Protein assays for diagnosis of Wiskott-Aldrich syndrome and X-linked thrombocytopenia

Higher Prevalence of Monogenic Cause Among Very Early Onset Inflammatory Bowel Disease in Children: Experience From a Tertiary Care Center From Northern India

BACKGROUND

Very early-onset inflammatory bowel disease (VEO-IBD) is generally defined as onset of IBD at <6 years of age. Up to 20% of VEO-IBD may have a monogenic cause; hence, next-generation sequencing is highly recommended for diagnostic accuracy. There remains a paucity of data on VEO-IBD and the proportion of monogeneic causes in South Asia. We analyzed our tertiary care center experience of monogenic VEO-IBD from Northern India and compared them with nonmonogenic VEO-IBD to find out the factors that differentiate monogenic from nonmonogenic VEO-IBD.

METHODS

All children (<18 years of age) diagnosed with IBD between January 2010 to July 2021 were analyzed along with the next-generation sequencing data and functional assays when available. Clinical features and outcomes between monogenic and nonmonogenic VEO-IBD were compared.

RESULTS

A total of 200 children with a median age of 15.3 (range, 0.17-17) years, 125 of whom were boys, were diagnosed to have IBD during the study period. VEO-IBD was seen in 48 (24%) children. Monogenic IBD was diagnosed in 15 (31%) children with VEO-IBD and 7.5% of all IBD cases. The causes of monogenic VEO-IBD included disorders of the immune system (including interleukin-10 receptor mutations) in 12 and epithelial barrier dysfunction in 3. Features that differentiated monogenic from nonmonogenic VEO-IBD were neonatal IBD, presence of perianal disease, IBD unclassified, history of consanguinity and sibling death, wasting, and stunting (P < .05). There were 6 deaths.

CONCLUSIONS

One-third of participants were monogenic among Indian children with VEO-IBD, the highest proportion reported to date in the world. Next-generation (either exome or whole genome) sequencing should be recommended in a subset of VEO-IBD with neonatal onset, perianal disease, history of consanguinity and siblings' death, wasting, stunting, and IBD unclassified phenotype for an early diagnosis and referral to an appropriate center for hematopoietic stem cell transplantation for a better outcome.

Rapid Multiplexed Proteomic Screening for Primary Immunodeficiency Disorders From Dried Blood Spots

Background: Primary immunodeficiency disorders (PIDD) comprise a group of life-threatening congenital diseases characterized by absent or impaired immune responses. Despite the fact that effective, curative treatments are available with optimal clinical outcomes when diagnosed early, newborn screening does not exist for the majority of these diseases due to the lack of detectable, specific biomarkers or validated methods for population-based screening. Peptide immunoaffinity enrichment coupled with selected reaction monitoring mass spectrometry (immuno-SRM) is a sensitive proteomic assay, involving antibody-mediated peptide capture, that allows for concurrent quantification of multiple analytes. This assay has promise for use in potential newborn screening of PIDDs that lead to diminished or absent target proteins in the majority of cases. Objective: To determine and evaluate if a multiplex assay based on immuno-SRM is able to reliably and precisely distinguish affected patients with X-linked agammaglobulinemia (XLA), Wiskott-Aldrich Syndrome (WAS), and CD3ϵ-associated severe combined immunodeficiency (SCID) from one another and from unaffected normal control dried blood spot (DBS) samples. Methods: We performed a blinded, multiplexed analysis of proteolytically-generated peptides from WASp, BTK, and CD3ϵ (for WAS, XLA, and SCID, respectively) in DBS samples from 42 PIDD patients, 40 normal adult controls, and 62 normal newborns. The peptide ATPase copper transporting protein (ATP7B) 1056 was simultaneously monitored for quality assurance purposes. Results: The immuno-SRM assays reliably quantified the target peptides in DBS and accurately distinguished affected patients from normal controls. Analysis of signature peptides found statistically significant reduction or absence of peptide levels in affected patients compared to control groups in each case (WASp and BTK: p = 0.0001, SCID: p = 0.05). Intra and inter-assay precision ranged from 11 to 22% and 11 to 43% respectively; linearity (1.39-2000 fmol peptide), and stability (≤ 0.09% difference in 72 h) showed high precision for the multiplexed assay. Inter-laboratory assay comparison showed high concordance for measured peptide concentrations, with R² linearity ≥ 0.97 for the WASp 274, CD3ϵ 197, BTK 407, and ATP7B 1056 peptides. Conclusion: Immuno-SRM-based quantification of proteotypic peptides from WASp, BTK, and CD3ϵ in DBS distinguishes relevant PIDD cases from one another and from controls, raising the possibility of employing this approach for large-scale multiplexed newborn screening of selective PIDDs.

