Hermansky-Pudlak syndrome with a novel genetic variant in HPS1 and subsequent accelerated pulmonary fibrosis: significance for phenocopy diseases

Clinical Features and Novel Genetic Variants Associated with Hermansky-Pudlak Syndrome

Hermansky-Pudlak syndrome (HPS) is a rare autosomal recessive syndromic form of albinism, characterized by oculocutaneous albinism (OCA) and other systemic complications. The purpose of this study was to investigate patients with HPS-associated gene mutations and describe associated ocular and extraocular phenotypes. Fifty-four probands clinically diagnosed as albinism were enrolled. Ophthalmic examinations and genetic testing were performed in all subjects. The phenotypic and genetic features were evaluated. HPS-associated gene mutation was identified in four of the patients with albinism phenotype. Clinically, photophobia, and nystagmus was detected in all (4/4) patients, and strabismus was found in one (1/4) patient. Fundus examination revealed fundus hypopigmentation and foveal hypoplasia in all (8/8) eyes. Eight novel causative mutations were detected in these four HPS probands. Five (62.5%, 5/8) of the mutations were nonsense, two of the mutations were missense (25%, 2/8), and one of the mutations was frameshift (12.5%, 1/8). All patients in our study carried compound heterozygous variants, and all these pathogenic variants were identified to be novel, with most (62.5%, 5/8) of the mutations being nonsense. Our results improved the understanding of clinical ocular features, and expanded the spectrum of known variants and the genetic background of HPS.

Hermansky-Pudlak syndrome: Mutation update

Hermansky-Pudlak syndrome (HPS) is a group of 10 autosomal recessive multisystem disorders, each defined by the deficiency of a specific gene. HPS-associated genes encode components of four ubiquitously expressed protein complexes: Adaptor protein-3 (AP-3) and biogenesis of lysosome-related organelles complex-1 (BLOC-1) through -3. All individuals with HPS exhibit albinism and a bleeding diathesis; additional features occur depending on the defective protein complex. Pulmonary fibrosis is associated with AP-3 and BLOC-3 deficiency, immunodeficiency with AP-3 defects, and gastrointestinal symptoms are more prevalent and severe in BLOC-3 deficiency. Therefore, identification of the HPS subtype is valuable for prognosis, clinical management, and treatment options. The prevalence of HPS is estimated at 1-9 per 1,000,000. Here we summarize 264 reported and novel variants in 10 HPS genes and estimate that ~333 Puerto Rican HPS subjects and ~385 with other ethnicities are reported to date. We provide pathogenicity predictions for missense and splice site variants and list variants with high minor allele frequencies. Current cellular and clinical aspects of HPS are also summarized. This review can serve as a manifest for molecular diagnostics and genetic counseling aspects of HPS.

Novel genetic variant of HPS1 gene in Hermansky-Pudlak syndrome with fulminant progression of pulmonary fibrosis: a case report

Background

Hermansky-Pudlak syndrome (HPS) is an autosomal recessive disorder that is associated with oculocutaneous albinism, bleeding diathesis, granulomatous colitis, and highly penetrant pulmonary fibrosis in some subtypes. Homozygous or compound heterozygous pathological variants in HPS1, HPS3, HPS4, and several other genes lead to clinical manifestation of the disease.

Case presentation

A 57-year-old female was admitted with congenital oculocutaneous albinism, thrombocytopathy and late-onset accelerated pulmonary fibrosis (first symptoms from age 50 onwards). Chest high-resolution computed tomography identified thickening of peribronchovascular interstitium, bronchiectasis, reticulations, honeycombing, ground glass opacities and lung parenchyma consolidations. HPS was clinically suspected. We performed whole exome sequencing (WES), a form of massive parallel sequencing, of proband-parents trio. Whole exome libraries were processed using KAPA Hyper Prep Kit, SeqCap EZ MedExome Enrichment Kit and HyperCap Bead Kit according to the SeqCap EZ HyperCap Workflow. The paired-end 2 × 75 bp sequencing was performed on the Illumina NextSeq 500 Sequencer (Illumina Inc., USA). Furthermore, obtained variants by WES were evaluated using a virtual panel of genes: HPS1, AP3B1, HPS3, HPS4, HPS5, HPS6, DTNBP1, BLOC1S3, and PLDN. We identified a compound heterozygous genotype in HPS1 gene in the proband. We identified a pathogenic frameshift variant c.1189delC; p.(Gln397Serfs*2), resulting in a premature stop codon. This variant has been previously associated with HPS. Furthermore, we characterized previously undescribed nonsense variant c.1507C > T; p.(Gln503*), resulting in a premature stop codon and mRNA degradation through nonsense-mediated decay. Sanger sequencing validated the presence of both variants and simultaneously confirmed the heterozygous carrier status of parents. Unfortunately, the patient died due to fulminant progression of pulmonary fibrosis 2 months after diagnostics.

Conclusions

Compound heterozygous mutations in HPS1 in the proband lead to disruption of HPS1 gene and clinical manifestation of HPS with severe pulmonary fibrosis. This case illustrates the need to consider HPS in differential diagnostics of pulmonary fibrosis. Pulmonary fibrosis is a common cause of death in HPS patients. Earlier diagnosis may enable better treatment for these patients.