Neuropathological investigations in the autopsied brain of patients with PD have indicated that the disease manifests as dopaminergic neuronal degeneration in the ventrolateral substantia nigra in the early stage, which progresses to the midbrain and other regions of the brain in the later stages, along with increased levels of MAO-A and MAO-B [2,54]. This evidence concerns the gene MAOA and Parkinson disease.