Hereditary hypophosphatemic rickets is a group of genetically heterogeneous disorders, consisting of X-linked dominant hypophosphatemic rickets caused by a mutation in PHEX gene, autosomal dominant hypophosphatemic rickets caused by a mutation in FGF23, autosomal recessive hypophosphatemic rickets caused by a mutation in DMP1, ENPP1, FAM20C or SLC34A3 and X-linked recessive hypophosphatemic rickets caused by a mutation in CLCN5. The gene discussed is ENPP1; the disease is X-linked hypophosphatemia.