RAB39B and Parkinson disease: Some of the genes mutated in PD encode for proteins involved in synaptic functions, such as: Ras-associated binding protein 39b (Rab39b), synaptojanin 1 (SYNJ1), Leucine-rich repeat kinase 2 (LRRK2), synphilin-1 (SYPH1) and transmembrane protein 230 (TMEM230) [21,22,23,24,25,26,27,28,29,30,31,32,33].