Wiskott-Aldrich syndrome in a female

Wiskott-Aldrich syndrome protein expression in female WAS carriers: A flow cytometry study from North India

INTRODUCTION

Wiskott-Aldrich syndrome (WAS) is a rare X-linked inborn error of immunity characterized by microthrombocytopenia, infections, eczema, and increased predisposition to develop autoimmunity and malignancy. Flow cytometric assay for determining WAS protein (WASp) is a rapid and cost-effective tool for detecting patients. However, very few studies described WASp expression in female carriers. Most WAS carriers are clinically asymptomatic. Active screening of female family members helps identify female carriers, distinguish de novo mutations, and to select appropriate donor prior to curative stem cell transplantation. This study was undertaken to evaluate the diagnostic capability of flow cytometry-based WASp expression in peripheral blood cells to identify carriers and compare WASp expression in different blood cell lineages.

PATIENTS AND METHODS

Female patients, heterozygous for WAS gene, were enrolled in this study conducted at Pediatric Allergy Immunology Unit, Advanced Pediatric Centre, Post Graduate Institute of Medical Education and Research, Chandigarh, India. Flow cytometric assessment of WASp expression in lymphocytes, monocytes, and neutrophils was carried out and compared with healthy control and affected patients. The results were expressed in delta (Δ) median fluorescence intensity (MFI) as well as stain index (SI), which is the ratio of ΔMFI of patient and ΔMFI of control.

RESULTS

Thirteen mothers and two sisters of genetically confirmed WAS patients were enrolled in the study. All enrolled females were clinically asymptomatic and did not have microthrombocytopenia. Low WASp expression (SI < 1) was seen in lymphocytes and monocytes in 10 (66.6%) carriers. Females with variants in proximal exons (exons 1 and 2) were found to have lesser expression than those with distal (exons 3-12) variants.

CONCLUSION

Flow cytometry is a rapid, easily available, cost-effective tool for WASp estimation. Lymphocytes followed by monocytes are the best cell lineages for WASp estimation in carrier females. However, genetic testing remains the gold standard, as carrier females with variants in distal exons may have normal WASp expression.

From Mendel to mycoses: Immuno-genomic warfare at the human-fungus interface

Fungi are opportunists: They particularly require a defect of immunity to cause severe or disseminated disease. While often secondary to an apparent iatrogenic cause, fungal diseases do occur in the absence of one, albeit infrequently. These rare cases may be due to an underlying genetic immunodeficiency that can present variably in age of onset, severity, or other infections, and in the absence of a family history of disease. They may also be due to anti-cytokine autoantibodies. This review provides a background on how human genetics or autoantibodies underlie cases of susceptibility to severe or disseminated fungal disease. Subsequently, the lessons learned from these inborn errors of immunity marked by fungal disease (IEI-FD) provide a framework to begin to mechanistically decipher fungal syndromes, potentially paving the way for precision therapy of the mycoses.

Biallelic variants in RBM42 cause a multisystem disorder with neurological, facial, cardiac, and musculoskeletal involvement

Here, we report a previously unrecognized syndromic neurodevelopmental disorder associated with biallelic loss-of-function variants in the RBM42 gene. The patient is a 2-year-old female with severe central nervous system (CNS) abnormalities, hypotonia, hearing loss, congenital heart defects, and dysmorphic facial features. Familial whole-exome sequencing (WES) reveals that the patient has two compound heterozygous variants, c.304C>T (p.R102*) and c.1312G>A (p.A438T), in the RBM42 gene which encodes an integral component of splicing complex in the RNA-binding motif protein family. The p.A438T variant is in the RRM domain which impairs RBM42 protein stability in vivo. Additionally, p.A438T disrupts the interaction of RBM42 with hnRNP K, which is the causative gene for Au-Kline syndrome with overlapping disease characteristics seen in the index patient. The human R102* or A438T mutant protein failed to fully rescue the growth defects of RBM42 ortholog knockout ΔFgRbp1 in Fusarium while it was rescued by the wild-type (WT) human RBM42. A mouse model carrying Rbm42 compound heterozygous variants, c.280C>T (p.Q94*) and c.1306_1308delinsACA (p.A436T), demonstrated gross fetal developmental defects and most of the double mutant animals died by E13.5. RNA-seq data confirmed that Rbm42 was involved in neurological and myocardial functions with an essential role in alternative splicing (AS). Overall, we present clinical, genetic, and functional data to demonstrate that defects in RBM42 constitute the underlying etiology of a new neurodevelopmental disease which links the dysregulation of global AS to abnormal embryonic development.

