Article

Letter to the Editor

Ann Lab Med 2024; 44(3): 299-302

Published online May 1, 2024 https://doi.org/10.3343/alm.2023.0375

Copyright © Korean Society for Laboratory Medicine.

Twins With an Identical Novel Mutation in ITGB3: A Case Report of Glanzmann Thrombasthenia–like Syndrome

Jaewoong Lee, M.D., Ph.D.1* , Jong-Mi Lee, M.D., Ph.D.2* , Hoon Seok Kim, M.D., Ph.D.2 , Jin Jung, M.D.2 , Yonggoo Kim, M.D., Ph.D.2 , Suk Young Park, M.D., Ph.D.3 , Myungshin Kim, M.D., Ph.D.2 , and Eunhee Han, M.D., Ph.D.4

1Department of Laboratory Medicine, Incheon St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea; 2Department of Laboratory Medicine, Seoul St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea; 3Department of Oncology-Hematology, Konyang University Hospital, Daejeon, Korea; 4Department of Laboratory Medicine, Daejeon St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea

Correspondence to: Myungshin Kim, M.D., Ph.D.
Department of Laboratory Medicine, Seoul St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Banpodaero 222, Seocho-gu, Seoul 06591, Korea
E-mail: microkim@catholic.ac.kr

Eunhee Han, M.D., Ph.D.
Department of Laboratory Medicine, Daejeon St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Banpodaero 222, Seocho-gu, Seoul 06591, Korea
E-mail: haniyes@catholic.ac.kr

*These authors equally contributed to this study.

Received: September 20, 2023; Revised: October 23, 2023; Accepted: December 8, 2023

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Dear Editor,

Inherited thrombocytopenias are a heterogeneous group of diseases. Of them, Glanzmann thrombasthenia (GT) is a rare, inherited, autosomal recessive platelet disorder with quantitative and/or qualitative abnormalities in integrin αIIbβ3 (also known as glycoprotein IIb/IIIa) caused by genetic defects in ITGA2B and ITGB3. As the αIIbβ3 complex is a receptor for fibrinogen required for platelet aggregation, platelets with defective αIIbβ3 fail to aggregate in response to stimuli [1]. In contrast to classic GT, the autosomal dominant type of GT, characterized by macrothrombocytopenia and platelet functional defects, has been rarely reported. These cases have been named Glanzmann thrombasthenia–like syndrome (GTLS) or ITGA2B/ITGB3-related thrombocytopenia [2]. We report a novel mutation in ITGB3 detected in twin brothers and their mother who were diagnosed as having GTLS. This study was conducted in accordance with the Declaration of Helsinki and was approved by the Institutional Review Board of Seoul and Daejeon St. Mary’s Hospitals, Seoul, Korea (DC23ZASI0071).

A 20-yr-old man was referred to the hematology clinic of Daejeon St. Mary’s Hospital because of low platelet count, which was accidentally discovered during a general examination in July 2022. His blood test revealed thrombocytopenia (51×109/L, reference interval (RI): 150–450×109/L) with increased mean corpuscular volume (11 fL, RI: 7–10 fL). Platelet anisocytosis was evident in blood smear preparations, and leukocyte inclusions were not observed (Fig. 1A). Clotting screening tests revealed normal prothrombin and activated partial thromboplastin times. The serum antiplatelet antibody test was negative. The patient had no bleeding or thrombotic symptoms other than occasional petechia. His twin brother and mother also presented with macrothrombocytopenia and occasional petechia (Fig. 1B). Therefore, clinical-grade exome sequencing using TruSight One expanded panel (Illumina, San Diego, CA, USA) and whole-genome sequencing utilizing the Korean National Project of Bio Big Data were performed on the patient and his brother, respectively. Both tests identified the same novel mutation in ITGB3 (NM_000212.3: c.2192T>G, [NP_000203.2:p.Leu731Arg]). No potentially causal genomic aberrations were observed in other genes. Maternal inheritance was confirmed via Sanger sequencing analysis (Fig. 1C).

Figure 1. Test results of this case, pedigree, and the locations of mutations in the integrin molecule. (A) Macrothrombocytopenia with normal leukocyte morphology (May–Grunwald–Giemsa staining, 1,000× magnification). (B) Pedigree and the patients’ platelet indices. (C) Sanger sequencing results (NM_000212.3: c.2192T>G, [NP_000203.2:p.Leu731Arg]). (D) Structure of the integrin αIIbβ3 transmembrane complex. Leu731Arg and previously reported mutations are indicated using colored balls. (E) Defective platelet aggregation was observed for all agonists, except ristocetin. (F) Reserved expression of CD41a (αIIb) on the platelet surface of the patient (red) compared with that in the normal control (blue).
Abbreviations: PLT, platelet; MPV, mean platelet volume.

This variant was classified as likely pathogenic based on the American College of Medical Genetics [3] and ClinGen rules (https://clinicalgenome.org/working-groups/sequence-variant-interpretation/), with PP3-strong (BayesDel: pathogenic), PM2-supporting (gnomAD: absent), and PP2-supporting (91.4% of missense variants: pathogenic). As shown in Fig. 1D, this mutation occurs in the transmembrane domain (TMD) of integrin β3. Specifically, this mutation entails the substitution of the hydrophobic leucine with a hydrophilic arginine. This charge reversal in the TMD of β3 may potentially impact helix conformation, integrin assembly, and signaling pathways [4].

