Urea Cycle disorders (UCDs) are inherited diseases due to a loss of function of one of the enzymes related to urea cycle: deficiency of carbamoyl phosphate synthetase 1 (CPS1D, MIM#237300), ornithine transcarbamylase (OTCD, MIM#311250), argininosuccinatesynthetase (ASSD, MIM#215700), argininosuccinatelyase (ASLD, MIM#207900) and arginase (ARG1D, MIM#207800), the mitochondrial ornithine-citrulline antiporter (ORC1D, MIM#238970) and the CPS1-activating enzyme N-acetylglutamate synthase (NAGSD, MIM#237310) [1]. The gene discussed is OTC; the disease is urea cycle disorder.