Genetic causes of hypochromic microcytic anemia include thalassemias and some rare inherited diseases such as DMT1 deficiency. Here, we show that iron deficiency anemia with poor intestinal absorption and defective iron utilization of IV iron is caused by inherited mutations in TMPRSS6, a liver-expressed gene that encodes a membrane-bound serine protease of previously unknown role that
IntroductionHypochromic microcytic anemia is quite common in children with poor iron intake. 1 Genetic causes include thalassemias 2 and some rare inherited forms with defective absorption and use of iron. 3,4 Recently, several groups, 5,6,7 including ours, 7 have reported genetic defects of the iron transporter DMT1 in such patients. It is noteworthy that DMT1 mutations causing microcytic anemia have been associated with rather high serum iron and transferrin saturation as well as increased hepatic iron stores. 8 Here we report the case of a young patient with microcytic iron-refractory iron deficiency anemia (IRIDA) who is a compound heterozygote for 2 nonsense mutations in the transmembrane serine protease TMPRSS6. Mutations in this gene have been recently described in the Mask mouse, a mouse model of IRIDA, 9,10 and TMPRSS6 knock-out mice also display the same phenotype. 11 Our observations confirm a very recent communication reporting germ line mutations of TMPRSS6 in IRIDA patients 12
MethodsThe proband was born to nonconsanguinous English parents and was 18 months old when microcytic hypochromic anemia was first diagnosed. He presented with rotavirus gastroenteritis and he was incidentally found to have a hemoglobin concentration of 60 g/L, mean corpuscular volume of 47 fL, and serum iron below 5 mol/L. He is one of dizygotic twins and has one elder sister. In retrospect, he was thought to be mildly symptomatic of anemia as parents felt he was more lethargic than his twin sister. Both parents are normal and he is the only affected sibling (Table 1). Serum haptoglobin concentration was normal. Thereafter, serum iron was consistently low (Ͻ 5 mol/L), transferrin saturation was less than 5%, and serum ferritin was usually in the lower normal range. Three attempts were undertaken to correct the iron deficiency with 200 mg oral iron per day for either 6 months when he was 21 months old or for 3 months at the age of 3 years and once again at the age of 6 years. He failed to respond to oral iron, with no improvement in hemoglobin levels and serum iron remaining below 5 mol/L. At the age of 7 years, iron absorption was assessed by administration of oral ferrous iron at 3 mg/kg followed by measurement of serum iron at 3 hours. Defective iron absorption was demonstrated by a rise of 13 mol/L in serum iron compared with a minimal expected rise of 18 mol/L for children with comparable IDA. 13 Consequently, he was given a course of intravenous iron (iron sucrose 100 mg weekly during 3 consecutive weeks). Serum ferritin rose from 11 g/L to 109 g/L and hemoglobin rose from 68 g/L before the treatment to a maximum of 98 g/L. Microcytosis ...