HPS4 gene

• Overview
• Albinism
• Additional information
• References

Overview

Gene (OMIM No.)	HPS4 (#606682)
Function of gene/protein	Protein: subunit 2 of the biogenesis of lysosome-related organelles complex-3 (BLOC-3) BLOC-3 complex plays an important role in the control of melanin production and melanosome biogenesis by promoting membrane recruitment of specific Rab GTPases (Rab32 and Rab38)
Clinical phenotype (OMIM phenotype no.)	Hermansky-Pudlak syndrome 4 (#614073)
Inheritance	Autosomal recessive
Ocular features	Albinism Intra- and interfamilial variability in disease severity
Systemic features	Skin and hair depigmentation Bleeding diathesis due to platelet storage pool deficiency (easy/prolonged bleeding, easy bruising, prolonged/heavy menorrhagia, epistaxis) At risk of developing pulmonary fibrosis (onset usually during early 30s) and granulomatous colitis
Key investigations	Orthoptic assessment and refraction OCT to detect foveal hypoplasia Visual evoked potentials to detect evidence of chiasmal misrouting Eye movement recordings Systemic assessment with a pediatrician, haematologists and other relevant specialists
Molecular diagnosis	Next generation sequencing Targeted gene panels (albinism) Whole exome sequencing Whole genome sequencing
Management	Ocular Management of albinism Systemic Multidisciplinary approach
Therapies under research	A phase 2 randomised controlled trial of oral pirfenidone (an antifibrotic drug) for HPS1 and HPS4 associated pulmonary fibrosis showed equivocal results between placebo and intervention arms
Further information	Medline Plus

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Additional information

Hermansky-Pudlak syndrome (HPS) patients with BLOC-3 defects (HPS1 or HPS4) have more severe ocular and systemic phenotypes compared to those with BLOC-2 defects (HPS3, HPS5 and HPS6).^[2] 

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References

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