Most of the XLSA-associated mutations in ALAS2 are missense substitutions resulting in loss of functionality [20, 67, 69, 77, 78], whereas mutations in the ALAS2 regulatory region, such as the promoter [79] and intron 1 [8, 9, 80], lead to decreased ALAS2 expression. The gene discussed is ALAS2; the disease is X-linked sideroblastic anemia 1.