Biallelic pathogenic variants (in homozygosity or compound heterozygosity) in the ATM gene (Ataxia Telangiectasia Mutated; MIM *607585) cause Ataxia Telangiectasia (MIM #208900), an autosomal recessive condition characterized by cerebellar ataxia, immunodeficiency, skin and mucosal telangiectasias, radiosensitivity, and susceptibility to leukemia and lymphoma [17]. The gene discussed is ATM; the disease is cerebellar ataxia.