Since alveolar type II cells highly express Rab38, similar to melanocytes and platelets [14,21,24,25], it seems rational to hypothesize that Rab38 deficiency may cause the HPS lung phenotype that is closely associated with abnormalities in alveolar type II cell morphology and lung surfactant metabolism. This evidence concerns the gene RAB38 and Hermansky-Pudlak syndrome.