HH is a genetic disorder characterized by iron overload as a result of increased iron absorption. Between 3 - 4 mg of iron may be absorbed each day with HH, compared to 1 - 2 mg absorbed normally. As iron absorption increases, the amount of iron bound to transferrin and transported in the plasma subsequently increases.
With no available mechanism for excreting excess absorbed iron, normal iron storage sites become overloaded, resulting in ferritin levels that far exceed normal. As a result, iron is deposited in the parenchymal cells of the liver, pancreas, pituitary, heart, synovium, and other tissues with high concentrations of transferrin receptors. Iron in excess of normal cellular ferritin stores contributes to the generation of free radicals and reactive oxygen intermediates that cause cell damage to organs and tissues. This process results in the clinical condition known as iron overload, a hallmark feature of HH.
Altered iron absorption is also found in other diseases, but a comprehensive discussion is beyond the scope of this unit.