Depletion of Xpr1 in mice is lethal, emphasizing the key role of this gene in phosphate homeostasis23 and we have previously shown that mutations in the cytoplasmic N-terminal domain of XPR1 associated to PFBC lead to a defective phosphate export in vitro and ex vivo6,11. The gene discussed is XPR1; the disease is bilateral striopallidodentate calcinosis.