RAB39B and Parkinson disease: Since loss-of-function RAB39B mutations are associated with PD that has dramatic dopaminergic neuronal loss and dopamine dyshomeostasis during neurodegeneration (Masato et al., 2019; Shao and Le, 2019), we studied levels of dopamine and the dopaminergic neuronal marker tyrosine hydroxylase (TH) in the midbrain of 2 months old Rab39b KO mice.