XPR1 and bilateral striopallidodentate calcinosis: Dominantly inherited PFBC is linked to pathogenic variants in four genes: solute carrier 20 member 2 (SLC20A2), xenotropic and polytropic retrovirus receptor 1 (XPR1), platelet‐derived growth factor B (PDGFB), and platelet‐derived growth factor receptor B (PDGFRB).