Standardized protocol to detect phosphorylated α-synuclein in skin biopsies: recommendations from an expert panel

BACKGROUND: Skin biopsy is a promising diagnostic tool for the in vivo identification of Parkinson's disease and other α-synucleinopathies. However, despite increasing adoption, methodological variability exists among different laboratories applying this technique. To move toward a formal standardized protocol, leading experts in the field convened for a meeting focused on discussing and harmonizing the main methodological differences. The outcome of this meeting was a consensus-based skin biopsy protocol, which is here presented. RESULTS: A formal expert opinion conference was held on November 15-16, 2024, at the IRCCS Institute of Neurological Sciences of Bologna (Italy). The consensus was reached by using a Question & Answer format following the PICO (Population, Intervention, Comparison, Outcome) methodology. An online Delphi survey was then performed based on the contrasting issues raised during the meeting. Unanimous consensus was reached on key elements, including the skin biopsy technique, choice of fixative, use of a cryostat, staining method for phosphorylated α-synuclein (p-α-syn), use of high-power fluorescence microscope, co-localization of p-α-syn with neuronal or glial markers, and high-magnification analysis. Additional agreement, achieved through the Delphi method, concerned specific procedural parameters such as the number of samples and section thickness, punch diameter, preferred biopsy sites in cases of asymmetric motor involvement, quantitative methods for assessing p-α-syn load, and use of p-α-syn as the optimal marker for identifying misfolded α-synuclein in the skin. Conclusions We have developed a consensus-based protocol for the detection of p-α-syn in skin samples from patients with suspected α-synucleinopathies, with the aim of promoting standardization, a broader adoption of the method, and its translation into clinical practice.