The c.3102T>G (p.Tyr1034Ter) variant in ATM is a nonsense variant predicted to cause a premature stop codon in a biologically-relevant-exon leading to nonsense mediated decay in a gene in which loss-of-function is an established disease mechanism. This alteration results in a termination codon upstream of the most C-terminal pathogenic alteration (ATM p.Arg3047*), as classified by the HBOP VCEP, and is expected to be more deleterious. This variant is absent from gnomAD v.2.1.1. This variant has been detected in at least 4 individuals with Ataxia-Telangiectasia (PMID: 26896183, 18321536, 33547824). In summary, this variant meets criteria to be classified as pathogenic for autosomal dominant hereditary breast cancer and autosomal recessive Ataxia-Telangiectasia based on the ACMG/AMP criteria applied, as specified by the HBOP VCEP. (PVS1, PM3_strong, PM2_Supporting , PM5_Supporting)