Hereditary haemochromatosis

Haemochromatosis is one the commonest inheritable genetic defects especially in people of northern European extraction. About 1:100 people carry the gene (check on this figure). There are two main genotypes (... and ...) ... is more serious and the greatest risk of haemochromatosis is for people with two copies of the abnormal gene. People with single copies are essentially normal. People with a copy of the ... gene and the ... gene have a slight risk of haemochromatosis.

Even if you have both copies of the abnormal gene the risk of actual clinical haemochromatosis is still quite low (about ...). This is called incomplete penetrance.

People with the abnormal genes do not reduce there 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 strarts to get stored as a breakdown product of ferritin called haemosiderin and this is toxix to tissue.