Congenital hydrocephalus is an important birth defect where there is abnormal accumulation of fluid within the brain and is often associated with abnormal neurological outcome.  Causes of isolated forms of congenital hydrocephalus are many including genetic causes but only two genes have been reported to date (L1CAM and CCDC88C).  In this study, the authors add a third gene they identified by studying a family with multiple affected children and independently confirmed it in another family.  This finding contributes to solving the genetics of this birth defect and provides affected families with information they can potentially use for pursuing informed reproductive choices. (By Fowzan S Alkuraya, MD FAAP FACMG, http://jmg.bmj.com/content/50/1/54 )