Síndrome de Wiskott-Aldrich en España: incidencia, mortalidad y sesgo de género durante 21 años

Antecedentes

El síndrome de Wiskott-Aldrich (SWA) es un raro trastorno ligado al cromosoma X que se considera que afecta predominantemente a varones.

Objetivo

El objetivo de este estudio consistía en investigar la incidencia y la mortalidad intrahospitalaria del SWA en España, así como el sesgo de género.

Métodos

Se llevó a cabo un estudio epidemiológico retrospectivo poblacional en 97 pacientes con SWA diagnosticados en hospitales españoles entre 1997 y 2017, utilizando para ello datos del Sistema Nacional de Vigilancia de Datos Hospitalarios.

Resultados

Nuestros resultados revelaron que la incidencia anual media del SAW en España fue de 1,1 caso por cada 10 millones de habitantes (IC del 95 %, 0,45-2,33). El riesgo relativo fue mayor en los varones que en las mujeres (2,42). El diagnóstico de SWA se establece a una edad más avanzada en las mujeres (mediana de 47 años) que en los varones (mediana de 5,5 años). Únicamente los varones ingresaron en el hospital en al menos 10 ocasiones diferentes y todas las muertes se detectaron en varones. La tasa de mortalidad intrahospitalaria fue del 9,28 % en el SAW y la mayoría de las muertes se asociaron a hemorragia cerebral o infección.

Conclusiones

El SWA, una enfermedad rara, se diagnostica a una edad más avanzada en las mujeres y la mortalidad se observó exclusivamente en varones, asociada en la mayoría de los casos a hemorragia cerebral e infección.

Targeted RNAseq Improves Clinical Diagnosis of Very Early-Onset Pediatric Immune Dysregulation

Despite increased use of whole exome sequencing (WES) for the clinical analysis of rare disease, overall diagnostic yield for most disorders hovers around 30%. Previous studies of mRNA have succeeded in increasing diagnoses for clearly defined disorders of monogenic inheritance. We asked if targeted RNA sequencing could provide similar benefits for primary immunodeficiencies (PIDs) and very early-onset inflammatory bowel disease (VEOIBD), both of which are difficult to diagnose due to high heterogeneity and variable severity. We performed targeted RNA sequencing of a panel of 260 immune-related genes for a cohort of 13 patients (seven suspected PID cases and six VEOIBD) and analyzed variants, splicing, and exon usage. Exonic variants were identified in seven cases, some of which had been previously prioritized by exome sequencing. For four cases, allele specific expression or lack thereof provided additional insights into possible disease mechanisms. In addition, we identified five instances of aberrant splicing associated with four variants. Three of these variants had been previously classified as benign in ClinVar based on population frequency. Digenic or oligogenic inheritance is suggested for at least two patients. In addition to validating the use of targeted RNA sequencing, our results show that rare disease research will benefit from incorporating contributing genetic factors into the diagnostic approach.

Immunity and Genetics at the Revolving Doors of Diagnostics in Primary Immunodeficiencies

Primary immunodeficiencies (PIDs) are a large and growing group of disorders commonly associated with recurrent infections. However, nowadays, we know that PIDs often carry with them consequences related to organ or hematologic autoimmunity, autoinflammation, and lymphoproliferation in addition to simple susceptibility to pathogens. Alongside this conceptual development, there has been technical advancement, given by the new but already established diagnostic possibilities offered by new genetic testing (e.g., next-generation sequencing). Nevertheless, there is also the need to understand the large number of gene variants detected with these powerful methods. That means advancing beyond genetic results and resorting to the clinical phenotype and to immunological or alternative molecular tests that allow us to prove the causative role of a genetic variant of uncertain significance and/or better define the underlying pathophysiological mechanism. Furthermore, because of the rapid availability of results, laboratory immunoassays are still critical to diagnosing many PIDs, even in screening settings. Fundamental is the integration between different specialties and the development of multidisciplinary and flexible diagnostic workflows. This paper aims to tell these evolving aspects of immunodeficiencies, which are summarized in five key messages, through introducing and exemplifying five clinical cases, focusing on diseases that could benefit targeted therapy.

