SAT-669 CD40 Ligand Gene Mutation in Type 1 Diabetes Mellitus in a Saudi Consanguineous Family

Abstract

Introduction: Type 1 Diabetes Mellitus (T1D) is a common autoimmune disorder. Investigating genetic factors that could turn the immune cells to auto-reactive are critical to our understanding of T1D. In this study genetic factors and the affected autoimmunity related molecular mechanisms in familial T1D with parental consanguinity were studied. Materials and Method: Whole Exome Sequencing (WES) was performed in a family with familial T1D. Sanger Sequencing was done to analyze segregation in affected and non-affected. Clinical and molecular aspects were also evaluated. Protein modeling and other in silico tools were used to identify probable impact of genetic abnormalities on the structure and function of protein. Result: We identified a novel homozygous substitution mutation at “c.379A>T:p.Iso127Val” in CD40 Ligand (CD40LG) gene in diabetic siblings by WES. This change was found to be segregating in the affected and non-affected individuals by Sanger sequencing. Parents and non-diabetic siblings were found to be heterozygous carriers of the nucleotide change. The c.379A>T is located within evolutionarily conserved locus of human genome. Functional prediction by Gene Ontology term analysis suggested that immune functions of CD40LG are compromised by this genetic change. Further, by protein-modeling analysis we identified that structure of ligand-binding domain of CD40LG protein, with which it interacts with other immune cells, may also be affected. In silico analysis revealed significantly reduced spatial inter amino acid distance between the site of genetic change and the ligand binding domain in mutant CD40LG. Discussion: Apoptotic elimination of developing auto-reactive T-cells, having the potential to generate an autoimmune response against pancreatic cells, is critical to prevent T1D. This apoptotic removal mechanisms, occurs in thymus and is dependent on highly specific interaction of cell surface molecules as CD40LG on developing T-cells, and the corresponding cell surface molecules on Antigen Presenting Cells (APC). In the diabetic individuals investigated in our study, the mutation in CD40LG gene, caused significant structural damage to its protein, due to which these interactions between mutant CD40LG (present on T-cells) and the corresponding CD40 (present on APC) were probably affected. This loss of interaction between CD40LG bearing T-cells and APC, probably led to escape of auto-reactive T-cells in to immune system, which further generated autoimmune response against the pancreatic tissue, precipitating to T1D among these individuals. Conclusion Genetic investigation of cell surface proteins in autoimmune cells and understanding their mechanism for development of autoimmunity offers prospects for the development of new therapeutic strategies in the approach to probable early diagnosis of T1D.

Sib-pair subgroup familial type 1 diabetes mellitus in children in the state of Qatar

“…In this study, the diagnosis of type 1 diabetes was not based on autoantibody profiling. In Saudi Arabia, a novel mutation was discovered in a Saudi family with 3 affected siblings [28] suggesting a possible genetic basis for familial type 1 diabetes. Finally, a study from Kuwait reported a familial form of type 1 diabetes in 33% of their patients with type 1 diabetes but again the diagnosis of type 1 diabetes was not based on autoantibody status [18].…”