The main limitation is the inclusion of PD patients without screening for common PD-causative genes and sporadic PD causative factors (e.g., SNCA, GBA, MAPT and LRRK2 genes), which might mask the effect of ADORA2A rs5760423 and CYP1A2 rs762551. The gene discussed is CYP1A2; the disease is Parkinson disease.