Does Parkinson’s Start in the Brain or the Gut?

Where does Parkinson’s disease (PD) begin? In the brain or in the gut? According to new findings, both are possibilities.
In a new Danish study, scientists hypothesize that PD can be divided into two subtypes: gut-first, meaning it originates in the peripheral nervous system (PNS) of the gut and spreads to the brain; and brain-first, originating in the brain, or entering the brain via the olfactory system, and spreading to the brainstem and peripheral nervous system.
“The discussion