CD200R1 and Parkinson disease: Although it is difficult to compare the observations in iPSC-derived neurons and in brain tissue, these results may indicate that changes in the CD200-CD200R1 ligand-receptor pair occurred specifically in DAn at modelled early stages of the disease although they were not observed at end stages of PD in post-mortem substantia nigra tissue samples, where 40–90% of DAn are dead.