Although patients with XLSA are predominantly males, because of hemizygosity of the X-linked defect, many cases of female patients with the heterozygous ALAS2 mutation have also been reported (Fujiwara and Harigae, 2019), and this is usually due to an age-related skewing of X chromosome inactivation. Here, ALAS2 is linked to X-linked sideroblastic anemia 1.