Fetus triploidy is a common cause of early miscarriages. In some cases, genetic predisposition has been suspected, but the genes involved are unknown. Here we explored the genetic cause of recurrent pregnancy loss associated with fetus triploidy in an Iranian family. We found a mutation in the cyclin B3 gene that is normally required to complete meiosis in oocytes. The mutation affects chromosome segregation, resulting in abnormal oocytes and fetus triploidy. Our results implicate a rationale for testing the cyclin B3 gene in recurrent pregnancy loss. (By Dr. Andrea Riccio, https://jmg.bmj.com/content/early/2020/09/16/jmedgenet-2020-106909 )