CA2 and Parkinson disease: Moreover, loss of function of Rab39B, a small GTPase that is involved in endosome trafficking and that is associated with early-onset PD, has recently been shown to alter the trafficking of an α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR) subunit and to steer AMPAR toward forming a Ca2+-permeable channel (Table 1) (Lesage et al., 2015; Mignogna et al., 2015).