| Modification Notes |
DIO2 (deiodinase, iodothyronine, type II), also known as D2, 5DII, SelY, TXDI2 or ITDI2, is a 273 amino acid single-pass selenoprotein that belongs to the iodothyronine deiodinase family and localizes to the membrane. Expressed in muscle, heart, brain, thyroid, placenta and skeletal muscle, DIO2 functions to activate thyroid hormone (TH) by catalyzing the outer ring deiodination of the prohormone thyroxine (T4) to bioactive 3,3',5-triiodothyronine (T3), a reaction that is essential for providing the appropriate levels of T3 during brain development. Overexpression of DIO2 is associated with an increase in thyroidal T3 production in patients with Graves disease and thyroid adenomas, both of which are thyroid disorders. Defects in the gene encoding DIO2 may be associated with osteoarthritis, McCune-Albright syndrome and hypertension. DIO2 is expressed as two alternatively spliced isoforms, designated hDII-a and hDII-b. |