Study of Deiodinase Type 2 Polymorphisms in Graves' Disease and Ophthalmopathy in a Swedish Population

Background: Deiodinase type 2 (DIO2) is an enzyme that catalyzes the production of the active form of thyroid -hormone triiodothyronine (T3) from thyroxine (T4) and is important for maintaining intracellular T3 levels. Single nucleotide polymorphisms (SNPs) in DIO2 were associated with several diseases. The association of SNPs in DIO2 with Graves' disease (GD) was suggested in 2 Russian studies. Objectives: The aim of the study was to examine whether SNPs in DIO2 are associated with GD or Graves' ophthalmopathy (GO). Methods: Seven SNPs in the DIO2 gene - rs225014 (Thr92Ala), rs12885300, rs2267872, rs225011, rs224995, rs225015, and rs2267873 - were studied to assess their association with GD and GO. In total, 712 patients with GD with (n = 311) or without (n = 399) ophthalmopathy and 1,183 sex-matched controls from Malmö, Sweden were analyzed. In GD patients with available data, the SNPs were examined for association with the levels of free T3, free T4, thyroid-stimulating hormone receptor antibodies (TRAb), and thyroid-peroxidase antibodies (TPOAb). Results: Rs225011 was nominally associated with GD (OR 1.18, CI 1.01-1.37, p = 0.036). None of the SNPs were associated with GO. In GD patients, none of the SNPs were associated with the free-T4 (fT4), TRAb, or TPOAb levels. A weak, nonsignificant association was observed between free-T3 (fT3) levels and rs225014 and rs12885300, separately. Conclusions: Rs225011 in DIO2 was weakly associated with GD. The mechanism behind this association requires further study. None of the investigated common SNPs in DIO2 was significantly associated with GO, fT3, fT4, TRAb, or TPOAb in GD patients.