Effect of DMT1 Mutations at Birth and in the First Years of Life.

Divalent metal transporter 1 (DMT1) is involved in dietary iron uptake on the luminal side of duodenal enterocytes and transfers iron from the endosome to the cytosol in the marrow erythroblasts. Spontaneous (mk mice and Belgrade rats) or acquired (DMT1 -/- mice) inactivation of DMT1 in rodents produces a severe microcytic anemia at birth, caused by inefficient intestinal iron absorption and defective iron utilization in erythroid cells. The first reported patient with DMT1 mutations had microcytic anemia and iron overload in adult life. We here report the hematological phenotype of a newborn with a severe mycrocytic anemia (Hb 4 g/dL, MCV 71 fL) at birth and during the first months of life. Serum iron, transferrin saturation and serum ferritin were 160 microg/L, 100% and 846 ng/ml respectively at 3 months of age. Hepatic iron overload wad documented at the age of 5 years by both non invasive SQUID and liver biopsy. Sequence analysis of genomic DNA of the family revealed that the child was compound heterozygote for two novel DMT1 mutations, inherited by the asymptomatic parents. The first change deleted 3 bp (c.310 - 3_5del CTT) in intron 4 resulting in a splicing abnormality and the skipping of exon 5. The second was C>T 1246 substitution that causes arginine > cysteine replacement at position 416 (p. R416C) in the protein. This missense affects an highly conserved residue in one of the putative transmembrane domains. A striking reduction of the protein in peripheral blood cells of the proband was demonstrated by western blot using an anti-DMT1 antibody. The child required blood transfusions at birth and in the first two months of life. Thereafter, treatment with subcutaneous erythropoietin mantained hemoglobin levels between 7.5–9.5 g/dL, allowing transfusion-independence. The haematological phenotype of this patient highlights the essential role of DMT1 in erythropoiesis. The early and significant hepatic iron accumulation indicates that, as in animal models, DMT1 is dispensable for liver iron uptake. Finally DMT1 inactivation in the gut is likely bypassed by other pathways of iron absorption.