OTC and citrullinemia type I: The six UCDs include deficiency of: 1) carbamyl phosphate synthetase; 2) n-acetylglutamate synthetase; 3) ornithine transcarbamylase; 4) argininosuccinic acid synthetase (also called citrullinemia); 5) argininosuccinase acid lyase and; 6) arginase.