The aim of this work was to study the polymorphism in CTLA4 gene in insulin-dependent diabetes mellitus (IDDM) type I patients in Baghdad population. To achieve this goal, blood samples were collected from 80 IDDM (40 males and 40 females) and 20 samples of healthy, DNA was isolated and the CTLA4 gene (A 152 bp fragment) were amplified by using specific primers for exon1 of this gene, and then found the sequence of this region. The DNA sequencing results of flank sense of CTLA4 gene from healthy patients was found to be compatible (100%) with wild type of Homo sapiens from the Gene Bank, while 99% compatibility were found for the gene from 70 IDDM cases patients with wild type of gene. The difference may be attributed to one transition mutations, A/G at position 49 of the CTLA4 gene (from AGC to AAC). It is a missense mutation that leads to changes in amino acid from serine (S) to asparagine (N). Our results showed that the incidence of A/G mutation at nucleotide position 49 and diabetes was highly significant (X2 = 100, P < 0.01). In total, 12% of patients with IDDM (10 cases) had two transition mutation +49 A/G and +47 C/T single nucleotide polymorphism from total cases, 98% compatibility were found for that gene from 10 IDDM cases patients with wild type of gene. The +47 C/T SNP was silent mutation which resulted in change of codon from GGT to GGC but no changes translated to amino acid (glycine to glycine). However, there was no significant correlation between diabetes and incidence of C/T at nucleotide 47 (X2 = 0.055, P > 0.05). In conclusion, our case study suggests that the +49 A/G SNP of the CTLA4 gene is strongly associated with genetic susceptibility to type 1 diabetes mellitus in the Baghdad/Iraqi population.
Key words: CTLA4 gene, insulin-dependent diabetes mellitus, A/G polymorphism.
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