ITPR1 and Huntington disease: Cytoplasmic calcium concentration has been shown to be increased in SPNs from HD model mice as a result of increased entry through N-methyl-D-aspartate receptors (NMDARs), whose subunit composition and localisation in these cells is altered (Milnerwood et al., 2010, 2012), and sensitisation of the inositol 1,4,5-trisphosphate receptor (IP3R), which results in increased release of Ca2+ from the endoplasmic reticulum (ER) (Tang et al., 2003; Ryskamp et al., 2017).