In autosomal recessive hypophosphatemic rickets type 2 (ARHR2), ectonucleotide pyrophosphatase/phosphodiesterase family member 1 (ENPP1) fails to keep FGF23 levels low due to inactivating mutations in the ENPP1 gene resulting in hypophosphatemia [54]. The gene discussed is FGF23; the disease is hypophosphatemic rickets, autosomal recessive, 2.