Among the xanthine derivatives, 8-styrylxanthine group includes compounds such as istradefylline (5, Figure 2), an A2A receptor antagonist used as an adjunct therapy for PD, and 8-chloro-styrylcaffeine (233, Figure 41), which also act as an A2A antagonist and MAO-B inhibitor. The gene discussed is MAOB; the disease is Parkinson disease.