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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 one in 100 persons may be a carrier 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.