IDENTIFICATION OF A HIGHLY POLYMORPHIC MARKER WITHIN INTRON 7 OF THE ALAS2 GENE AND SUGGESTION OF AT LEAST 2 LOCI FOR X-LINKED SIDEROBLASTIC ANEMIA

We have identified a compound dinucleotide repeat within intron 7 of the human erythroid 5-aminolevulinate synthase (ALAS2) gene with a minimum of 9 alleles and heterozygosity of 78%. ALAS2 was placed on the multipoint linkage map of the X chromosome in the pericentromeric region with the locus order: pter-(DXS255, TFE3, DXS146)-(DXS14, ALAS2, DXZ1)-AR-(DXS153, DXS159)-qter. No recombination was observed between ALAS2 and the centromere marker DXZ1. As ALAS2 has recently been shown to be the defective locus in X-linked pyridoxine-responsive sideroblastic anemia (PRSA), the ALAS2 marker has allowed placement of the gene for PRSA into the multipoint linkage map of the X chromosome. With the previous exclusion of close linkage between DXS]4 and sideroblastic anemia with ataxia, our data show that there are at least two loci for X-linked sideroblastic anemia.