L1CAM and Parkinson disease: In 226 subjects (18 RBD, 77 PD, 36 PDD, 11 DLB, 69 HC, 15 FTD), we also asked whether elevated α-synuclein in Lewy body disease is phosphorylated at serine 129 (pSer129) in L1CAM-positive exosomes and has a value as a blood-based biomarker.