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 observations that, in humans, monogenic mutations in both DUOX2 and DUOXA2, but not DUOX1 or DUOXA1, have been implicated in CH. This evidence concerns the gene DUOXA2 and cyclic hematopoiesis.