What is Hermansky-Pudlak Syndrome?
Hermansky-Pudlak syndrome (HPS) is a rare autosomal recessive multisystem disorder characterized by the triad of oculocutaneous albinism, bleeding diathesis from platelet dysfunction, and in certain subtypes (particularly HPS-1, HPS-2, and HPS-4), progressive lethal pulmonary fibrosis. 1
Core Clinical Features
HPS results from defective biogenesis of lysosome-related organelles, leading to abnormalities in cellular granules similar to other granule disorders. The syndrome encompasses at least 10 genetic subtypes (HPS1-9, plus additional genes including AP3B1, AP3D1, BLOC1S3, BLOC1S6, and DTNBP1), all inherited in an autosomal recessive manner. 1, 2
Cardinal Manifestations
The three defining features present in all HPS patients are:
- Oculocutaneous albinism with iris transillumination, photosensitivity, and hypopigmentation affecting 100% of patients 3
- Bleeding diathesis from severe thrombocytopenia, thrombasthenia, or platelet storage pool deficiency causing easy bruising 2, 4
- Nystagmus and poor visual acuity universally present 3
Genotype-Phenotype Correlations
The specific HPS subtype determines which life-threatening complications will develop:
High-Risk Subtypes (HPS-1, HPS-4, AP3B1)
These subtypes carry the highest risk for pulmonary fibrosis, which is the leading cause of mortality. 1, 4 When pulmonary fibrosis occurs, it typically manifests in the third decade of life and progresses to respiratory failure. 1, 5
HPS-2 Specific Features
HPS-2 uniquely presents with severe neutropenia and recurrent infections in addition to the standard triad, distinguishing it from other subtypes. 2
Additional Systemic Manifestations
Beyond the classic triad, patients commonly experience:
- Gastrointestinal: Granulomatous colitis (similar to Crohn's disease) and gastroesophageal reflux disease affecting 62-69% of patients 1, 3, 4
- Pulmonary: Dyspnea on exertion (38-52%), wheezing in approximately one-third 3
- Cardiac: Palpitations reported by majority 3
- Autoimmune: Xerophthalmia, skin rashes, myalgia 3
- Neurologic: Imbalance, headaches/migraines, photophobia 3
- Immunodeficiency: Present in some subtypes 1
- Lysosomal ceroid lipofuscin accumulation 6
Epidemiology and Population Genetics
HPS is an orphan disease with worldwide prevalence of 1 in 500,000 to 1,000 individuals. 5 However, specific variants show marked population enrichment, particularly in Puerto Rican ancestry (1 in 1,800) and Ashkenazi Jewish populations. 1, 5
Diagnostic Approach
For suspected HPS, platelet electron microscopy and gene sequencing should be considered. 1 The diagnosis requires recognition of the characteristic albinism and bleeding history, followed by genetic confirmation.
When to Suspect HPS
Genetic testing should be considered in patients with:
- Oculocutaneous albinism plus bleeding tendency
- Young-onset pulmonary fibrosis (third decade) with albinism 1
- Family history suggestive of autosomal recessive inheritance
- Granulomatous colitis with albinism
Critical Clinical Implications for Morbidity and Mortality
Progressive pulmonary fibrosis and respiratory failure represent the leading cause of death in HPS-1 and HPS-4 patients. 4 This necessitates:
- Surveillance for interstitial lung disease with serial pulmonary function testing
- Early treatment with pirfenidone (antifibrotic therapy) 5
- Prompt referral to lung transplantation centers when pulmonary fibrosis develops 4, 5
The accelerated phase of hemophagocytic lymphohistiocytosis (HLH) can occur in HPS patients, presenting with high fever, hepatosplenomegaly, and pancytopenia, which is often fatal without aggressive chemotherapy and immunosuppression. 2
Prognosis and Functional Status
Despite the multisystem nature of HPS, most adult participants report functional independence. 3 However, this depends critically on the specific subtype and whether pulmonary fibrosis develops. The oculocutaneous albinism and visual impairments are permanent and not corrected by any current interventions.