CDO1 and Parkinson disease: Cysteine regulates CDO1 turnover through Ubiqutin-26S proteasome-mediated degradation [15], and a high level of cysteine is cytotoxic and can cause rheumatoid arthritis [16], [17], [18], Parkinson’s disease [17], Alzheimer’s disease [17], increased risk of cardiovascular disease [19] and adverse pregnancy outcomes [20].