Specifically, polymorphisms in genes involved in dopamine synthesis and metabolisms, such as catechol-O-methyltransferase (COMT), monoamine oxidase-B (MAO-B), dopa decarboxylase, Dopamine receptors, and Dopamine transporter genes, influence the amount of Levodopa intake, clinical response to the drug, risk of developing motor fluctuations, dyskinesias, and drug-induced adverse reactions (hallucinations, psychotic episodes, impulse control disorders, gastrointestinal adverse effects, sleep attacks) [266,267]. The gene discussed is MAOB; the disease is drug-induced dyskinesia.