Hereditary diffuse gastric cancer (HDGC) is a rare hereditary disease of gastric cancer caused by germline variants in the CDH1 gene. In our study of 121 Chinese patients with gastric cancer, we identified three individuals carrying CDH1 mutations. Two of them also presented with congenital tooth agenesis, a feature rarely documented in HDGC, particularly in East Asian populations. This observation suggests that developmental traits such as missing teeth may provide unexpected clues for the early recognition of CDH1 germline mutation carriers at risk, supporting timely genetic testing, counselling, and surveillance. (By Dr Lin Dong, https://jmg.bmj.com/content/early/2025/10/22/jmg-2025-111081 )