The following lists possible gene combinations for the HFE gene:
- Two copies of C282Y or a copy of C282Y together with a copy of H63D or S55C mutant genes places a person at the highest risk for HH.
- Two copies of H63D, S55C, or one copy each of H63D and S55C puts a person in the low risk category and is only rarely associated with HH.
- A single copy of C282Y, H63D or S65C means that the person is a carrier. Carriers do not develop the disease, but they can pass it on to their offspring if they have children with someone who is also a carrier.
Of course, other genes besides the HFE gene can affect a person's ability to metabolize iron, so no combination of genes guarantees that someone will or will not develop the disease. For example, it is estimated that only about 25% of men and about 1% of women who have two copies of the C282Y mutation will ever develop organ damage related to excess iron.
HH affects more men than women, and symptoms of the disorder emerge at an earlier age for men, typically at about 30 to 50 years old. Two other rare forms of inherited hemochromatosis, neonatal and juvenile hemochromatosis, can cause severe iron overload in children and young adults. These disorders are caused by mutations in a different gene, one called hemojuvelin. In fact, a small percentage of cases of HH are due to mutations in genes coding for other proteins, including hemojuvelin as well as transferrin-receptor 2, ferroportin and hepcidin. Tests for these mutations are not widely available, however.