Inherited Macrothrombocytopenia: Correlating Morphology, Epidemiology, Molecular Pathology and Clinical Features

Inherited macrothrombocytopenia is increasingly being recognized as a relatively common condition. This descriptive review aims at focusing on the different areas of advancement that have taken place with this condition with particular reference to India. A pubmed search of articles between January 1990 and October 2017 with the key words-macrothrombocytopenia, asymptomatic macrothrombocytopenia, macrothrombocytopenia India, syndromic macrothrombocytopenia, molecular pathology, megakaryopoiesis and platelet formation were searched. The shortlisted articles were then read. Review articles provided additional references and the articles thus obtained were also read. Special interest and research conducted by the authors provided further sources of information. A total of 487 articles were found of which 68 articles were related to our subject of review. Review articles were read and additional articles from the reference quoted. Forty-four percent of nonsyndromic Inherited macrothrombocytopenia showed mutations of MYH9, GP1BB, GP1Ba, GPIX, ABCG5 and 8, ACTN, FLI, TUBB and RUNX1 frequently in heterozygous state. All types of inheritance pattern namely autosomal dominant, recessive and sex linked patterns have been described. Syndromic causes of this phenomenon are well known and have been described. Many asymptomatic patients do have mild or moderate bleeding history. Clinical algorithms to differentiate chronic ITP associated macrothrombocytopenia from inherited variety have been explored. Inherited macrothrombocytopenia is an emerging area of interest in platelet biology with its implication in diagnosis, prognosis, genetic counseling, management and in transfusion medicine.

Wiskott-Aldrich syndrome with macrothrombocytopenia

BACKGROUND

Wiskott-Aldrich syndrome is a rare X-linked immunodeficiency disorder with a variable phenotype.

CASE CHARACTERISTICS

3.5-year-old boy diagnosed with Wiskott-Aldrich syndrome.

OBSERVATION

Unusual and persistent thrombocytopenia with increased platelet volume (>10fL). He did not exhibit characteristic clinical and laboratory finding for the syndrome.

OUTCOME

Maternally inherited causative mutation in the exon 2 of the WAS gene was disclosed.

MESSAGE

This is a need for multidisciplinary assessment of patients with congenital or early infantile thrombocytopenia, including testing for mutations of the WAS gene in all unexplained cases even in the absence of characteristic microthrombocytopenia.

Tryptic peptide screening for primary immunodeficiency disease by LC/MS-MS

PURPOSE

Early diagnosis of primary immunodeficiency disorders (PIDDs) is critical for maximizing patient survival and clinical outcomes. Consequently, there is significant interest in developing broad-based, high-throughput, screening approaches capable of utilizing small blood volumes to identify patients with PIDD.

EXPERIMENTAL DESIGN

We developed a novel proteomic screening approach using tandem mass spectrometry to simultaneously identify specific signature peptides derived from the transmembrane protein cluster of differentiation 3 (CD3)ɛ and the intracellular proteins Wiskott-Aldrich syndrome protein (WASP) and Bruton's tyrosine kinase (BTK) as markers of three life-threatening PIDDs; severe combined immunodeficiency, Wiskott-Aldrich syndrome, and X-linked Agammaglobulinemia. Signature peptides were analyzed by LC/MS-MS in proteolytically digested lysates from cell lines and white blood cells (WBCs). The amount of each peptide was determined by the ratio of the signature peptide peak area to that of a known amount of labeled standard peptide. Peptide concentrations were normalized to actin.

RESULTS

We show that signature peptides from CD3ɛ, WASP, and BTK were readily detected in proteolytically digested cell lysate and their absence could correctly identify PIDD patients.

CONCLUSIONS AND CLINICAL RELEVANCE

This proof of concept study demonstrates the applicability of this approach to screen for PIDD and raises the possibility that it could be further multiplexed to identify additional PIDDs and potentially other disorders.

Wiskott-Aldrich syndrome presenting with a clinical picture mimicking juvenile myelomonocytic leukaemia

BACKGROUND

Wiskott-Aldrich syndrome (WAS) is a rare X-linked immunodeficiency caused by defects of the WAS protein (WASP) gene. Patients with WAS typically demonstrate micro-thrombocytopenia.

PROCEDURES

The report describes seven male infants with WAS that initially presented with leukocytosis, monocytosis, and myeloid and erythroid precursors in the peripheral blood (PB) and dysplasia in the bone marrow (BM), which was initially indistinguishable from juvenile myelomonocytic leukaemia (JMML).

