XLSA is due to loss of function mutations in the ALAS2 gene (Bergmann et al., 2010; Ducamp et al., 2011) or mutations in an enhancer of ALAS2 gene that cause the disruption of a GATA binding site important for its transcriptional regulation (Kaneko et al., 2013). The gene discussed is ALAS2; the disease is X-linked sideroblastic anemia 1.