PB1232 - Hermansky-Pudlak syndrome: Identification of novel variants in the genes HPS3, HPS5, and DTNBP1 (HPS-7) and analysis of lymphocyte cytotoxicity for the HPS-7 patient

Tuesday, July 12, 2022

6:30 PM – 7:30 PM

Location: Exhibition

Presentation Format: In-Person

Presenting Author(s)

Doris Boeckelmann, PhD

Research associate
Division of Pediatric Hematology and Oncology, Medical Center, Faculty of Medicine, University of Freiburg
Freiburg, Baden-Wurttemberg, Germany

Co-Author(s)

MW

Mira Wolter

Medical Graduate Student
Department of Pediatrics and Adolescent Medicine, Division of Pediatric Hematology and Oncology, Medical Center, Faculty of Medicine, University of Freiburg
Freiburg, Baden-Wurttemberg, Germany
KN

Katharina Neubauer

Research associate
Department of Pediatrics and Adolescent Medicine, Division of Pediatric Hematology and Oncology, Medical Center, Faculty of Medicine, University of Freiburg
Freiburg, Baden-Wurttemberg, Germany
Lukas J. Weiss

Clinical Scientist
University Hospital Wuerzburg
Würzburg, Bayern, Germany
HS

Harald Schulze

Chair of Experimental Biomedicine, University of Wuerzburg
Institute of Experimental Biomedicine, Chair I, University Hospital Würzburg
Würzburg, Bayern, Germany
FS

Felix Sobotta

Medical Graduate Student
Department of Pediatrics and Adolescent Medicine, Division of Pediatric Hematology and Oncology, Medical Center, Faculty of Medicine, University of Freiburg
Freiburg, Baden-Wurttemberg, Germany
AL

Antonia Lenz

Medical Graduate Student
Department of Pediatrics and Adolescent Medicine, Division of Pediatric Hematology and Oncology, Medical Center, Faculty of Medicine, University of Freiburg
Freiburg, Baden-Wurttemberg, Germany
HG

Hannah Glonnegger

Pediatric Resident Oncology and Hematology
Department of Pediatrics and Adolescent Medicine, Division of Pediatric Hematology and Oncology, Medical Center, Faculty of Medicine, University of Freiburg
Freiburg, Baden-Wurttemberg, Germany
BK

Barbara Käsmann-Kellner

Senior Physician
Department of Ophthalmology, Saarland University Medical Center
Homburg, Saarland, Germany
JM

Jasmin Mann

PhD student
Institute for Immunodeficiency, Center for Chronic Immunodeficiency (CCI), Medical Center – University of Freiburg, Faculty of Medicine
Freiburg, Baden-Wurttemberg, Germany
SE

Stephan Ehl

Director, Institute for Immunodeficiency, Center for Chronic Immunodeficiency (CCI)
Institute for Immunodeficiency, Center for Chronic Immunodeficiency (CCI), Medical Center – University of Freiburg, Faculty of Medicine
Freiburg, Baden-Wurttemberg, Germany
BZ

Barbara Zieger

Head of the Section Haemostaseology
Department of Pediatrics and Adolescent Medicine, Division of Pediatric Hematology and Oncology, Medical Center, Faculty of Medicine, University of Freiburg
Freiburg, Baden-Wurttemberg, Germany

Background: Hermansky-Pudlak syndrome (HPS) is characterized by oculocutaneous albinism (OCA) and bleeding diathesis (due to a defect regarding melanosomes and platelet δ-granule secretion). The disease-associated genes encode either for multi-protein complexes BLOC-1 - BLOC-3 (biogenesis of lysosome-related organelles complex) or for AP-3 (adaptor protein-3). Patients with HPS type 2 (HPS-2) or HPS-10 present additionally with an immunological defect. BLOC-2 deficiencies (genes: HPS3, HPS5, HPS6) seem to have milder phenotypes especially regarding albinism.

Aims: To characterize the platelet defect of three patients (Pt.1-3) who suffer from bleeding diathesis. Only patient 3 showed apparent OCA.

Methods: Platelet count, platelet aggregometry (LTA), and flow cytometry (FC). Mepacrine analysis and whole mount-transmission electronmicroscopy (WM-TEM) (Pt.1, Pt.3). Panel next-generation sequencing (NGS). Western blot analysis and analysis of lymphocyte cytotoxicity (Pt.3).

Results: Platelet aggregometry showed impaired platelet function. FC revealed a severely reduced CD63 expression (hinting to δ-granule defect). Mepacrine uptake was profoundly impaired in the investigated patients implying lack of δ-granules as confirmed by WM-TEM. NGS identified a homozygous deletion of exon 6 in DTNBP1 for Pt.3. Western blot analysis confirmed the absence of the encoded protein dysbindin leading to the diagnosis HPS-7 (BLOC-1). Interestingly, this patient reported additionally recurrent bacterial infections. Analysis of lymphocyte cytotoxicity showed a slightly reduced NK degranulation previously documented in a more severe form in patients with HPS-2 or HPS-10. Pt.1 is carrier of compound heterozygous variants in the HPS3 gene (c.65C>G and c.1193G>A). A homozygous variant in HPS5 (c.760G>T) was identified in Pt.2. The novel missense variants were classified as variants of uncertain significance according to ACMG guidelines. For Pt.1, a specialized ophthalmological examination showed ocular albinism.

Conclusion(s): NGS can facilitate the process of identifying the genetic defects regarding the different HPS subtypes (even with mild clinical phenotype). Analysis of lymphocyte cytotoxicity in a patient with BLOC-1 deficiency showed a slightly reduced NK degranulation.