Congenital sideroblastic anemia (CSA) is most frequently caused by X-linked mutations in ALAS2 (Delta-aminolevulinate synthase 2, XLSA), followed by ABCB7 (ATP Binding Cassette Subfamily B Member 7), SLC25A28 (Solute Carrier Family 25 Member 28) and GLRX5 (Glutaredoxin 5). This evidence concerns the gene ALAS2 and chromosome-type aberration frequency.