Mice with fragile X syndrome are a common model for autism because the mice exhibit exaggerated repetitive behavior typical of the disorder. Researchers have for the first time gotten CRISPR into the brain to successfully edit a gene and reduce repetitive behavior. The CRISPR-Gold technique knocked out a gene for a neurotransmitter receptor, damping overexcitation and associated burying behavior. The technique could allow CRISPR therapies for other brain disorders.