A team of scientists at CalTech, led by Sarkis Mazmanian, PhD, have discovered a "functional link between bacteria in the intestines and Parkinson's disease." (Dajose) The research team decided to focus on gut bacteria because 75% of Parkinson's disease (PD) sufferers have some form of gastrointestinal abnormality, and almost all PD patients have a buildup of a protein called alpha-synuclein (αSyn) in both the brain and the gut.
Professor Mazmanian noticed that gastrointestinal issues preceded the motor symptoms experienced by Parkinson's patients by many years. That information, coupled with the fact that 70% of the peripheral nervous system is in the intestines and is directly connected to the central nervous system via the vagus nerve, influenced the course of this research. In studies conducted on genetically-related mice with high levels of αSyn – one cohort with a microbiome, and a second cohort that was bred in a sterile environment (labeled the germ-free cohort) – the germ-free mice displayed almost zero motor symptoms compared with their counterparts. After exposing the mice to short-chain fatty acids (SCFAs), which have been shown to trigger immune responses in the brain, the germ-free cohort began to exhibit motor symptoms indicative of PD.