Heterogeneity and clinical relations of INS-VNTR alleles in Egyptian families of children with type i diabetes mellitus

ABSTRACT

The currently available data identified IDDMI and IDDM2 as 2 susceptibility loci for type I diabetes [T1D]. The major histocompatibility complex [MHC]/HLA region referred to as IDDMI contains several hundred 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. Susceptibility effects of the 3 classes of INS, nature of the interaction of the products of HLA and INS-VNTR, the confounding population substructure and ethnicity are still unresolved issues. The aim of the present work was to study the heterogeneity of INS-VNTR alleles among Egyptian children with T1D and their families and to evaluate the clinical findings associated with different alleles. Twenty-four nuclear Egyptian families with 26 children having TID, aged 2-16 years, and their non-diabetic family members [74] as a control group, aged 1-15 years were studied. All studied children were subjected to Detailed history and family pedigree. Thorough clinical examination and anthropometric measurements .Laboratory work up of DM including random blood sugar [RBS] and HbA[1]C. Molecular genetics of INS was studied in 4 steps; nucleic acid purification, amplification and genotyping, 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 8 had class ID-, while all non-diabetic family members had class III alleles of INS [45 had class IIIA and 29 had class IIIB]. Therefore the 3 class I alleles were considered to be equally predisposing to T1D, while the 2 class III alleles are dominantly protective. It can be assumed that IDDM2 may have a multi-locus etiological basis and that racial differences and developmental plasticity with different phenotypes from a single genotype depending on the early environment are reasonable explanations for differences in between various studies. The present work revealed a markedly high familial occurrence of T1D, mild anemia and increased frequency of urinary tract infection [UTI] among all studied diabetic children. The 3 alleles of INS-VNTR had insignificant relations to demographic, clinical and laboratory variables prevailing among Egyptian children with TID .There was significant positive correlations between body mass index [BMI] and both HbA[1]C 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 [lIlA and 1118] 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. Close monitoring and periodic assessment of diabetic control, anemia, urinary tract infection and liver function is recommended for diabetic children especially those with class IC+alleles. Further studies of INS-VNTR alleles and HLA haplotypes all over Egypt are recommended to define the Egyptian susceptibility loci for TID and their relations to the clinical and laboratory findings as an important national project