S100B and Parkinson disease: OPALIN (also denominated as Tmem) is a marker of myelinating oligodendrocytes,63 while S100B has been associated with glial stress response in Parkinson’s disease post-mortem midbrain.64 When comparing idiopathic Parkinson’s disease oligodendrocyte density across this trajectory, we found a reduced fraction of myelinating OPALINhigh cells compared to controls (Fig. 4J and Supplementary Fig. 6).