BLOC1S5 encodes the Muted subunit of the BLOC-1 (biogenesis of lysosomal organelles complex 1), a critical component required for biogenesis and trafficking of lysosome-related organelles (LROs) including melanosomes and platelet dense granules 1. As part of the BLOC-1 complex, BLOC1S5 functions in concert with the AP-3 complex to target membrane proteins into vesicles for delivery to neuronal terminals and to facilitate neurite extension through interactions with SNARE proteins 1. The protein plays essential roles in melanosomal biogenesis and anterograde axonal transport. Pathogenic variants in BLOC1S5 cause Hermansky-Pudlak syndrome type 11 (HPS-11), characterized by oculocutaneous albinism, bleeding diathesis, platelet aggregation defects, and dramatically reduced platelet dense granules 123. Disease-causing mutations impair BLOC-1 complex assembly and function 1. Notably, BLOC1S5 loss-of-function produces distinct neurobiological phenotypes compared to other BLOC-1 subunit mutations, affecting synaptic composition and NMDA receptor expression differently 4. Beyond HPS-11, BLOC1S5 expression is significantly upregulated following hydroxychloroquine treatment in melanocytes, suggesting therapeutic potential for pigmentation disorders 5. BLOC1S5 has also been identified as a biomarker in cervical pathology and ovarian cancer progression 67.