Inherited microcephaly exposes Zika culprit Microcephaly has been the terrifying hallmark of the recent outbreak of Zika virus (ZIKV) in the Americas. How the virus damages brain development in the fetus is enigmatic. Chavali et al. found that in congenital microcephaly, mutations in a neural precursor protein, Musashi-1 (MSI1), impede RNA binding to neural stem cell targets, resulting in abnormal brain development (see the Perspective by Griffin). MSI1 also binds ZIKV RNA to amplify viral replication in cells. This interaction could put a pregnant woman at risk of giving birth to a microcephalic child. Furthermore, MSI1 is expressed at high levels in the mouse testis, which may explain the sexual transmission of this virus. Science , this issue p. 83 ; see also p. 33