BLOC1S6 encodes a component of the BLOC-1 complex essential for biogenesis of lysosome-related organelles (LROs), particularly platelet dense granules and melanosomes 1. The protein functions in concert with the AP-3 complex to target membrane proteins into vesicles for delivery to axons and nerve terminals, and associates with SNARE proteins to facilitate neurite extension and vesicle docking/fusion [UniProt Function]. BLOC1S6 also participates in melanosome transport and organization, with regulatory variants affecting melanin levels and skin pigmentation diversity in African populations 2. The gene shows upregulation during epithelial-mesenchymal transition induced by extracellular ATP, implicating it in cancer cell invasion pathways 3. Biallelic BLOC1S6 mutations cause Hermansky-Pudlak syndrome type 9 (HPS-9), an autosomal recessive disorder characterized by oculocutaneous albinism, platelet storage pool disease with absent dense granules, and bleeding diathesis 456. BLOC1S6 downregulation also mediates platelet dense granule deficiency in RUNX1 haplodeficiency 1. Disease models indicate BLOC1S6 mutations may increase susceptibility to alveolitis through enhanced inflammatory mediator expression 7.