To confirm the functional defect, platelet-rich plasma was obtained from all affected family members. Platelet aggregation was severely diminished in response to adenosine 5′-diphosphate, collagen, arachidonic acid, and epinephrine, but not ristocetin (Fig. 1E). Flow cytometry analysis showed slightly increased CD41a expression, probably because of increased platelet size (Fig. 1F).

Approximately 200 pathogenic ITGB3 variants, mostly involved in classic GT, have been reported. In the Korean population, c.1913+5G>T is a recurrent mutation caused by a founder effect [5]. However, only 10 cases of GTLS with heterozygous ITGB3 mutations have been reported, including our case (Table 1) [2, 6-10]. Most GTLS cases presented with minor to moderate degrees of macrothrombocytopenia, accompanied by a bleeding tendency. Of the nine previously reported mutations, five occurred in the TMD of integrin β3. A mutational study revealed that the TMD of integrin β3 is involved in integrin clustering to regulate outside-in signaling via lipid microdomain coalescence [9]. Outside-in signaling via the αIIbβ3 complex after fibrinogen engagement is an important component of platelet formation. As hydrophobic residues play a critical role in controlling helix tilt in the TMD [4], our patient’s variant, which introduces a charge reversal, may alter helix tilt. Consequently, this alteration may lead to disorientation of the αIIb and β3 helices.

Table 1 . Heterozygous ITGB3 mutations in inherited macrothrombocytopenia identified to date

StudyProband
(sex/age)
ITGB3 mutationPlatelet count×109/LBlood smearsClinical features
ExonDNAProteinProtein region
Chen, et al. (1992) [6]NA14Not statedp.(Ser752Pro)*ICDLife-long bleeding tendency
Ghevaret, et al. (2008) [7]M/4914c.2245G>Cp.(Asp723His)*salt bridge80Platelet anisocytosis and giant platelets
Gresele, et al. (2009) [8]F/3513c.2134+1G>Cp.(D647_E686del)*ECD26–79Large plateletsLife-long moderate/severe bleeding, mainly mucocutaneous
Jayo, et al. (2010) [9]F/4314c.2231T>Cp.(Leu718Pro)*TMD127Platelet anisocytosisFrequent mucocutaneous hemorrhages, menorrhagia, and two episodes of spontaneous intra-peritoneal bleeding
Nurden, et al. (2017) [10]F/3014c.2230_2232delCTCp.(Leu718del)*TMD100–120Platelet anisotropy with abnormal granular structuresSporadic mucocutaneous bleeding (epistaxis, gingival bleeding, menorrhagia)
Morais, et al. (2020) [2]F/5114NM_000212.2:c.2236A>Cp.Thr746Prop.(Thr720Pro)*TMD71Platelet anisocytosis and platelet macrocytosisEasy bruising and gingival bleeding
Morais, et al. (2020) [2]F/4514NM_000212.2:c.2243A>Cp.His748Prop.(His722Pro)*ICD95Platelet anisocytosis, platelet macrocytosis, and rare giant plateletsEasy bruising and abundant menstruation
Morais, et al. (2020) [2]F/3714NM_000212.2:c.2278C>Tp.Arg760Cysp.(Arg734Cys)*TMD95Platelet anisocytosis, platelet macrocytosis, and rare giant plateletsEasy bruising with minor trauma and occasional gingival bleeding
Morais, et al. (2020) [2]M/7414NM_000212.2:c.2245G>Cp.Asp749Hisp.(Asp723His)*salt bridge112Platelet anisocytosis and some giant plateletsGingival bleeding and easy bruising
Present studyM/2014NM_000212.3:c.2192T>Gp.Leu731Argp.(Leu705Arg)*TMD51Platelet anisocytosis and platelet macrocytosisNo hemorrhagic symptoms, occasional petechial symptoms

*We included the descriptions of variants used in the original publications, with the signal peptide, including sequences (26 residues), shown in parentheses.

Because of the lack of reference transcript data in the original publications, we were unable to provide transcript numbers for these nomenclatures.

Abbreviations: ICD, intracellular domain; ECD, extracellular domain; TMD, transmembrane domain.



Regarding macrothrombocytopenia, a previous study suggested a role for αIIbβ3 in megakaryocytopoiesis, and some novel but rare point mutations in either ITGA2B or ITGB3 were associated with altered platelet production and selective deficiencies in platelet function [1].

Because of the rare occurrence of IT, patients with inherited low platelet counts may be misdiagnosed as having autoimmune thrombocytopenia and may receive inappropriate therapy [7]. In our case, thrombocytopenia was detected in the patient’s mother during her first pregnancy, and she underwent platelet transfusions during her first cesarean section. However, in cases where patients lack the intact form of integrin, repeated exposure to donor platelet transfusion may lead to sensitization and anti-αIIbβ3 antibody formation. This case underscores the importance of a genetic approach for a definitive diagnosis of an inherited platelet disorder.

Lee J and Lee JM were responsible for directing the project, collecting the data, interpreting the results, and writing the manuscript. Kim HS and Jung J aided in clinical data interpretation. Kim Y provided critical feedback on the report. Park SY collected clinical data and organized the genetic counseling. Han E and Kim M conceived the study and provided overall direction and planning. All authors read and approved the final manuscript.

This research was supported by the Bio & Medical Technology Development Program of the National Research Foundation (NRF-2020M3E5D7085175), funded by the Ministry of Health and Welfare, Ministry of Science and ICT, Ministry of Trade Industry and Energy, Korea Disease Control and Prevention Agency (The National Project of Bio Big Data) and National Research Foundation (NRF-2020R1F1A1068437) funded by the Ministry of Science and ICT.

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