FMR1 and fragile X-associated tremor/ataxia syndrome: As PTMs of FMRP are dependent on mGluR5 activation (Westmark and Malter, 2007), the reduction in mGluR5 receptors in FXTAS neurons may be responsible for altered FMRP-PTMs and consequentially reduced FMRP-mediated clearance of clearance of RNA granules, spine density and maturation, as well as increased excitotoxicity of the remaining mGluR5s.