Immunoprecipitation with an antibody against the RSK consensus site and western blotting with an antibody that recognizes all phosphorylation sites of Shank resulted in a higher phosphorylation of Shank in cortical synaptosomes of Fmr1 knock-out mice, indicating that RSK activity is associated with Shank phosphorylation in the FXS. The gene discussed is RPS6KA3; the disease is fragile X syndrome.