The localization of FMRP to dendritic spines and the putative function of many of its target mRNAs at or near synaptic contacts add further support to the possibility that FXS is a disorder of synaptic development and function (Irwin et al., 2000; Huber et al., 2002; Bear et al., 2004). Here, FMR1 is linked to fragile X syndrome.