ALAS2 and myelodysplastic syndrome with ring sideroblasts: In addition, women with XLSA nearly always have normocytic or macrocytic anemia that has to be distinguished from MDS-RARS, they develop symptomatic XLSA later in life due to acquired skewing of X chromosome inactivation in hematopoietic cells leading to predominance of an active X which bears an ALAS2 mutation.