ECM1 and Parkinson disease: The remaining three identified tryptic peptides were derived from proteins involved in the regulation of cellular communication (Multiple epidermal growth factor-like domains protein 8), extracellular structural function (Extracellular matrix protein 1), and protein glycosylation (Protein O-linked-mannose beta-1,2-N-acetylglucosaminyltransferase 1), with no known relation with neurodegeneration or previous link with parkinsonism.