The association of oligodendrocytes with Parkinson’s disease was more unexpected. A possible explanation is that this association could be due to a related disorder (e.g., multiple system atrophy, characterized by Parkinsonism and accumulation of α-synuclein in glial cytoplasmic inclusions 69). However, this explanation is unlikely as multiple system atrophy is a very rare disorder; hence, only a few patients are likely to have been included in the Parkinson’s disease GWAS which could not have affected the GWAS results. In addition, misdiagnosis is unlikely to have led to the association of Parkinson’s disease with oligodendrocytes. Indeed, we found a high genetic correlation between self-reported diagnosis from the 23andMe cohort and a previous GWAS of clinically-ascertained Parkinson’s disease 19. In addition, self-report of Parkinson’s disease in 23andMe subjects was confirmed by a neurologist in all 50 cases evaluated 70.
