The c.875C>T variant in ATM is a missense variant predicted to cause substitution of proline by leucine at amino acid 292 (p.Pro292Leu). This variant has been detected in at least 3 individuals with Ataxia-Telangiectasia (PMID: 18634022, 30549301, 26896183). The highest population minor allele frequency in gnomAD v2.1.1 is 0.005% (1/19890 alleles) in the East Asian population (PM2_Supporting, BS1, and BA1 are not met). Experimental studies shows that this variant has impact on ATM kinase activity, protein levels and radiosensitivity was also found to be sensitive (RS<21%) when compared with wild type (PMID:18634022,19431188). The REVEL computational prediction analysis tool predicted a score of 0.752, which is above the threshold necessary to apply PP3. In summary, this variant meets criteria to be classified as likely 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. (PM3_strong, PS3_Moderate, PP3)