We found that Parkinson’s disease was significantly associated with cholinergic and monoaminergic neurons (Figure 2A and Table S3). This cluster consists of neurons (Table S4) that are known to degenerate in Parkinson’s disease 32–34, such as dopaminergic neurons from the substantia nigra (the hallmark of Parkinson’s disease), but also serotonergic and glutamatergic neurons from the raphe nucleus 35, noradrenergic neurons 36, as well as neurons from afferent nuclei in the pons 37 and the medulla (the brain region associated with the earliest lesions in Parkinson’s disease 32). In addition, hindbrain neurons and peptidergic neurons were also significantly associated with Parkinson’s disease (with LDSC only). Therefore, our results capture expected features of Parkinson’s disease and suggest that biological mechanisms intrinsic to these neuronal cell types lead to their selective loss. Interestingly, we also found that enteric neurons were significantly associated with 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,
