Although the molecular function of BLOC-2 in LRO biogenesis is incompletely known, disorders such as pigmentation and bleeding are mildly affected in BLOC-2 (HPS3, HPS5, and HPS6) mouse models (Suzuki et al., 2001; Zhang et al., 2003), and most of the cases reported so far have comparably shown that HPS patients with BLOC-2 mutations tend to have a mild form of the disease, with no lung or immune involvement. This evidence concerns the gene HPS5 and Hermansky-Pudlak syndrome.