The Ataxia Telangiectasia Mutated (ATM) has been originally identified as the product of a gene defective in a rare genetic disorder named Ataxia Telangiectasia (A-T), characterized among other features, by progressive cerebellar neurodegeneration leading to ataxia, dysfunctions of the immune system and higher incidence of lymphoma and leukaemia development. This evidence concerns the gene ATM and ataxia telangiectasia.