Because L-dopa is proven to be the most effective drug for treating PD, the use of enzyme inhibitors (dopa decarboxylase inhibitors, COMT inhibitors and MAO-B inhibitors) to extend the duration of action of each dose of L-dopa or the dopamine derived from L-dopa, has proven another effective means of treating ‘wearing off’. The gene discussed is MAOB; the disease is Parkinson disease.