In the context of MPTP-induced Parkinsonism, mitochondria are especially important “players” as the outer mitochondrial membrane enzyme, MAO B, catalyzes the conversion of MPTP in the active toxin, MPP+, which inhibits complex I of the respiratory chain, thus creating the conditions for the development of mitochondrial dysfunction [2,3,4,5]. The gene discussed is MAOB; the disease is Parkinson disease.