Biomarkers in Parkinson’s Disease

Parkinson’s disease (PD) is the second most common neurodegenerative disorder, with a documented significant increase in its prevalence in the past three decades. Both environmental and genetic factors contribute to the pathophysiology of this disorder. The diagnosis relies mainly on clinical findings, and currently, there is no reliable and trustworthy method of early identification of PD except for genetic testing limited to rare cases of monogenic forms of the disease. Current scientific research is focused on the identification of new diagnostic criteria and new disease biomarkers, allowing correct and timely diagnosis. Various types of potential PD biomarkers have been tested, including clinical, imaging, pathological, biochemical, and genetic, but none of them can be considered excellent or even satisfactory. However, several recent developments raise hope that early diagnosis of PD will be possible in the near future. The finding of reliable PD biomarkers may happen due to the successes in the field of neuroimaging, including positron emission tomography (PET), single-photon emission CT (SPECT), novel MRI techniques, as well as a result of the progress of new biochemical methods. Examples of these methods include aggregated α-synuclein measurements by real-time quaking-induced conversion (RT-QuIC), protein misfolding cyclic amplification (PMCA), and development of epigenetic-based biomarkers. Besides, a combination of biomarkers looks very promising to maximize their utility and ensure an accurate diagnosis of premotor or early-stage PD. Our goal here is to provide the reader with new developments in biomarkers suitable for early PD identification and to highlight the advantages and limitations of an existing individual biomarker and their combination.