As babies develop, their skull needs to get bigger to give the developing brain enough space to grow. We study craniosynostosis, a serious condition (affecting ~1/2,000 children) that occurs when one or more gaps between the skull bones (cranial sutures) fuses too early. Here, we used high throughput DNA sequencing technologies in more than 1,600 patients without a genetic diagnosis, to pinpoint rare alterations in the SIX1 gene; these were previously known to cause facial and hearing disorders, but not craniosynostosis. Our work highlights the importance of SIX1 in cranial suture development, and supports the addition of SIX1 to diagnostic gene testing panels for craniosynostosis. (By Eduardo Calpena, https://jmg.bmj.com/content/early/2021/01/12/jmedgenet-2020-107459 )