Review
Qihan Song, Wenjiao Yu, Shun Yu,
Parkinson’s disease (PD) is a common neurodegenerative disease, characterized clinically by both motor and non-motor symptoms. Pathologically, PD is hallmarked by the loss of dopaminergic neurons in the substantia nigra (SN) and the formation of α-synuclein (α-syn) containing inclusion bodies (Lewy pathology) in the surviving neurons. Diagnosis of PD is still based on clinical features. However, owing to the complexity, heterogeneity, and overlapping of its symptoms with other Parkinsonian disorders, correct diagnosis of PD remains a challenge, especially in the early stages. Therefore, there is an urgent need for biomarkers that can help correctly diagnose PD, differentiate PD from other Parkinsonian disorders, monitor the progression of the disease, and evaluate the therapeutic efficacy. Various molecules have been investigated for their utility in diagnosing PD, among which α-syn is the most extensively investigated one due to its close implication in the etiology and pathogenesis of PD and related diseases. During the past decade, various species of α-syn, including total, oligomeric, and phosphorylated α-syn in various tissues, have been investigated for their utility as a potential biomarker for PD diagnosis and differential diagnosis. Various forms of α-syn in body fluids, including cerebrospinal fluid (CSF), blood plasma, and saliva, are among the ones that are extensively investigated, since the body fluids are relatively accessible compared to the peripheral tissues. The aim of this review is to summarize the progress of studies on the utility of α-syn in body fluid as a biomarker for PD diagnosis and differential diagnosis.