In Northern Europe familial clustering is seen in 10-20% of gastric cancer patients. In fewer than 3% a pathogenic variant in CDH1, the most important gene involved in hereditary gastric cancer, is detected. The majority of gastric cancer families remain genetically unexplained. We have sequenced a large cohort of unexplained familial gastric cancer patients for mutations in three recently described possible predisposition genes: CTNNA1, MAP3K6 and MYD88. Our data support that mutations in CTNNA1, but not MAP3K6, are a rare cause of gastric cancer susceptibility. No additional MYD88 mutations were detected suggesting that these are at most very rarely involved. (http://jmg.bmj.com/content/early/2018/01/12/jmedgenet-2017-104962 )