FAM20C and X-linked hypophosphatemia: The most common form of FGF23-mediated hypophosphatemic rickets is X-linked hypophosphatemia (XLH), caused by loss-of-function pathogenic variants in PHEX.6 Additional inheritable forms include autosomal dominant hypophosphatemic rickets caused by a variant in FGF23 and three forms of autosomal recessive hypophosphatemic rickets caused by variants in dentin matrix protein 1 (DMP-1) (autosomal recessive hypophosphatemic rickets type 1, ARHR1), ENPP1 (ARHR2) or family with sequence similarity 20, member C (FAM20C) (autosomal recessive hypophosphatemic rickets type 3, ARHR3).6