GRIN2B and juvenile Huntington disease: Also, a specific increase in GluN2B-containing NMDARs in medium-sized spiny striatal neurons, specifically at extrasynaptic locations, contributes to phenotype onset in a model of Huntington's disease (Fan et al., 2007; Milnerwood et al., 2010), where the synaptic/extrasynaptic NMDAR balance controls mutant Huntingtin toxicity (Okamoto et al., 2009).