The biological basis of the neurodegenerative movement disorder, Parkinson’s disease (PD), is still unclear despite it being ‘discovered’ over 200 years ago in Western Medicine.

Based on current PD knowledge, there are widely varying theories regarding its pathobiology. This article aimed to explore some of these different theories by summarizing the viewpoints of laboratory and clinician scientists in the PD field on the biological basis of the disease. The personal opinions of the thirteen “PD experts” from six continents are presented in this article to achieve this aim. They offer varied views, ranging from toxin exposure as a PD trigger to LRRK2 as a potential root cause to toxic alpha-synuclein being the most critical etiological contributor. Notably, there is also growing recognition that PD might be better defined with multiple subtypes or as multiple diseases, perhaps each with its own unique pathobiology and treatment regimen. Through the utilization of the content of this article, providers will gain knowledge of the most current theories of PD pathogenesis, enabling them to provide more accurate diagnosis and treatment to people with PD.