Another potentially significant point of comparison is with familial idiopathic basal ganglia calcification (Fahr’s disease) which is a common cause of intracranial calcification in humans (49) An emerging picture of the pathology in familial idiopathic basal ganglia calcification is that it arises from deficiencies in ion homeostasis across the blood–brain barrier, either via mutations in ion transporters themselves (SLC20A2 (50) or XPR1 (51)), or in genes that play a role in pericyte growth factor responses (PDGFB (52) or PDGFRB (53)) and thereby blood–brain barrier permeability. Here, XPR1 is linked to calcification.