Because of the importance of Rab38 and its activator BLOC-3 in melanogenic enzyme trafficking (Loftus et al., 2002; Gerondopoulos et al., 2012), defects in Rab38 cause the diluted coat color of chocolate mice, and defects in BLOC-3 cause the hypopigmentation seen in type 1 and type 4 HPS patients. Here, RAB38 is linked to Hermansky-Pudlak syndrome.