Tsuchida et al. reported that the gene body of FGFR3, the upstream gene of the mitogen-activated protein kinase (MAPK) pathway, which is normally suppressed when α-syn is overexpressed, was hyper-methylated in Lewy body disease (LBD) brains including the DLB PD, and PD with dementia (PDD)27. Here, FGFR3 is linked to Lewy body dementia.