ASL and Parkinson disease: Furthermore, genes involved in the synthesis of arginine (ornithine carbomoyltransferase, Q = 0.021; argininosuccinate synthase, Q < 0.0001; and argininosuccinate lyase, Q < 0.0001) were present at a lower frequency in PD patients than in HCs, and genes involved in the consumption of arginine (arginase, Q < 0.0001) were present at a higher frequency in PD patients than in HCs.