Hermansky-Pudlak syndrome due to BLOC-1 deficiency

Hermansky-Pudlak syndrome due to BLOC-1 deficiency encompasses a group of subtypes within Hermansky-Pudlak syndrome (HPS) caused by mutations in genes encoding components of the biogenesis of lysosome-related organelles complex 1 (BLOC-1). This includes HPS type 7 (DTNBP1 gene), HPS type 8 (BLOC1S3 gene), HPS type 9 (BLOC1S6/PLDN gene), HPS type 10 (AP3D1 gene), and HPS type 11 (BLOC1S5 gene). BLOC-1 is essential for the proper formation and trafficking of lysosome-related organelles, including melanosomes in skin and eyes and dense granules in platelets. Patients typically present with oculocutaneous albinism (reduced pigmentation of the skin, hair, and eyes), visual impairment including nystagmus and reduced visual acuity, and a bleeding diathesis due to platelet storage pool deficiency. The bleeding tendency results from absent or reduced platelet dense granules, leading to easy bruising, prolonged bleeding after injuries or surgery, and epistaxis. Unlike some other HPS subtypes (particularly HPS-1 and HPS-4), BLOC-1 deficiency subtypes are generally considered to have a milder clinical course and are typically not associated with pulmonary fibrosis or granulomatous colitis, though long-term data remain limited due to the rarity of these conditions. Some subtypes, particularly HPS-10 due to AP3D1 mutations, may present with additional neurological features including seizures and neurodevelopmental abnormalities. There is currently no cure for Hermansky-Pudlak syndrome due to BLOC-1 deficiency. Management is supportive and includes sun protection to reduce skin damage from UV exposure, ophthalmologic care for visual impairment, and precautions to manage bleeding risk. Desmopressin (DDAVP) or platelet transfusions may be used to control bleeding episodes. Patients should avoid aspirin and other medications that impair platelet function. Regular monitoring by a multidisciplinary team including dermatology, hematology, and ophthalmology is recommended.

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