Genetics and Cancer - Ataxia Telangiectasia (A-T)

There are mutations in some genes that potentially give a small predisposition to develop breast cancer. One example is ataxia telangiectasia (A-T). The risk for breast cancer may be increased for carriers of the A-T gene. Ataxia telangiectasia is a rare childhood disease that affects the nervous system and other body systems. A diagnosis of A-T is made when the following characteristics are present (symptoms often start by age 10):

• poor balance and slurred speech

• ataxia (lack of muscle control leading to an awkward gait when walking)

• telangiectasias (tiny, red "spider" veins) in the corners of the eyes or surfaces of the ears and cheeks (soon after the onset of ataxia)

Other symptoms of A -T include:

• weak immune system

• increased risk of leukemia

• increased risk of lymphoma

• extreme sensitivity to ionizing radiation (for instance, radiation from x-rays)

Ataxia telangiectasia is caused by mutations in a gene on chromosome 11 known as the ATM gene, which is involved in cell cycle control. This neurodegenerative disorder is inherited in an autosomal recessive fashion, which means that two mutated ATM genes are necessary to produce the condition - one inherited from each parent. Persons with only one ATM mutation are referred to as "carriers."

Some studies suggest that persons who are carriers of an ATM mutation are at an increased risk to develop breast cancer. It is estimated that about 1 percent of the US population, or about 2.5 million people, may be carriers for an ATM mutation. This may lead one to believe that many people with breast cancer develop it because of an ATM mutation. When breast cancer patients are studied, however, they do not have an excess of ATM mutations as compared with persons without breast cancer. Therefore, the association between ATM mutations and breast cancer risk remains unclear. Studies are being done to better understand this possible link.