Germline pathogenic mutations in ATM cause ataxia-telangiectasia, a syndromic disorder characterized by progressive cerebellar ataxia, oculomotor apraxia, immunodeficiency, and an increased risk of malignancy.105 Heterozygosity for ATM loss-of-function mutations has been implicated in increased cancer susceptibility, though studies suggest that carriers of ATM pathogenic mutations do not exhibit a significantly elevated risk of contralateral breast cancer (CBC) compared to non-carriers.106. This evidence concerns the gene ATM and cerebellar ataxia.