Parkinson's disease (PD) is a neurodegenerative disorder, affecting 1.8% of individuals over the age of 80 years globally, with an increasing prevalence due to the progressive aging of the population . PD is characterized by the abnormal accumulation of misfolded alpha-synuclein (α-syn) inside neurons, leading to the formation of Lewy Bodies, which promote neuroinflammation and the irreversible degeneration of dopaminergic neurons in the substantia nigra pars compacta and other brain regions , , , . The clinical hallmarks of PD are tremor, bradykinesia, rigidity, and later in the disease, postural instability . However, these typical motor features do not become evident until 60-80% of dopaminergic neurons are lost, such that other indicators are needed for earlier diagnosis . Nonmotor symptoms related to PD, such as constipation and REM-sleep behavior disorder (RBD), can occur decades before the onset of the classical motor symptoms but often go unrecognized , , , . Since not all PD patients have Lewy bodies or positive α-syn readings , , recently, a biological classification of PD has been proposed for research purposes, which considers the presence or absence of α-syn pathology, features of neurodegeneration, and genetic contributions .