Identification of the genes responsible for recognized neurogenetic syndromes with high prevalence of ASD, such as FMR1 and TSC1/2, and localization of causative genes within microdeletions associated with non-syndromic (idiopathic) autism, such as SHANK3, NLGN3, and NLGN4, have highlighted the role of single-gene mutations in disease pathogenesis (reviewed in [1]–[4]). The gene discussed is NLGN4X; the disease is autism.