ARG1 and urea cycle disorder: Argininemia, caused by a deficiency of arginase 1 whose role is to decompose of arginine into ornithine and urea, is a rare autosomal recessive urea cycle disorder and according to the data from newborn screening records and the urea cycle disorders (UCDs) consortium's study, the incidence of arginase 1 deficiency has been estimated at about 1:950,000,[1] accounting for 3.5% of all UCDs.[2] Unlike other urea cycle disorders, patients with arginineemia rarely develop hyperammonemia.