The observed increase in ornithine and arginine levels could be indicative of impairment in the urea cycle; ornithine has previously been reported to be increased in PD, purportedly due to a reduction in the ability of mitochondria to transport ornithine for conversion in the urea cycle83 and also as a consequence of ROT exposure, which inhibits the activity of ornithine decarboxylase (Rhee et al., 2016). The gene discussed is ODC1; the disease is Parkinson disease.