P4HB and Parkinson disease: Studies have shown that mutations in the PreP (Pre-sequence Protease) and DJ-1/PARK (Parkinson-associated gene DJ-1) genes, as well as mitochondrial stress associated with inhibition of the PDI (protein disulfide isomerase) enzyme, which promotes NO accumulation via the Glutamate receptor (NMDAR) in the brain cell membrane, cause Alzheimer's and Parkinson's in humans (Uehara et al. 2006).