RESULTS

The median age of affected patients was 1 month (range, 1-4 months). Splenomegaly was absent in four of these patients, which was unusual for JMML. A mutation analysis of genes in the RAS-signalling pathway did not support a diagnosis of JMML. Non-haematological features, such as eczema (n = 7) and bloody stools (n = 6), ultimately led to the diagnosis of WAS at a median age of 4 months (range, 3-8 months), which was confirmed by absent (n = 6) or reduced (n = 1) WASP expression in lymphocytes by flow cytometry (FCM) and a WASP gene mutation. Interestingly, mean platelet volume (MPV) was normal in three of five patients and six of seven patients demonstrated occasional giant platelets, which was not compatible with WAS.

CONCLUSIONS

These data suggest that WAS should be considered in male infants presenting with JMML-like features if no molecular markers of JMML can be detected.

Kaposi's sarcoma in a child with Wiskott-Aldrich syndrome

INTRODUCTION

Kaposi's sarcoma (KS) is rare in childhood. It may be favored by acquired immune deficiencies, but the predisposing factors to KS in other children are unclear.

DISCUSSION

KS has been reported in only two children and one adult with primary immunodeficiency. We report here a Tunisian child with a Wiskott-Aldrich syndrome who developed KS at the age of 14 months.

CONCLUSION

This observation expands the spectrum of primary immunodeficiencies associated with KS in childhood.

Immunological and genetic analysis of 65 patients with a clinical suspicion of X linked hyper-IgM

BACKGROUND

X linked hyper-IgM (XHIM) is a primary immunodeficiency caused by mutations in the tumour necrosis factor superfamily 5 gene, TNFSF5, also known as the CD40 ligand (CD40L) gene. Patients often present with recurrent infections, and confirmation of a diagnosis of XHIM enables appropriate therapeutic interventions, including replacement immunoglobulin, antibiotics, and bone marrow transplantation.

AIM

To review and optimise the institution's diagnostic strategy for XHIM.

METHOD

Samples from 65 boys were referred to this centre for further investigation of suspected XHIM. The results, which included a flow cytometric whole blood assay for CD40L expression followed by mutation analysis in selected patients, were reviewed.

RESULTS

Twenty one patients failed to express CD40L and TNFSF5 mutations were found in 20 of these patients. In contrast, no TNFSF5 mutations were found in 16 patients with weak expression of CD40L. Interestingly, one quarter of patients with confirmed XHIM who had TNFSF5 mutations had low concentrations of IgG, IgA, and IgM. Most of the remaining patients with XHIM had the classic pattern of normal or raised IgM with low concentrations of IgA and IgG.

CONCLUSIONS

This study demonstrates the usefulness of the whole blood staining method as a rapid screen to select patients for subsequent TNFSF5 mutation analysis, and shows the benefits of a unified protein/genetic diagnostic strategy.

Autoimmunity in Wiskott-Aldrich syndrome

As many as 40% of patients with Wiskott-Aldrich syndrome may eventually suffer from an autoimmune disorder, with an increased chance of developing a malignancy. Vasculitides and autoimmune hemolytic anemia are the two most common autoimmune manifestations and often cause considerable morbidity and mortality, because they may require treatment with bone marrow transplantation. Insights into the mechanisms of autoimmunity have provided clues to the pathogenesis of these disorders in Wiskott-Aldrich syndrome. Chronic inflammation, interleukin-2 deficiency, and increased apoptosis may all play a possible role in the loss of peripheral tolerance to self-antigens in this disease. This article reviews the manifestations and consequences of autoimmunity in Wiskott-Aldrich syndrome, its possible mechanisms, and available treatments.

The Wiskott-Aldrich syndrome protein: forging the link between actin and cell activation

The Wiskott-Aldrich syndrome protein (WASp) has emerged as a central player in the regulation of actin remodeling in T cells. The unique domain structure of WASp and other WASp family members enables these proteins to associate with a myriad of signaling effectors and to thereby regulate the coupling of T cell antigen receptor (TCR) engagement to both cytoskeletal rearrangement and transcriptional activation. This review focuses on these biochemical properties of WASp and also on the mechanisms whereby WASp interactions with its cognate ligands influence T cell activation. Because of its capacity to shift intracellular location and thereby dictate both the timing and the spatial distribution of actin polymerization following cell stimulation, WASp is well positioned to play major regulatory roles in directing a wide range of cellular processes and signaling pathways. Further dissection of the functional and biochemical properties of WASp therefore represents a promising avenue towards defining the molecular mechanisms that convey TCR stimulatory signals to the actin cytoskeleton and integrate cytoskeletal and other signaling systems so as to evoke a biological response.