The correlation of a Thr92Ala polymorphism in the DIO2 gene, encoding protein D2, with altered glycemic control, obesity and type 2 diabetes mellitus (T2DM) (14–16), as well as the association of genetic variants of the DIO1 gene, encoding protein D1, with insulin resistance (17), reinforces the clinical relevance of the peripheral T4-to-T3 conversion in metabolic control. This evidence concerns the gene DIO2 and type 2 diabetes mellitus.