A mutation may explain the sudden rise in birth defects from Zika

A single genetic mutation made the Zika virus far more dangerous by enhancing its ability to kill nerve cells in developing brains, a new study suggests. The small change — which tweaks just one amino acid in a protein that helps Zika exit cells — may cause microcephaly, researchers report September 28 in Science. The mutation arose around May 2013, shortly before a Zika outbreak in French Polynesia, the researchers calculate. Zika virus was discovered decades ago but wasn’t associated with microcephaly — a birth defect characterized by a small head and brain — until the 2015–2016 outbreak in Brazil. Women who had contracted the virus while pregnant started giving birth to babies with the condition at higher-than-usual rates. Researchers weren’t sure why microcephaly suddenly became a complication of Zika infections, says Pei-Yong Shi, a virologist at the University of Texas Medical Branch at Galveston. Maybe the virus did cause microcephaly before, scientists...