Likewise in young FXS mice (2–3 weeks) mGluR5 mediated LTD is unaffected (Desai et al., 2006; Meredith et al., 2007), although in adult mice a deficit in coupling between mGluR5 activation and retrograde signaling appears to be responsible for a loss in eCB-LTD (Jung et al., 2012). The gene discussed is GRM5; the disease is fragile X syndrome.