Conditional knockout of mouse kidney Xpr1 results in reduced proximal tubule Pi efflux, hypophosphatemia, and other abnormalities similar to Fanconi syndrome (Ansermet et al., 2017), which is consistent with XPR1 being the basolateral exit pathway for Pi in the proximal tubule. The gene discussed is XPR1; the disease is Fanconi renotubular syndrome.