We utilized 5 murine models of HPS, including the double-mutant HPS1/2 murine model, which exhibits spontaneous progressive fibrosis with aging, as well as the single-mutant HPS1 and HPS2 models, which best reflect human disease genetics while exhibiting fibrotic sensitivity without spontaneous fibrosis (Table 1) (8, 10–12). The gene discussed is AP3B1; the disease is Hermansky-Pudlak syndrome.