FMR1 and fragile X syndrome: Research implied a contribution from defective programed cell death to the excessive synaptic connections in Fmr1 mutants and behavioral phenotype of children with FXS (Gatto and Broadie, 2011; Cheng et al., 2013), which was also in accordance with our finding that Tnfsf10 mRNA level was significantly decreased in Fmr1 KO mice.