Figure 3.

Relevant changes over time in PD. PD is characterized by a profound loss of DA neurons within the SNpc, which is diagnosed using confirmatory SPECT imaging. Although there are currently no approved biomarkers to identify PD patients in earlier stages of disease, declines in PD patient microbiome diversity and elevations in pathological forms of α-synuclein prior to symptom onset have been well documented. Sampling PD patient stool, CSF, and blood holds promise for identifying prodromal (shown in left column) patients and monitoring disease progression during the symptomatic (shown in right column) stage of pathology. Within each specified sampling compartment, arrows pointing up represent elevations in biomarkers that occur during pathology, while arrows pointing down represent declines in these biomarkers.