Death Rates of People Who Carry the Gene for Ataxia-Telangiectasia

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The summary below is from the full report titled "Mortality Rates among Carriers of Ataxia-Telangiectasia Mutant Alleles." It is in the 21 November 2000 issue of Annals of Internal Medicine (volume 133, pages 770-778). The authors are Y Su and M Swift.

What is the problem and what is known about it so far?

Ataxia-telangiectasia is an inherited disease. People with this disease begin having problems with balance and walking during early childhood. Later, they develop skin abnormalities, frequent respiratory infections, and high rates of cancer (especially leukemia and lymphoma). To have the disease, a person needs to inherit two copies of the abnormal gene, one from each parent. Relatives of patients with ataxia-telangiectasia can be "carriers" of the abnormal gene. Carriers have only one copy of the abnormal gene. Previous studies have shown that carriers of the ataxia-telangiectasia gene have a higher risk for cancer and, possibly, heart disease than persons who do not carry this gene. It is estimated that up to 2 out of every 100 people in the United States are "carriers" of an ataxia-telangiectasia gene. However, it is unknown whether persons who carry this gene actually have higher death rates than noncarriers.

Why did the researchers do this particular study?

To find out whether persons who carry one copy of the abnormal gene for ataxia-telangiectasia have higher death rates than the general population.

Who was studied?

The study included 405 grandparents of persons with ataxia-telangiectasia.

How was the study done?

The researchers tested the grandparents to determine who carried one abnormal copy of the gene. For grandparents from whom no blood or tissue was available and for those who had died before the start of the study, the researchers determined whether they were carriers by tracking the genetic patterns of the other family members. After determining which grandparents were carriers, the researchers compared the ages at death and the risk for death from all causes, cancer, and heart disease in grandparents who did and those who did not carry the abnormal gene.

What did the researchers find?

Compared with grandparents who did not carry the gene, carriers had almost twice the risk for death between ages 20 and 79. Carriers died, on average, 7 to 8 years earlier than noncarriers. Most of the extra deaths in carriers were due to cancer or heart disease.

What were the limitations of the study?

This study did not explain why being a carrier of the ataxia-telangiectasia gene puts someone at higher risk for death from cancer or heart disease. In addition, the researchers used death certificates to establish the cause of death. Because death certificates have been shown to overestimate heart disease as the cause of death, this study's findings about heart disease may be less reliable than those about cancer.

What are the implications of the study?

Since people who carry the ataxia-telangiectasia gene die earlier, mostly because of cancer and heart disease, it might be appropriate to target them for special programs for these diseases.