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Hemochromatosis

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HEMOCHROMATOSIS

Genetics of Hemochromatosis

By definition, hereditary hemochromatosis — an iron overload disorder — runs in families: A person develops the condition by inheriting mutated copies of the HFE gene from his or her parents. The HFE gene regulates iron absorption in our bodies.

Even though this disorder is clearly inherited, it's not always easy to spot a pattern of disease within families who have the mutation. This is because people can be carriers of a hemochromatosis mutation without having any symptoms or complications.

Thus, the fact that no one in your immediate or extended family has symptoms of hereditary hemochromatosis does not mean you cannot develop it yourself. Fortunately, it's relatively easy to find out whether you have the disorder and then treat it — if it is caught early.

How Hemochromatosis Runs in Families
Different Risk for Different People

How Hemochromatosis Runs in Families

Approximately 1 out of every 9 or 10 people in the U.S. is a carrier of one of the genetic mutations that cause hereditary hemochromatosis. However, not nearly that many people actually develop symptoms or complications from the disorder.

This is because hereditary hemochromatosis is passed through families in what is known as autosomal recessive fashion, which means that an individual must inherit a mutated copy of the HFE gene from both parents to develop the disorder.

Like most genes, the HFE gene comes in pairs, with one copy inherited from each parent. Thus, if both parents have a mutation in just one of their two HFE genes, each of their children has a 25 percent chance of inheriting two mutated HFE genes — and with them hereditary hemochromatosis.

Some people who have inherited just one HFE gene with the C282Y mutation may be at risk for cardiovascular disease due to the small increases in iron storage it causes.

According to recent preliminary studies, men who carry the C282Y mutation are twice as likely to have heart attacks as men who do not have the mutation. Women who carry the C282Y mutation are one-and-a-half times more likely to have heart attacks. (Remember: You only need to have one mutated copy of the HFE gene to be a carrier.) However, more research is needed to determine if the effect is real.

People who have inherited only one HFE mutation are still at increased risk of developing hemochromatosis. This is because there are other mutations in the HFE gene that current testing does not identify. If a person inherits one of these rare mutations in combination with another mutation, they may develop symptoms of hereditary hemochromatosis.

Different Risk for Different People

To further complicate matters, even people who have inherited two mutated copies of the HFE gene have varying degrees of risk for hemochromatosis. This is because there are three distinct mutations — C282Y, H63D, and S65C — that can lead to the disorder. (The mutations are named for their location in the HFE gene)

The combination of these mutations determines both the chances of symptoms occurring and their severity. For example, the C282Y mutation appears to cause a more severe form of hemochromatosis, and one that appears at an earlier age, than the H63D or S65C mutations. Thus, people who have two copies of the C282Y mutation can develop symptoms (and, if left untreated, complications) of hemochromatosis.

People who have inherited any other combination of two HFE mutations are less likely to develop symptoms — the specific risk depends on the combination.