Individuals carrying mutations in the CDH1 gene have a high likelihood of developing stomach cancer (lifetime risk 24-42%) and breast cancer (lifetime risk about 43-55%). Identification of these individuals through genetic testing is important because these cancers can be prevented by prophylactic surgery or detected early with endoscopy and breast imaging. Current guidelines recommend genetic testing when certain clinical criteria are met. These criteria are difficult to remember and apply in the real world. Using data from 112 known CDH1 mutation carriers, we show that these clinical criteria are also overly restrictive, capturing only about 20% of individuals who harbor CDH1 mutations. We then propose simpler criteria that would identify nearly 90% of CDH1 mutation carriers. (By Dr Xavier Llor, https://jmg.bmj.com/content/early/2022/01/24/jmedgenet-2021-108169 )