GRIN2B and Huntington disease: In HD, increased calpain activity leads to activation of calcineurin, which dephosphorylates the striatal enriched tyrosine phosphatase (STEP), an enzyme able to dephosphorylate the tyrosine 1472 residue of the GluN2B subunit, leading to reduced synaptic NMDAR expression and lateral diffusion of the GluN2B-containing receptors to extrasynaptic sites [23,127,131,132,133].