Genetic haemochromatosis (GH) is a genetic disorder causing the body to absorb an excessive amount of iron from the diet: the iron is then deposited in various organs, mainly the liver, but also the heart, endocrine glands such as the pancreas, and joints. This is iron overload.
This short introductory video will help if you are new to GH.
Iron is stored in the marrow normally, but any excess is transported to the liver and then the other organs. Usually the liver stores a small amount of iron for the essential purpose of providing new red blood cells with iron (vital for health), however when excessive quantities of iron are stored in the liver it becomes damaged. Deposits of iron may also occur in other organs and joints, again causing damage.
For a long time it was believed that the disorder was rare, so GH was seldom considered as a possible diagnosis. However, recent surveys of people of Northern European origin have shown a prevalence of the gene flaws that can lead to iron overload in the order of 1 in 150*. These people are much more likely to be at risk of develop haemochromatosis, thus GH is now recognised as being one of the most common genetic disorders.
Iron overload as a result of haemochromatosis comes about because the body continually absorbs more iron from the diet than it needs. The body is then unable to rid itself of the excess, which slowly builds up over a number of years and damages the organs where it is stored. In HFE (Type 1) haemochromatosis it is rare for iron to build up to a damaging level in childhood, and in fact it often does not happen for several decades. Children can however overload iron as a result of Type 2 (Juvenile) haemochromatosis.
The underlying cause is the inheritance of a mutated gene. The faulty gene stops the normal body iron control working properly. A faulty gene, and therefore haemochromatosis, can only be inherited. Haemochromatosis cannot be “caught” from somebody else.
Although haemochromatosis is closely associated with one particular gene mutation, not everybody who has inherited that gene mutation will develop iron overload; indeed the proportion of people that do so may be quite small. Other factors must be involved, but it is not yet known what they are. The proportion of people with the gene flaws who go on to develop iron overload is called penetrance. There is uncertainty as to what this might be on average or what other factors play a part.
A normal man has about 4 grams (g) of iron in his body and a normal woman about 3.5g, mostly found in haemoglobin in the red cells of the blood. Up to 1g is stored in the tissues and may be used to make new haemoglobin if required. With haemochromatosis it is this amount stored in the tissues, the storage iron, which becomes excessive. Overload is said to occur in individuals when their stored iron rises to 5g or more; it may rise to 40g.
*Figures updated September 2019