Hermansky-Pudlak syndrome due to BLOC-3 deficiency

Hermansky-Pudlak syndrome due to BLOC-3 deficiency encompasses subtypes HPS-1 and HPS-4 of Hermansky-Pudlak syndrome (HPS), caused by mutations in genes encoding components of the biogenesis of lysosome-related organelles complex 3 (BLOC-3). Specifically, HPS-1 is caused by mutations in the HPS1 gene and HPS-4 by mutations in the HPS4 gene. BLOC-3 is essential for the proper formation and function of lysosome-related organelles, including melanosomes in skin and eyes, dense granules in platelets, and lamellar bodies in lung epithelial cells. Deficiency of this complex leads to the classic and often most severe forms of Hermansky-Pudlak syndrome. Patients typically present with oculocutaneous albinism (reduced pigmentation of the skin, hair, and eyes), nystagmus, reduced visual acuity, and a bleeding diathesis due to platelet storage pool deficiency. The bleeding tendency manifests as easy bruising, prolonged bleeding after injuries or surgery, epistaxis, and heavy menstrual bleeding in women. A particularly serious complication associated with BLOC-3 deficiency is pulmonary fibrosis, which typically develops in the third to fourth decade of life and is a major cause of morbidity and mortality. Some patients may also develop granulomatous colitis resembling Crohn's disease. There is currently no cure for Hermansky-Pudlak syndrome due to BLOC-3 deficiency. Management is supportive and multidisciplinary, including sun protection, visual aids, and avoidance of medications that impair platelet function (such as aspirin). Desmopressin (DDAVP) or platelet transfusions may be used to manage bleeding episodes. Pulmonary fibrosis is monitored with serial pulmonary function tests and high-resolution CT scans; pirfenidone has been investigated as a potential treatment for the lung disease. Lung transplantation may be considered in advanced cases. HPS-1 due to BLOC-3 deficiency is particularly prevalent in northwestern Puerto Rico due to a founder mutation.

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