diabetes with genetic underpinnings.