Sideroblastic anemia: functional study of two novel missense mutations in ALAS2.

BACKGROUND: X-linked sideroblastic anemia (XLSA) is a disorder characterized by decreased heme synthesis and mitochondrial iron overload with ringed sideroblasts in bone marrow. XLSA is caused by mutations in the erythroid-specific gene coding 5-aminolevulinate synthase (ALAS2). Anemia in XLSA is extremely variable, characteristically microcytic and hypochromic with poikilocytosis, and the red blood cell distribution width is increased and prominent dimorphism of the red cell population. Anemia in XLSA patients responds variably to supplementation with pyridoxine. METHODS AND RESULTS: We report four patients with XLSA and three mutations in ALAS2: c.611G>A (p.Arg204Gln), c.1218G>T (p.Leu406Phe) and c.1499A>G (p.Tyr500Cys). The in silico predictions of three ALAS2 mutations and the functional consequences of two ALAS2 mutations were assessed. We performed in silico analysis of these mutations using ten different softwares, and all of them predicted that the p.Tyr500Cys mutation was deleterious. The in vitro prokaryotic expression showed that the p.Leu406Phe and p.Tyr500Cys mutations reduced the ALAS2 specific activity (SA) to 14% and 7% of the control value, respectively. CONCLUSION: In view of the results obtained in this study, a clear relationship between genotype and phenotype cannot be established; clinical variability or severity of anemia may be influenced by allelic variants in other genes or transcription factors and environmental conditions.

Microcytic anemia in a pregnant woman: beyond iron deficiency.

Sideroblastic anemias are a heterogeneous group of disorders characterized by anemia of varying severity and the presence of ringed sideroblasts in bone marrow. The most common form of inherited sideroblastic anemia is X-linked sideroblastic anemia (XLSA). In many XLSA patients, anemia responds variably to supplementation with pyridoxine (vitamin B6). We describe the case of a pregnant female with XLSA who had a novel mutation on the ALAS2 gene (c.1218G > T, p.Leu406Phe). Oral chelation therapy was contraindicated and high-dose vitamin B6 would have possible side effects in pregnancy. Serum hepcidin level was very low, indicating increased absorption of iron secondary to ineffective erythropoiesis. Therapy was begun with a low dose of pyridoxine that was increased post-partum. The patient's liver showed moderate iron deposits. During a subsequent 3-month period of pyridoxine supplementation, serum ferritin level and transferrin saturation decreased, hemoglobin content and serum hepcidin level normalized, and morphologic red cell abnormalities improved markedly. The patient responded well to treatment, showing the pyridoxine responsiveness of this novel ALAS2 mutation. The baby girl had the same mutation heterozygously, and although she was neither anemic nor showed abnormalities in a peripheral blood smear, she had a mild increment in RDW and her condition is now being followed.