FMR1 and fragile X syndrome: Moreover, several studies showed that lithium, an FDA-approved drug that inhibits GSK3β activity, alone or in conjunction with mGluR5 antagonists, mitigated many of the symptoms of FXS in Fmr1 KO mice, from the cellular level to behavior associated with FXS and ASDs (Min et al., 2009; Yuskaitis et al., 2010; Mines and Jope, 2011).