The Genetic Profile of Maturity Onset Diabetes of the Young in Sri Lanka using Next Generation Sequencing 

Background

Maturity Onset Diabetes of Young (MODY) is a monogenic type of diabetes with clinical, metabolic and genetic heterogenecity which is characterized by young onset (< 25 years) diabetes, early onset diabetes in family members, autosomal dominant inheritance and non-insulin dependence. Definitive diagnosis of MODY is vital to decide on personalized therapy and for family screening, which need genetic categorization. The estimated prevalence of MODY is about 0.8-2% [1,2,3] among diabetes patients which make it imperative to develop specific screening criteria to pick up those who are having highest pretest probability to be referred for genetic screening which is a technically demanding and expensive investigation. 

Aims

The objectives of this study are to develop specific clinical and biochemical screening criteria for MODY to refer for MODY genetic categorization. And then to utilize a Next Generation Sequencing (NGS) based strategy for MODY gene mutations analysis in a similarly selected cohort of patients for establishment of genetic mutations of MODY types in Sri Lankan population and family screening of index cases to bring about a genetic characterization to MODY patients in Sri Lanka
 
Methods

This is a cross sectional analytical study among patients with diabetes referred to the diabetic clinic National Hospital of Sri Lanka. The specific screening criteria for MODY which were used as inclusion criteria were: Onset of diabetes before 40 years of age, presence of 2 or 3 generation family history of diabetes, absence of beta cell immunity (Negative GAD antibody), no history of diabetes ketoacidosis, evidence of endogenous insulin production (detection of measurable C peptide in the presence of hyperglycemia and low Insulin requirement (<0.5u/kg/d) or lack of ketoacidosis when Insulin is omitted. Those patients who were not Sri Lankans by decent were excluded. A total number of 87 patients who fulfilled the selection criteria were included in the study.
A multiplex polymerase reaction (PCR) based target enrichment coupled Next-Generation Sequencing (NGS) based strategy was used to screen 13 known MODY genes in all 87 study subjects. The identified probable pathogenic mutations and variants were confirmed by Sanger sequencing. The NGS based testing was carried out at Christian Medical Collage, Vellore, India. Family screening in eight mutation positive index cases were carried out in the similar manner.   
 
Results

 82 patients were included in the study, 15 patients were found to be carriers of MODY related variants accounting for 18% in our sample of patients who had been screened with the strict selection criteria. 
The most common mutation in our study sample was PDX1 mutation accounting for MODY type 4 in 6 patients. There were 2 positive patients each in HNF1A (MODY 3), NEUROD1 (MODY 6) and ABCC8 (MODY 12) genes. There was one patient each with mutations in HNF4A (MODY 1), KLF11 (MODY 07) and BLK (MODY 11). 
Out of the gene panels screened, 4 were novel mutations (2 in ABCC8 gene and one each in KLF11, HNF1A and PDX1 genes). ABCC8 c.695G>A was classified as pathogenic variant according to American College of Medical Genetics and Genomics (ACMG) 2015 classification. ABCC8 c.2401G>T, HNF1A c.1135C>T and PDX1 c.98C>A were classified as likely pathogenic and KLF11 c.1120G>A as variant with uncertain significance. 
 
Discussion

This confirms that the specific criteria we have used to select patients for MODY screening has yielded a prevalence value of 18% and it can be used as future screening model. Few of the PDX1 gene variants based on the ExAC has been suggested that these variants could be benign. However, these variants are consistently very rare with a MAF <0.001 and have shown to functionally impact the normal function of the PDX1 protein. Therefore, PDX1 variants such as E224K are a strong candidates for a pathogenic variant in Sri Lankan patients. The genetic characterization of MODY patients in Sri Lanka is quite different from European population where the most common mutation is HNF 1A mutation [4] whereas in ours it is PDX1.

The genetic profile of maturity onset diabetes of the young in Sri Lanka using next generation sequencing