Biomarkers of Parkinson's Disease: An Introduction.

The development of biomarkers is of great importance in Parkinson's disease (PD) as it may contribute to confirmation and support of the diagnosis, tracking of progression, and prediction of the natural history of PD. Biomarkers also help in the identification of targets for treatment and measuring the efficacy of interventions. Biomarkers are, therefore, crucial to understanding the pathophysiology of PD, the second commonest neurodegenerative disorder in the world. Modern understanding of PD suggests that it is a multipeptide, multiorgan disorder presenting with a heterogeneous clinical condition, both motor and nonmotor. Biomarkers need to reflect this neuropathological and clinical heterogeneity of PD. In this review, we outline some key advances in the field of clinical, genetic, neuroimaging, and tissue-based biomarkers proposed or used for PD. The individual sections will be covered in relevant chapters and our review is largely a primer aimed to alert readers to the current state of the various biomarkers proposed for PD. In doing so, we have also underlined the important role multimodal rather than single biomarkers could play in our future understanding of PD.