93. Phosphorylated α-synuclein biomarker in skin nerves is differently expressed in pure autonomic failure and idiopathic Parkinson disease

The aim of this study was to characterize the expression in skin nerves of native (n-syn) and misfolded or phosphorylated (p-syn) α-synucleins in pure autonomic failure (PAF) and idiopathic Parkinson disease (IPD). We studied 30 patients, including 16 well-characterized IPD, 14 patients fulfilling PAF diagnostic criteria, and 15 age-matched controls. Subjects underwent skin biopsy from cervical, thigh and leg sites to study small nerve fibers and intraneural n-syn and p-syn. PAF and IPD both showed a skin denervation, more severely expressed in patients with higher p-syn load. N-syn was similarly expressed in both groups of patients and controls. By contrast, p-syn was not found in controls, but it was disclosed in all PAF and IPD patients with different skin innervation. In addition, abnormal α-syn deposits were found in all analysed skin samples in PAF, but in 49% of samples only with higher positivity rate in the cervical site in IPD. In conclusion: (1) intraneural p-syn was a reliable in vivo marker of PAF and IPD; (2) neuritic p-syn inclusions differed in PAF and IPD, suggesting a different underlying pathogenesis; (3) searching for abnormal p-syn deposits in skin nerves, the site of analysis is irrelevant in PAF, but it is critical in IPD.