May function in the pathway of organelle biogenesis. Defects in HPS4 are the cause of Hermansky-Pudlak syndrome type 4 (HPS4). Hermansky-Pudlak syndrome (HPS) is a genetically heterogeneous, rare, autosomal recessive disorder characterized by oculocutaneous albinism, bleeding due to platelet storage pool deficiency, and lysosomal storage defects. This syndrome results from defects of diverse cytoplasmic organelles including melanosomes, platelet dense granules and lysosomes. Ceroid storage in the lungs is associated with pulmonary fibrosis, a common cause of premature death in individuals with HPS. 4 isoforms of the human protein are produced by alternative splicing. Note: This description may include information from UniProtKB.