Dopamine replacement therapy and subthalamic deep-brain stimulation (DBS) are established treatments for PD; unfortunately, some motor and non-motor symptoms in PD do not seem to respond well to levodopa, DBS, or other forms of dopaminergic medications (such as monoamine oxidase-B [MAO-B] inhibitors and dopamine agonists) or appear to be resistant to such dopaminergic treatments with increased PD duration and disease progression. The gene discussed is MAOB; the disease is Parkinson disease.