Wiskott Aldrich syndrome: healthcare utilizations and disparities in transplant care

Wiskott Aldrich syndrome (WAS) is a rare disease and hematopoietic stem cell transplant (HCT) is considered the treatment modality of choice for WAS. We conducted a cross-sectional analysis on the KIDS' pediatric inpatient database and compared hospitalization rates, complications and healthcare utilizations in the transplant and non-transplant arms. Of the 383 pediatric admissions with diagnosis of WAS between 2006-2012, 114 underwent transplant and 269 did not. The non-transplant arm included older children, female patients and more African Americans. Death rates, income and payer source were similar in both arms, however the total charge for each admission was higher in the transplant arm. Emergency room visits were similar but non-elective admissions were more in the non-transplant arm. Length of stay was prolonged in the transplant arm. When comparing morbidities, lymphomas, ulcerative colitis and autoimmune complications of WAS were seen only in the non-transplant arm. Our study shows that transplant is the largest contributor to healthcare utilization in WAS patients. We identified healthcare disparities based on race and socioeconomic status and found that this rare disease is being appropriately directed to centers with HCT expertise. We noted a change in practice moving away from splenectomy in WAS patients.

Neuropsychological Profile of a Girl with Wiskott-Aldrich Syndrome

We report the neuropsychological profile of a 6-year-old girl with Wiskott-Aldrich syndrome, a rare X-linked immunodeficiency disorder associated with thrombocytopenia, eczema, recurrent infections, and malignancy. Wiskott-Aldrich syndrome occurs almost exclusively in males and is extremely rare in females, with no known research focused on cognitive and academic functioning in this population. Our patient was referred due to concerns about her memory and academic functioning. She had a history of progressive thrombocytopenia and hematopoietic stem cell transplantation at age 15 months. Standardized measures of intellectual ability, language, visual-spatial and visual-motor skills, attention, memory, and academic achievement were administered. The results showed average to above-average performance in multiple areas of cognitive and academic functioning, with weaknesses in phonological awareness and rapid naming. The advent of hematopoietic stem cell transplantation has led to considerable improvement in the long-term prognosis of children with Wiskott-Aldrich syndrome. Although the impact of this syndrome and related conditions on neurocognitive development is presently unknown, this case highlights both the importance of considering base rates for commonly occurring conditions and the significant role neuropsychology can play in identifying cognitive strengths and weaknesses in the context of the developing brain.

Whole-exome sequencing for detecting inborn errors of immunity: overview and perspectives

The study of inborn errors of immunity is based on a comprehensive clinical description of the patient’s phenotype and the elucidation of the underlying molecular mechanisms and their genetic etiology. Deciphering the pathogenesis is key to genetic counseling and the development of targeted therapy. This review shows the power of whole-exome sequencing in detecting inborn errors of immunity along five central steps taken in whole-exome sequencing analysis. In parallel, we highlight the challenges for the clinical and scientific use of the method and how these hurdles are currently being addressed. We end by ruminating on major areas in the field open to future research.

Periodontal and other oral manifestations of immunodeficiency diseases

The list of immunodeficiency diseases grows each year as novel disorders are discovered, classified, and sometimes reclassified due to our ever-increasing knowledge of immune system function. Although the number of patients with secondary immunodeficiencies (SIDs) greatly exceeds those with primary immunodeficiencies (PIDs), the prevalence of both appears to be on the rise probably because of scientific breakthroughs that facilitate earlier and more accurate diagnosis. Primary immunodeficiencies in adults are not as rare as once thought. Globally, the main causes of secondary immunodeficiency are HIV infection and nutritional insufficiencies. Persons with acquired immune disorders such as AIDS caused by the human immunodeficiency virus (HIV) are now living long and fulfilling lives as a result of highly active antiretroviral therapy (HAART). Irrespective of whether the patient's immune-deficient state is a consequence of a genetic defect or is secondary in nature, dental and medical practitioners must be aware of the constant potential for infections and/or expressions of autoimmunity in these individuals. The purpose of this review was to study the most common conditions resulting from primary and secondary immunodeficiency states, how they are classified, and the detrimental manifestations of these disorders on the periodontal and oral tissues.

