Comments on the article by C. H. McNaughton et al.. Individuals with fragile X syndrome (FXS) show varying degrees of social behavior disturbances, from social anxiety to autism. This variability of social behavior phenotypes in FXS is likely to be due to interactions of Fmr1 with other gene variants and environmental factors during brain development, although very little is known about the specific genetic and neural mechanisms involved. The Fmr1 knockout mouse is an important experimental resource for elucidating the neural mechanisms of social anxiety, social reward, and social cognition. However, studies of social behavior phenotypes in the Fmr1 knockout mouse are still in early stages. McNaughton et al provide important new information on these phenotypes in the Fmr1 knockout mouse through their use of novel, detailed behavioral analysis to identify signs of increased social anxiety and social cognition deficits. Their significant refinements in measurement of social behavior phenotypes will help to advance future efforts to elucidate the genetic and neural mechanisms underlying social behavior disturbances in FXS and autism.