FGF23 and autosomal dominant hypophosphatemic rickets: Hypophosphatemia owing to renal phosphate wasting is inherited most frequently as an X-linked dominant disorder (XLH), which is caused by dominant mutations in the PHEX gene, or as an autosomal dominant condition (ADHR), which is caused by heterozygous mutations in the fibroblast growth factor 23 gene (FGF23).(1) Recently, homozygous mutations in the gene encoding DMP1 (dentin matrix protein 1), a noncollagenous phosphoprotein, were identified as the cause of an autosomal recessive form of hypophosphatemia (ARHP).(2,3)