WASP-WIP complex in the molecular pathogenesis of Wiskott-Aldrich syndrome

Wiskott-Aldrich syndrome (WAS) is an X-linked primary immunodeficiency disease characterized by recurrent infection, thrombocytopenia, and eczema. The gene responsible for X-linked WAS encodes the Wiskott-Aldrich syndrome protein (WASP), which is expressed in hematopoietic cells and which regulates T-cell activation and cytoskeletal reorganization in T-cell receptor (TCR) signaling. Here, I review my recent research on WASP and the WASP-interacting protein (WIP) complex in T cells. I and my colleagues first established a diagnostic screening method using flow cytometry and genetic analysis, and elucidated the molecular pathogenesis in WAS patients with unique clinical manifestations. We investigated the mechanisms by which WASP is recruited to lipid rafts following TCR stimulation and to immunological synapses between antigen-presenting cells and T cells. Subsequently, we elucidated the molecular mechanisms by which WASP is degraded by calpain and ubiquitinated by Cbl-family proteins, which terminate WASP activation. More importantly, we found that WIP plays a critical role in WASP stability in T cells. These results provide new insights into the molecular pathogenesis of X-linked WAS and have facilitated the identification of WIP deficiency as an autosomal recessive form of WAS.

Practice parameter for the diagnosis and management of primary immunodeficiency

The American Academy of Allergy, Asthma & Immunology (AAAAI) and the American College of Allergy, Asthma & Immunology (ACAAI) have jointly accepted responsibility for establishing the "Practice parameter for the diagnosis and management of primary immunodeficiency." This is a complete and comprehensive document at the current time. The medical environment is a changing environment, and not all recommendations will be appropriate for all patients. Because this document incorporated the efforts of many participants, no single individual, including those who served on the Joint Task Force, is authorized to provide an official AAAAI or ACAAI interpretation of these practice parameters. Any request for information about or an interpretation of these practice parameters by the AAAAI or ACAAI should be directed to the Executive Offices of the AAAAI, the ACAAI, and the Joint Council of Allergy, Asthma & Immunology. These parameters are not designed for use by pharmaceutical companies in drug promotion.

Severe and moderate haemophilia A and B in US females

Haemophilia A and B are rare X-lined hemorrhagic disorders that typically affect men. Women are usually asymptomatic carriers, but may be symptomatic and, rarely, also express severe (factor VIII (FVIII) or factor IX (FIX) <0.01 U mL(-1)) or moderately severe (FVIII/FIX 0.01-0.05 U mL(-1)) phenotypes. However, data on clinical manifestations, genotype and the psychosocial ramifications of illness in severely affected females remain anecdotal. A national multi-centre retrospective study was conducted to collect a comprehensive data set on affected US girls and women, and to compare clinical observations to previously published information on haemophilic males of comparable severity and mildly affected haemophilic females. Twenty-two severe/moderate haemophilia A/B subjects were characterized with respect to clinical manifestations and disease complications; genetic determinants of phenotypic severity; and health-related quality of life (HR-QoL). Clinical data were compared as previously indicated. Female patients were older than male patients at diagnosis, but similarly experienced joint haemorrhage, disease- and treatment-related complications and access to treatment. Gynaecological and obstetrical bleeding was unexpectedly infrequent. F8 or F9 mutations, accompanied by extremely skewed X-chromosome inactivation pattern (XIP), were primary determinants of severity. HR-QoL was diminished by arthropathy and viral infection. Using systematic case verification of participants in a national surveillance registry, this study elucidated the genetics, clinical phenotype and quality of life issues in female patients with severe/moderate haemophilia. An ongoing international case-controlled study will further evaluate these observations. Novel mechanistic questions are raised about the relationship between XIP and both age and tissue-specific FVIII and FIX expression.

