ATM and ataxia telangiectasia: Ataxia-telangiectasia (A-T) is a pleiotropic disorder with predisposition to cancer and early onset neurodegeneration as key features.1, 2, 3 The neuropathological abnormalities in A-T include progressive loss of cerebellar Purkinje and granule neurons, less pronounced degeneration of the bulbar olivae in the brainstem and mild loss of myelinated fibers in corticospinal and spinocerebellar tracts.4 A-T is caused by germline mutations inactivating the ataxia telangiectasia mutated (ATM) protein kinase, which has an apical role in the DNA damage response (DDR) to double-strand breaks (DSBs).