Non HLA genetic markers association with type-1 diabetes mellitus

Abstract

The currently available data identified IDDM1 and IDDM2 as 2 susceptibility loci for type 1 diabetes (T1D). The major histocompatibility complex (MHC)/HLA region referred to as IDDM1 contains several 100 genes known to have a great influence on T1D risk. Within IDDM2, a minisatellite variable number of tandem repeats (VNTR) locus in the insulin gene (INS) promoter region is likely to represent the etiologic polymorphism. The aim of the present work was to study the association between genotypes and susceptibility to T1D among Egyptian diabetic children and their family members. Twenty-five nuclear Egyptian families with 27 children having T1D, aged 3–14 years, their non-diabetic 44 sibs, aged 3–15 years and their parents were included in our study. All studied children were subjected to: detailed history and family pedigree. Thorough clinical examination and anthropometric measurements. Laboratory work up of diabetes including random blood sugar (RBS) and HbA 1C. Molecular genetics of INS was studied in four steps; nucleic acid purification, amplification, sequencing and haplotyping using flanking single nucleotide polymorphisms (SNPs) as surrogate markers for minisatellite alleles identification. Analysis of variant repeat distribution among Egyptian families combined with flanking haplotypes revealed that all our diabetic children had class I alleles of INS; 9 had class IC+, 9 had class ID+ and 9 had class ID−, while all non-diabetic family members had class III alleles of INS. Therefore the three class I alleles were considered to be equally predisposing to T1D, while class III alleles are dominantly protective. There was significant positive correlations between body mass index (BMI) and both HbA 1C and AST liver enzyme among diabetic children with class IC+ but not other alleles; indicating that they need close monitoring of their diabetic control and liver functions beside following specific dietary regimens. It can be concluded that all class I alleles (IC+, ID+ and ID−) are equally important susceptibility factors for T1D among Egyptian children, while class III alleles (IIIA and IIIB) are dominantly protective. It is concluded also that our diabetic children with class IC+ are an especially endangered subgroup of diabetics. Genotyping for INS-VNTR alleles is recommended for diabetic children as an important step of diagnostic and follow up regimens and for their non-diabetic family members for family counseling and early identification of potential diabetics. Further studies of INS-VNTR alleles and HLA haplotypes all over Egypt are recommended to define the Egyptian susceptibility loci for T1D and their relations to the clinical and laboratory findings as an important national programs.