Prevalence of Dio2(T92A) polymorphism and its association with thyroid autoimmunity

The 3,5,3'-L-triiodothyronine (T₃) partly derives by the deiodination of the prohormone 3,5,3',5'-L-tetraiodothyronine (T₄) by the type 2 iodothyronine deiodinase (D2). The single-nucleotide polymorphism in the D2 gene at position 92 (Dio(2T92A)), generates an enzyme with a reduced T₄ to T₃ conversion velocity. Because thyroid hormones can modulate the immune response, we hypothesized a pathophysiological role for Dio(2T92A) polymorphism in autoimmunity. The objective of this study was to investigate the Dio(2T92A) polymorphism in relation to thyroid autoimmunity (TA). We compared the prevalence of Dio(2T92A) polymorphism and serum thyroid hormone levels in healthy subjects and subjects with TA. A total of 110 subjects with TA and 106 controls were genotypized for Dio(2T92A) polymorphism. Free T₃ (FT₃), free T₄ (FT₄) and TSH were measured and compared with the Dio(2T92A) polymorphism. Dio(292T/A), Dio(292A/A), and Dio(292T/T) healthy subjects were 40.9%, 46.4%, and 12.7%, respectively. These prevalences were similar to those of some European countries whilst significantly different from that of Brazil. In the two groups of healthy subjects and TA subjects, Dio(2T92A) polymorphism had a similar distribution with non-significant differences. Similarly, no significant differences were observed in the serum concentration of FT₃, FT₄, and TSH between subjects with different Dio(2T92A) polymorphism. The FT₄/FT₃, and TSH/FT₃ ratios were higher in Dio(292T/T) than in Dio(292T/A) and Dio(292A/A) subjects in both TA and healthy groups, but these differences were not significant. In conclusion, the distribution of Dio(2T92A) polymorphism may reflect geographical and ethnic differences, and it is not associated with TA.