HFE Hereditary Haemochromatosis - Pathophysiology

Pathophysiology

Since the regulation of iron metabolism is still poorly understood, a clear model of how haemochromatosis operates is still not available. A working model describes the defect in the HFE gene, where a mutation puts the intestinal absorption of iron into overdrive. Normally, HFE facilitates the binding of transferrin, which is iron's carrier protein in the blood. Transferrin levels are typically elevated at times of iron depletion (low ferritin stimulates the release of transferrin from the liver). When transferrin is high, HFE works to increase the intestinal release of iron into the blood. When HFE is mutated, the intestines perpetually interpret a strong transferrin signal as if the body were deficient in iron. This leads to maximal iron absorption from ingested foods and iron overload in the tissues. However, HFE is only part of the story, since many patients with mutated HFE do not manifest clinical iron overload, and some patients with iron overload have a normal HFE genotype. A possible explanation is the fact that HFE normally plays a role in the production of hepcidin in the liver, a function that is impaired in HFE mutations.

People with abnormal iron regulatory genes do not reduce their absorption of iron in response to increased iron levels in the body. Thus the iron stores of the body increase. As they increase, the iron which is initially stored as ferritin is deposited in organs as haemosiderin and this is toxic to tissue, probably at least partially by inducing oxidative stress. Iron is a pro-oxidant. Thus, haemochromatosis shares common symptomology (e.g., cirrhosis and dyskinetic symptoms) with other "pro-oxidant" diseases such as Wilson's disease, chronic manganese poisoning, and hyperuricaemic syndrome in Dalmatian dogs. The latter also experience "bronzing".