Parkinson’s disease (Figure 2A), which is consistent with Braak’s hypothesis, which postulates that Parkinson’s disease could start in the gut and travel to the brain via the vagus nerve 38,39. Furthermore, we found that oligodendrocytes (mainly sampled in the midbrain, medulla, pons, spinal cord and thalamus, Figure S8) were significantly associated with Parkinson’s disease, indicating a strong glial component to the disorder. This finding was unexpected but consistent with the strong association of the spinal cord at the tissue level (Figure 1C), as the spinal cord contains the highest proportion of oligodendrocytes (71%) in the nervous system 30. Altogether, these findings provide genetic evidence for a role of enteric neurons, cholinergic and monoaminergic neurons, as well as oligodendrocytes in Parkinson’s disease etiology.
