Current Parkinson's disease (PD) therapy is essentially symptomatic, and L-Dopa (LD), is the treatment of choice in more advanced stages of the disease. However, motor complications often develop after long-term treatment, and at this point physicians usually prescribe adjuvant therapy with other classes of antiparkinsonian drugs, including dopamine (DA) agonists, anticholinergic, catechol-O-methyl transferase (COMT) or monoamine oxidase (MAO)-B inhibitors. The gene discussed is COMT; the disease is Parkinson disease.