SNCA and Parkinson disease: PD is a neurodegenerative disease characterized by a loss of dopaminergic neurons in the substantia nigra pars compacta and the deposition of insoluble alpha-synuclein polymers in neurons, forming Lewy bodies.130 Approximately 80% of PD patients suffer from GI dysfunction.131 PD patients commonly suffer from symptoms such as constipation, which precede the clinical diagnosis of PD and its other hallmark symptoms such as bradykinesia and dementia,131 indicating that gut dysfunction may play a role in the pathogenesis of PD.