FGF23 and hypophosphatemia: The positive family history may corroborate a genetic cause for hypophosphatemia, which is further proven by genetic testing, including PHEX mutation for XLH, mutations in the FGF23 gene causing ADHR (including R176Q, R176W, R179Q, R179W), and mutations for autosomal recessive hypophosphatemic rickets (ARHR), including inactivating mutations in the DMP1 gene, ENPP1 gene, and mutations in the FAM20C gene encoding a protein kinase [19–21].