Genetic aspects of ataxia-telangiectasia.

: Ataxia-telangiectasia (A-T) is an autosomal recessive syndrome whose principal features are progressive cerebellar ataxia, oculocutaneous telangiectasia, varied immune defects, a high cancer incidence, and clinical and cellular sensitivity to ionizing radiation and certain radiomimetic compounds. Cell and chromosome complementation studies have provided some evidence that mutations leading to the A-T phenotype may have occurred at more than one locus. Mapping with DNA polymorphisms has localized the predominant A-T mutation to chromosome 11q22-23. Heterozygous carriers of an A-T allele constitute about 1% of the United States population and are at a high risk for certain cancers, most notably female breast cancer. Cloning of the A-T allele(s) will assist in the early or prenatal diagnosis of A-T and provide a firm basis for determining who, in the general population, carries this gene and is therefore at a high risk of cancer.