DUOX1 and cyclic hematopoiesis: The DUOX1 and DUOX2 proteins exhibit 83% sequence homology; however, DUOX2 is thought to be the dominant isoenzyme in the thyroid, as evidenced by its higher thyroidal expression levels and the observations that human mutations in both DUOX2 and DUOXA2, but not DUOX1, have been implicated in CH.