Biomarkers of Parkinson’s disease

Biomarkers for Parkinson’s disease (PD) are absolutely needed both to achieve an early/differential diagnosis and to find disease-modifying treatments. This chapter will focus on the different biomarkers suggested up to now, divided in three main categories: clinical, functional and molecular. In particular, cost and specificity of each proposed biomarker are taken into account, as well as the possibility of exploitation in the routine clinical practice. Quite often each single biomarker suffers of main issues: the lack of specificity for PD and consequently the need of a critical evaluation by the clinician; the high cost per single observation, that reduces the analyses performed and the centers properly equipped; the discomfort for the patient or his exposure to ionizing radiation, that limits the investigation to borderline cases; the need for highly specialized technicians to perform the analysis, that makes difficult to extend it to general public health centers. Moreover, molecular biomarkers are the results of discovery studies requiring extensive validation before acceptance. This step needs standard procedures, a large and heterogeneous cohort of subjects, an established network of collaborating centers. The high costs and the technical hints of this step are the bottleneck that currently hampers the availability of biological biomarkers.