A rare fatal disease involving a damaged immune system, unsteady walk, premature aging, and a strong predisposition to some kinds of cancer. People who possess only one copy of the gene, called ATM, do not have the disease, but may be predisposed to cancer and unusually sensitive to radiation.

Dr. Danilo Tagle, of the National Human Genome Research Institute's Genetics and Molecular Biology Branch, defines ataxia-telangiectasia.

Related terms: cancer, gene, leukemia.