BLOC1S3 is a subunit of the biogenesis of lysosomal organelles complex 1 (BLOC-1), which mediates biogenesis of lysosome-related organelles including melanosomes and platelet dense granules 1. As a BLOC-1 component, BLOC1S3 functions in intracellular vesicle trafficking and, in concert with the AP-3 complex, directs membrane protein cargos into vesicles for delivery to neurites and nerve terminals 2. BLOC1S3 mutations cause Hermansky-Pudlak syndrome type 8 (HPS-8), characterized by oculocutaneous albinism and platelet dysfunction 1. HPS-8 is clinically milder than other HPS forms, typically presenting with moderate albinism and bleeding diathesis without systemic complications like pulmonary fibrosis 3. Loss of BLOC1S3 function causes aberrant melanosomal protein localization, with increased trafficking of cargo proteins like TYRP1 to the plasma membrane 2. Additionally, BLOC1S3 variants show genome-wide association with late-onset Alzheimer disease (rs597668, P=6.45×10⁻⁹), though clinical utility for disease prediction remains limited 4. These findings establish BLOC1S3 as essential for proper organellar biogenesis and melanosome organization.