To the Editor: A 2-y-old boy presented with pallor at the age of 1 y, without epistaxis, dermatorrhagia or black stools. His parents are cousins. Complete blood count at the local hospital suggested hemoglobin 55 g/L. He was treated with oral ferrous succinate for 1 y. Physical examination at our outpatient clinic revealed anemic appearance. Complete blood count showed RBC 4.35×1012/L, Hb 66 g/L, HCT 25.5%, MCV 58.6 fl, MCH 15.2 pg, MCHC 259 g/L, RDW-CV 19.6%, RET% 1.98%, RET 0.0861×1012/L, WBC 5.8×109/L, PLT 530×109/L. Iron metabolic parameters showed serum iron (SI) 2.1 µmol/L, transferrin saturation (TS) 4.6%, serum ferritin (SF) 65.8 ng/ml, transferrin (Tf) 2.12 g/L, total iron binding capacity (TIBC) 46.1 µmol/L. The patient's SF level was not decreased, Tf and TIBC were not increased, in combination with the infantile onset, inbreeding of the child's parents and no response to oral iron, suggesting disorder of iron metabolism. Therefore, DNA samples of the blood were extracted for capturing target regions of disease-related genes and deep sequencing. Homozygous variant of c.1071delC (p.P357fs) was detected on the is transmembrane protease, serine 6 (TMPRSS6) gene, and his parents were heterozygous. This mutation was not recorded in gnomAD population database or HGMD database.

The child was diagnosed as Iron-refractory iron deficiency anemia (IRIDA) and received intravenous infusion of iron sucrose with one-time-dose of 250 mg every 2 mo. The hemoglobin level increased to 118 g/L four months later. MCV, MCH, MCHC, SI and TS all increased to normal.

Refractory iron deficiency anemia (IDA) should be an alert for IRIDA [1]. The pathogenic gene of IRIDA is TMPRSS6 [2]. Due to TMPRSS6 mutation and high expression of hepcidin, iron transfer in duodenum cells and macrophages was inhibited [3, 4]. Here, we report a rare case of IRIDA diagnosed in early childhood in China and find a novel pathogenic mutation site of TMPRSS6 gene. Intravenous iron infusion is the effective treatment for IRIDA.