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Hemochromatosis

Incomplete penetrance

08/15/2005

Question:

I have been genetically tested for the trait. I am homozygous. My ferritin level is 70 and I have no symptoms. Why? I am 58 years old. I have always eaten an iron-rich diet. I have had no mestrual period for about 3 years.

Answer:

Hereditary Hemochromatosis is a genetic condition that can display what is called "incomplete penetrance." Incomplete penetrance means that not all individuals who have two gene mutations will go on to develop symptoms. Currently, with hereditary hemochromatosis, we are not able to determine who will and who will not go on to develop increased iron levels, and the symptoms that follow. We also cannot predict the age at which a person will develop increased iron levels. Therefore, it is important to have your ferritin and transferrin saturation levels screened by your physician on a regular basis, although they may be normal currently.

The most common HFE gene mutation found upon testing is the C282Y mutation. Studies have shown that a person who has two copies of the C282Y mutation is more likely to develop symptoms of iron overload (unless treated appropriately). Gender and environmental agents, such as alcohol and dietary iron, can influence the severity of disease in homozygous individuals. A smaller percentage of patients with hemochromatosis have the C282Y mutation in one copy of the HFE gene and H63D in the other copy; an even smaller percentage of patients have two copies of the H63D mutation. In both of these cases, iron overload typically occurs to a lesser degree. The severity is thus determined by an interaction between the mutation type and modifying factors.

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Response by:

Amy Curry Sturm, MS, LGC Amy Curry Sturm, MS, LGC
Associate Professor of Human Genetics
College of Medicine
The Ohio State University