The reduced activity of ALAS2 causes an impairment of heme biosynthesis; as PPIX production is decreased, excess iron accumulates in perinuclear mitochondria of erythroblasts creating a ring-like appearance and thus the characteristic “ringed sideroblasts.” XLSA patients are characterized by hypochromic, microcytic anemia of variable severity. This evidence concerns the gene ALAS2 and X-linked sideroblastic anemia 1.