FXR2 and fragile X syndrome: Circadian rhythm-dependent alteration of gene expression has been observed in dfmr1 mutant fly heads (Xu et al., 2012) and liver tissue from Fmr1 KO, Fxr2 KO and Fmr1/Fxr2 double KO mice (Zhang et al., 2008) and a decrease in expression of circadian-related genes has been observed in lymphoblastoid cell lines from FXS patients (Mullegama et al., 2015).