AG and GG genotypes of Exon 1 +49A/G polymorphism of CTLA4 gene when compared with AA genotype between patients and control by chi-square test-2x2 contingency table showed to increase susceptibility to autoimmune hypothyroidism (p = 0.0004 and odds ratio 5.333; p = 0.0019 and odds ratio 5.779 respectively) (Table 1). Here, CTLA4 is linked to Hashimoto thyroiditis.