Digenic hemochromatosis

Digenic hemochromatosis (Orphanet code 648581) is a rare form of hereditary hemochromatosis in which iron overload results from the combined effect of pathogenic variants in two different genes involved in iron metabolism, rather than from mutations in a single gene alone. Genes implicated in digenic hemochromatosis may include HFE, TFR2, HAMP, HJV (HFE2), and SLC40A1, among others. In this condition, carrying heterozygous or homozygous variants in two of these genes can produce a more severe or earlier-onset phenotype than would be expected from either variant alone. The synergistic interaction between the two gene defects leads to inappropriately low hepcidin levels or altered iron sensing, resulting in excessive intestinal iron absorption and progressive iron deposition in tissues. The excess iron primarily accumulates in the liver, heart, pancreas, joints, and endocrine organs. Key clinical features include liver disease (hepatomegaly, fibrosis, and potentially cirrhosis), diabetes mellitus due to pancreatic iron deposition, cardiomyopathy, arthropathy (particularly of the second and third metacarpophalangeal joints), skin hyperpigmentation (bronze discoloration), fatigue, and hypogonadism. Laboratory findings typically show elevated serum ferritin and transferrin saturation. The severity and age of onset can vary depending on the specific combination of gene variants involved, as well as environmental and lifestyle factors such as dietary iron intake and alcohol consumption. Treatment follows the same principles as other forms of hereditary hemochromatosis. Therapeutic phlebotomy (regular blood removal) is the mainstay of treatment and is effective at reducing iron stores and preventing organ damage when initiated early. In patients who cannot tolerate phlebotomy, iron chelation therapy may be considered. Monitoring of serum ferritin and transferrin saturation guides treatment frequency. Early diagnosis and treatment can prevent irreversible complications such as cirrhosis and cardiomyopathy. Genetic counseling is recommended for affected individuals and their families, given the digenic nature of the condition, which complicates recurrence risk assessment compared to classic monogenic hemochromatosis.

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