We aimed to evaluate the contribution of CTNNA1 and CTNND1 germline variants to HDGC, as well as to compare the frequencies of CDH1 and CTNNA1 (and eventually CTNND1) germline variants in patients/families with DGC with those with mixed GC to evaluate the pertinence of genetic testing of these genes in the latter. The gene discussed is CTNND1; the disease is CDH1-related diffuse gastric and lobular breast cancer syndrome.