About 30% of patients with Parkinson's disease (PD) develop Parkinson's disease dementia (PDD) in the course of the disease. Until now, diagnosis is based on clinical and neuropsychological examinations, since so far there is no laboratory marker. In this study we aimed to find a neurochemical marker which would allow a risk assessment for the development of a dementia in PD patients. For this purpose, we adopted a gel-free proteomic approach (iTRAQ-method) to identify biomarker-candidates in the cerebrospinal fluid (CSF) of patients with PD, PDD and non-demented controls (NDC). Validation of these candidates was then carried out by multiple-reaction-monitoring (MRM) optimised for CSF. Using the iTRAQ-approach, we were able to identify 16 differentially regulated proteins. Fourteen out of these 16 proteins could then be followed-up simultaneously in our optimised MRM-measurement protocol. However only Tyrosine-kinase-non-receptor-type 13 and Netrin-G1 differed significantly between PDD and NDC cohorts. In addition, a significant difference was found for Golgin-160 and Apolipoprotein B-100 between PD and NDC. Apart from possible pathophysiological considerations, we propose that Tyrosine-kinase non-receptor-type 13 and Netrin G1 are biomarker candidates for the development of a Parkinson's disease dementia. Furthermore we suggest that iTRAQ and MRM are valuable tools for the discovery of biomarker in cerebrospinal fluid. However further validation studies need to be done with larger patient cohorts and other proteins need to be checked as well.
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