ENPP1 and autosomal recessive hypophosphatemic rickets: Autosomal-recessive forms of hypophosphatemic rickets (ARHR) may be caused by mutations in dentin matrix protein 1 (DMP1, as in ARHR1) or ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1, as in ARHR2).