Definition & Genetics
- Extremely rare, autosomal recessive disorder of iron absorption and trafficking.
- Accounts for <1% of iron-deficiency anemia (IDA) cases.
- Caused by pathogenic variants in the TMPRSS6 gene.
- Usually identified in childhood.
Pathophysiology
- TMPRSS6 gene encodes transmembrane protease, serine 6 (also known as matriptase-2).
- Matriptase-2 normally inhibits signaling pathways that activate hepcidin (the primary iron regulatory hormone).
- Loss-of-function TMPRSS6 mutation leads to uninhibited, constitutively high hepcidin levels.
- Excess hepcidin binds to ferroportin (cellular iron exporter) on enterocytes and macrophages.
- Promotes internalization and lysosomal degradation of ferroportin.
- Results in dual defect: impaired intestinal iron absorption and defective iron release from reticuloendothelial macrophages into plasma.
Laboratory Investigations
- Diagnosis suspected in microcytic anemia refractory to adequate oral iron trial.
- Final confirmation requires genetic sequencing of the TMPRSS6 gene.
| Parameter | Finding in IRIDA |
|---|---|
| Red Cell Indices | Striking microcytosis; hypochromic anemia. |
| Transferrin Saturation | Extremely low. |
| Serum Ferritin | Normal or borderline-low. |
| Serum Hepcidin | Inappropriately high (diagnostic hallmark). |
Differential Diagnosis
Before considering IRIDA, common causes of oral iron resistance must be excluded (poor adherence, ongoing gastrointestinal bleeding, underlying celiac disease).
| Differential Diagnosis | Distinguishing Features |
|---|---|
| Anemia of Chronic Disease (ACD) | Acquired hepcidin elevation via inflammatory stimuli (e.g., IL-6). Retains normal/high iron stores. Ferritin usually elevated. |
| Castleman Disease | IL-6 overproduction causes acquired hepcidin elevation. |
| Autoimmune Gastritis | Impaired iron absorption due to achlorhydria. Anti-parietal cell antibodies present. |
| KCNQ1 Germline Variants | Defective gastric acid secretion impairing iron absorption. |
| Atransferrinemia / Aceruloplasminemia | Other rare inherited defects of iron recycling. Distinct genetic testing (TF or CP genes). Aceruloplasminemia features elevated ferritin and liver iron. |
Management
Oral Iron Therapy
- Lacks significant therapeutic role.
- Fails to correct anemia due to hepcidin-mediated intestinal block.
- Isolated case reports suggest partial hematologic response utilizing ascorbic acid combined with oral ferrous sulfate.
Parenteral (Intravenous) Iron Therapy
- Required therapeutic modality to bypass intestinal absorption block.
- Response Characteristics: Hematologic response typically slow and incomplete.
- Mechanism of Incomplete Response: High hepcidin levels persistently trap infused iron within reticuloendothelial macrophages, limiting export to circulating transferrin for erythropoiesis.
- Dosing: Optimal formulation and dosing not universally established due to disease rarity.
Treatment Complications & Monitoring
- Parenteral iron administration increases serum ferritin levels in a dose-dependent manner.
- Raises clinical concern for iron overload.
- Iron loading pattern typically reticuloendothelial rather than parenchymal (differentiating it from primary hemochromatosis).
Ineffective Therapies
- Recombinant erythropoietin (EPO) administration produces no significant clinical benefit.**