Reproductive Biology Cardiac and craniofacial birth defects are common, but many cannot be attributed to specific mutations. An environmental trigger associated with these birth defects is maternal fever during the first trimester. Using chick and zebrafish embryos, Hutson et al. found that hyperthermia activated temperature-sensitive TRPV1 and TRPV4 ion channels in neural crest cells, which give rise to the tissues affected by the birth defects. Transiently activating either of these channels in neural crest cells in chick embryos resulted in cardiac and craniofacial birth defects similar to those induced by fever. Sci. Signal. 10 , eaal4055 (2017).