Heterozygous Pathogenic Nonsense Variant in the ATM Gene in a Family with Unusually High Gastric Cancer Susceptibility.

Germline pathogenic variants (PVs) in the Ataxia Telangiectasia mutated ( ATM ) gene (MIM* 607585) increase the risk for breast, pancreatic, gastric, and prostatic cancer and, to a reduced extent, ovarian and colon cancer and melanoma, with moderate penetrance and variable expressivity. We describe a family presenting early-onset gastric cancer and harboring a heterozygous pathogenic ATM variant. The proband had gastric cancer (age 45) and reported a sister deceased due to diffuse gastric cancer (age 30) and another sister who developed diffuse gastric cancer (age 52) and ovarian serous cancer. Next generation sequencing for cancer susceptibility genes ( APC , ATM , BRD1 , BRIP1 , CDH1 , CDK4 , CDKN2A , CHEK2 , EPCAM , MLH1 , MRE11 , MSH2 , MSH6 , MUTYH , NBN , PALB2 , PMS2 , PTEN , RAD50 , RAD51C , RAD51D , RECQL1 , SMAD4 , STK11 , and TP53 ) was performed. Molecular analysis identified the truncating c.5944C>T, p.(Gln1982*) variant in the ATM (NM_000051.3; NP_000042.3) in the proband. The variant had segregated in the living affected sister and in the unaffected daughter of the deceased affected sister. Familial early-onset gastric cancer is an unusual presentation for ATM -related malignancies. Individual variants may result in different specific risks. Genotype-phenotype correlations are challenging given the low penetrance and variable expressivity. Careful family history assessments are pivotal for prevention planning and are strengthened by the availability of molecular diagnoses.