ATM and ataxia telangiectasia: The gene mutated in AT, ataxia-telangiectasia mutated (ATM), is localized to chromosome 11q22.3–23.1, contains 66 exons, and encodes a 350 kDa serine/threonine kinase which phosphorylates threonine or serine residues, then phosphorylates a glutamine [1,2,3,4,5].