Approximately 50% of infants with GACI type 1 (bi-allelic ENPP1 deficiency) will succumb to disease by 6 months of age (5), and almost invariably those who survive will develop a severe phosphate wasting rickets known as autosomal recessive hypophosphatemic rickets type 2 (ARHR2) (6, 7). The gene discussed is ENPP1; the disease is hypophosphatemic rickets, autosomal recessive, 2.