Microcephaly is a rare disorder that stunts brain development in utero, resulting in babies with abnormally small heads. The Zika virus is one environmental cause of this devastating condition, but genetic defects can cause microcephaly, too. A new study examining three genetic causes of microcephaly in mice suggests one common mechanism through which the disorder could arise. The results could enhance understanding of microcephaly and other neurodevelopmental disorders, including autism.