Intermittent X-linked thrombocytopenia with a novel WAS gene mutation

Mutational Landscape of Patients with Wiskott Aldrich Syndrome: Update from India

PURPOSE

Wiskott-Aldrich syndrome (WAS) is an X-linked genetic disorder characterized by distinctive features including microthrombocytopenia, eczema and recurrent infections. In the present study we report clinical, immunological and molecular spectrum of 41 WAS patients diagnosed over last five years.

METHODS

Clinical and family history was collected from case records. Comprehensive immunological assessments including lymphocyte subset analysis, and flow cytometry based evaluation of WAS protein (WASP) expressions were performed in patients along with evaluation of carrier status in mothers. Genetic analysis was carried out with either Sanger sequencing or targeted exome sequencing.

RESULTS

The patients included in this study presented at a median age of 9.5 months, with two adult cases. Clinical manifestations encompassed thrombocytopenia, eczema, bleeding, diarrhea, respiratory tract infections, CMV infection, and malignancy. Immunological phenotype revealed T cell lymphopenia, B cell lymphopenia, and elevated IgE levels. Flow cytometry analysis of WASP was performed in 36 cases out of which 68.42% demonstrated complete absent expression while others showed reduced expression. Genetic analysis highlighted that the majority of mutations affect the WH1 domain of WASP while both adult patients showed intronic mutations. Molecular Dynamics analysis conducted for the novel variants P398R and G33R showed an average RMSD (Å) higher than that of the wild type, indicating greater structural perturbations in WASP.

CONCLUSION

In the present study we have documented 56.09% novel WAS mutations in Indian cohort. Notably, the application of flow cytometry has emerged as a valuable and efficient diagnostic tool for identifying these WAS patients.

Identification of a novel WAS mutation and the non-splicing effect of a second-site mutation in a Chinese pedigree with Wiskott-Aldrich syndrome

BACKGROUND

Wiskott-Aldrich syndrome (WAS) is a rare X-linked immunodeficiency disorder caused by abnormal expression of the WAS protein (WASp) due to mutations in the WAS gene, and is generally characterized by microthrombocytopenia, eczema, recurrent infections, and high susceptibility to autoimmune complications and hematological malignancies.

RESULTS

Herein, we identified a novel WAS mutation (c.158 T > C) using next-generation sequencing in a Chinese pedigree with WAS. The expression of WASp in the patients and their families was detected by flow cytometry and western blot analysis. To explore the exon-splicing effect of intron mutations and the correlation between the genotype and clinical phenotype, four groups of wild-type (WT), exon mutant, intron mutant, and combined mutant recombinant plasmids were transfected into COS-7 cells in vitro. The proband showed dramatically decreased WASp expression, while the female carriers showed a slightly lower level of WASp. The expression of products in the mutant and WT recombinant plasmids was detected by real-time fluorescence quantitative polymerase chain reaction (PCR), which showed a significant reduction in the combined mutant group than in the WT, exon mutant, and intron mutant groups. The length of the expression products in the four groups showed no differences, each containing 360 base pairs. Sequence analysis confirmed that the c.158 T > C mutation appeared in the exon mutant and combined mutant groups, whereas the intron variant c.273 + 14C > T caused no other sequence changes.

CONCLUSION

This study confirmed that the intron mutation did not affect the splicing of exons and excluded the influence of the double mutations at the transcription level on the severe clinical manifestations in the cousin. This in vitro study provided new insights into the pathogenesis of intronic mutations in WAS.

Diagnosis and clinical management of Wiskott-Aldrich syndrome: current and emerging techniques

INTRODUCTION

Wiskott-Aldrich syndrome (WAS) serves as the prototype of how variants in a gene which encodes a protein central to actin cytoskeletal homeostasis can manifest clinically in a variety of ways including infection, atopy, autoimmunity, inflammation, bleeding, neutropenia, non-malignant lymphoproliferation, and malignancy. Despite the discovery of the WAS gene almost 30 years ago, our understanding of the pathophysiological mechanisms underlying WAS continues to unfold.

AREAS COVERED

This review will provide an overview of the approach to the diagnosis of WAS as well as the management of its associated complications. Advances in the use of allogeneic hematopoietic stem cell transplantation (HSCT) and gene therapy as well as the associated challenges unique to WAS will be discussed.

EXPERT OPINION

Basic research, combined with clinical research focusing on longitudinal analysis of WAS patients, will help clarify determinants that influence WAS pathogenesis as well as clinical complications and outcomes. Advances in curative approaches including the use of alternative donor HSCT for WAS continue to evolve. Gene therapy employing safer and more effective protocols ensuring full correction of WAS will provide life-saving benefit to WAS patients that are unable to undergo HSCT.

Whole Wiskott‑Aldrich syndrome protein gene deletion identified by high throughput sequencing

Wiskott‑Aldrich syndrome (WAS) is a rare X‑linked recessive immunodeficiency disorder, characterized by thrombocytopenia, small platelets, eczema and recurrent infections associated with increased risk of autoimmunity and malignancy disorders. Mutations in the WAS protein (WASP) gene are responsible for WAS. To date, WASP mutations, including missense/nonsense, splicing, small deletions, small insertions, gross deletions, and gross insertions have been identified in patients with WAS. In addition, WASP‑interacting proteins are suspected in patients with clinical features of WAS, in whom the WASP gene sequence and mRNA levels are normal. The present study aimed to investigate the application of next generation sequencing in definitive diagnosis and clinical therapy for WAS. A 5 month‑old child with WAS who displayed symptoms of thrombocytopenia was examined. Whole exome sequence analysis of genomic DNA showed that the coverage and depth of WASP were extremely low. Quantitative polymerase chain reaction indicated total WASP gene deletion in the proband. In conclusion, high throughput sequencing is useful for the verification of WAS on the genetic profile, and has implications for family planning guidance and establishment of clinical programs.

Intermittent low platelet counts hampering diagnosis of X-linked thrombocytopenia in children: report of two unrelated cases and a novel mutation in the gene coding for the Wiskott-Aldrich syndrome protein

Background

Thrombocytopenia can occur in different circumstances during childhood and although immune thrombocytopenia is its most frequent cause, it is important to consider other conditions, especially when there is a persistent or recurrent low platelet count. We report two cases of intermittent thrombocytopenia, previously misdiagnosed as immune thrombocytopenia.

Cases presentation

Both cases described were boys who presented with an intermittent pattern of thrombocytopenia, with a persistently low mean platelet volume. In both patients, peripheral blood smear revealed small platelets and flow cytometry showed low expression of Wiskott-Aldrich syndrome protein (WASP) in leucocytes. Molecular analysis of the first case identified a mutation in exon 2 of the gene coding for WASP, leading to a p.Thr45Met amino acid change and confirming the diagnosis of X-linked thrombocytopenia. In the second case, a novel missense mutation in exon 2 of the gene coding for WASP was detected, which resulted in a p.Pro58Leu amino acid change.

Conclusion

These two rare presentations of thrombocytopenia highlight the importance of evaluating the peripheral blood smear in the presence of recurrent or persistent thrombocytopenia and show that failing to do so can lead to misdiagnoses. Since thrombocytopenia may be found in pediatric outpatient clinic, increased awareness among general pediatricians will help to improve the differential diagnosis of this condition.