Clinical and molecular insights into Glanzmann's thrombasthenia in China

Abstract

Glanzmann's thrombasthenia (GT) is a rare bleeding disorder characterized by spontaneous mucocutaneous bleeding. The disorder is caused by quantitative or qualitative defects in integrin αIIbβ3 (encoded by ITGA2B and ITGB3) on the platelet and is more common in consanguineous populations. However, the prevalence rate and clinical characteristics of GT in non-consanguineous populations have been unclear. We analyzed 97 patients from 93 families with GT in the Han population in China. This analysis showed lower consanguinity (18.3%) in Han patients than other ethnic populations in GT-prone countries. Compared with other ethnic populations, there was no significant difference in the distribution of GT types. Han females suffered more severe bleeding and had a poorer prognosis. We identified a total of 43 different ITGA2B and ITGB3 variants, including 25 previously unidentified, in 45 patients. These variants included 14 missense, 4 nonsense, 4 frameshift, and 3 splicing site variants. Patients with the same genotype generally manifested the same GT type but presented with different bleeding severities. This suggests that GT clinical phenotype does not solely depend on genotype. Our study provides an initial, yet important, clinical and molecular characterization of GT heterogeneity in China.

Keywords: Glanzmann's thrombasthenia; ethnic; platelet; variant; αIIbβ3.

Conflict of interest statement

Conflict of Interest

All authors declare that they have no conflict of interest.

© 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Figures

Figure 1

Han females suffered more severe bleeding and had a poorer prognosis. (A) Comparison of male and female patient demographics: patient number, average bleeding score, the percentage of lethal cases, and the percentage of patients experiencing relief with age. Six female relatives of proband (GT12, GT17a, GT18, GT27, GT43) died of hemorrhage. (B) Column diagram shows percentage of female patients with high bleeding scores greater than male patients. (high: bleeding score > or = 3, low: bleeding score

Figure 2

Most GT patients in the Han population were compound heterozygous. (A) Circle diagram shows the ratio of all identified mutations in ITGA2B and ITGB3, including the percentage of missense and nonsense mutations, deletions, frameshift, and splice site mutations. (B) Column diagram shows the number of clinically diagnosed GT patients who harbor different types of ITGA2B or ITGB3 mutations.

Figure 3

Forty-three different pathogenic variants were identified in 45 GT patients, of which 25 were new and 4 were recurrent pathogenic variants, showing genetic diversity in the Han population. (A) Schematic shows the ITGA2B DNA and αIIb domain structure. Variants are designated as a symbol according to their type and grouped to the nearest exon. Solic circle: nonsense variant. Curve: frameshift variant. Solic triangle: deletion variant. Hollow triangle: missense variant. Hollow diamond: splicing variant. Red: recurrent variant. Blue: novel variant. SP: signal peptide. TM: transmembrane domain. CD: cytoplasmic domain. (B) Schematic shows the ITGB3 DNA and β3 domain structure. Variants are designated as a symbol according to their type and grouped to the nearest exon. Solic circle: nonsense variant. Curve: frameshift variant. Hollow triangle: missense variant. Hollow diamond: splicing variant. Red: recurrent variant. Blue: novel variant. SP: signal peptide. TM: transmembrane domain. CD: cytoplasmic domain.

Figure 4

Characterization of a unique patient (GT39) with C857F and R590Q variants in ITGA2B. (A) Diagram depicting the C857-C911 disulfide bond within the integrin αIIbβ3 complex. GPIIb (136.5 kDa) is formed by two subunits, α (GPIIbα, 114 kDa), and β (GPIIbβ, 22.5 kDa), joined by a single disulfide bridge between GPIIbβ Cys-911 and GPIIba Cys-857. (B) Platelet aggregation analysis of GT39 by stimulation with ADP relative to a healthy individual (control). (C) Glycoprotein expression levels on platelet surfaces analyzed by flow cytometry. Shadow: control. Black line: GT39. Numbers are mean fluorescence intensity. (D) PAC-1 binding analysis on platelet surfaces with or without stimulation with thrombin by flow cytometry. Shadow: control. Black line: GT39. Numbers are mean fluorescence intensity. (E) αIIb R590 and αIIb C857 are highly conserved among species.