Enteric nervous system α-synuclein immunoreactivity in idiopathic REM sleep behavior disorder

Objective:To investigate the expression of -synuclein in colonic biopsies of patients with idiopathic REM sleep behavior disorder (iRBD) and address if -synuclein immunostaining of tissue obtained via colonic biopsies holds promise as a diagnostic biomarker for prodromal Parkinson disease (PD).Methods:Patients with iRBD, patients with PD, and healthy controls were prospectively recruited to undergo colonic biopsies for comparison of -synuclein immunoreactivity patterns between the groups by using 2 different antibodies.Results:There was no difference in colonic mucosal and submucosal immunostaining between groups using the 15G7 -synuclein antibody, which was found in almost all participants enrolled in this study. By contrast, immunostaining for serine 129-phosphorylated -synuclein (pSyn) in submucosal nerve fibers or ganglia was found in none of 14 controls but was observed in 4 of 17 participants with iRBD and 1 out of 19 patients with PD.Conclusions:The present findings of pSyn immunostaining of colonic biopsies in a substantial proportion of iRBD participants raise the possibility that this tissue marker may be a suitable candidate to study further as a prodromal PD marker in at-risk cohorts.