For example, urea cycle dysregulation (UCD) is a common metabolic hallmark in various types of cancer, which is featured by downregulation of UC enzymes and several key enzymes in citrulline-arginine cycle, such as argininosuccinate synthase (ASS1), carbamoyl phosphate synthase 1 (CPS1), and ornithine carbamoyltransferase (OTC) 19, 20. Here, OTC is linked to urea cycle disorder.