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. The gene discussed is ATM; the disease is hereditary disease.