A novel primary human immunodeficiency due to deficiency in the WASP-interacting protein WIP

A homozygous mutation that gave rise to a stop codon in the WIPF1 gene resulted in WASP protein destabilization and in symptoms resembling those of Wiskott-Aldrich syndrome

A female offspring of consanguineous parents, showed features of Wiskott-Aldrich syndrome (WAS), including recurrent infections, eczema, thrombocytopenia, defective T cell proliferation and chemotaxis, and impaired natural killer cell function. Cells from this patient had undetectable WAS protein (WASP), but normal WAS sequence and messenger RNA levels. WASP interacting protein (WIP), which stabilizes WASP, was also undetectable. A homozygous c.1301C>G stop codon mutation was found in the WIPF1 gene, which encodes WIP. Introduction of WIP into the patient’s T cells restored WASP expression. These findings indicate that WIP deficiency should be suspected in patients with features of WAS in whom WAS sequence and mRNA levels are normal.

DOCK8 is essential for T-cell survival and the maintenance of CD8+ T-cell memory

Deficiency in the guanine nucleotide exchange factor dedicator of cytokinesis 8 (DOCK8) causes a human immunodeficiency syndrome associated with recurrent sinopulmonary and viral infections. We have recently identified a DOCK8-deficient mouse strain, carrying an ethylnitrosourea-induced splice-site mutation that shows a failure to mature a humoral immune response due to the loss of germinal centre B cells. In this study, we turned to T-cell immunity to investigate further the human immunodeficiency syndrome and its association with decreased peripheral CD4(+) and CD8(+) T cells. Characterisation of the DOCK8-deficient mouse revealed T-cell lymphopenia, with increased T-cell turnover and decreased survival. Egress of mature CD4(+) thymocytes was reduced with increased migration of these cells to the chemokine CXCL12. However, despite the two-fold reduction in peripheral naïve T cells, the DOCK8-deficient mice generated a normal primary CD8(+) immune response and were able to survive acute influenza virus infection. The limiting effect of DOCK8 was in the normal survival of CD8(+) memory T cells after infection. These findings help to explain why DOCK8-deficient patients are susceptible to recurrent infections and provide new insights into how T-cell memory is sustained.

WASP: a key immunological multitasker

The Wiskott-Aldrich syndrome protein (WASP) is an important regulator of the actin cytoskeleton that is required for many haematopoietic and immune cell functions, including effective migration, phagocytosis and immune synapse formation. Loss of WASP activity leads to Wiskott-Aldrich syndrome, an X-linked disease that is associated with defects in a broad range of cellular processes, resulting in complex immunodeficiency, autoimmunity and microthrombocytopenia. Intriguingly, gain of function mutations cause a separate disease that is mainly characterized by neutropenia. Here, we describe recent insights into the cellular mechanisms of these two related, but distinct, human diseases and discuss their wider implications for haematopoiesis, immune function and autoimmunity.

X chromosome inactivation in clinical practice

X chromosome inactivation (XCI) is the transcriptional silencing of the majority of genes on one of the two X chromosomes in mammalian females. Females are, therefore, mosaics for two cell lines, one with the maternal X and one with the paternal X as the active chromosome. The relative proportion of the two cell lines, the X inactivation pattern, may be analyzed by simple assays in DNA from available tissues. This review focuses on medical issues related to XCI in X-linked disorders, and on the value of X inactivation analysis in clinical practice.

Evolution of highly polymorphic T cell populations in siblings with the Wiskott-Aldrich Syndrome

Population level evolutionary processes can occur within a single organism when the germ line contains a mutation that confers a cost at the level of the cell. Here we describe how multiple compensatory mutations arose through a within-individual evolutionary process in two brothers with the immune deficiency Wiskott-Aldrich Syndrome (WAS). As a result, both brothers have T lymphocyte populations that are highly polymorphic at the locus of the germ line defect, and no single allele achieves fixation. WASP, the gene product affected in this disease, is specific to white blood cells where it is responsible for regulating actin cytoskeleton dynamics in a wide range of cellular responses. The brothers inherited a rare allele predicted to result in truncated WASP lacking the carboxy-terminal VCA domains, the region that directly catalyzes actin filament generation. Although the brothers' T cell populations are highly polymorphic, all share a corrective effect relative to the inherited allele in that they restore the VCA domain. This indicates massive selection against the truncated germ line allele. No single somatic allele becomes fixed in the circulating T cell population of either brother, indicating that a regulated step in maturation of the affected cell lineage is severely compromised by the germ line allele. Based on the finding of multiple somatic mutations, the known maturation pathway for T-lineage cells and the known defects of T cells and precursor thymocytes in mice with truncated WASP, we hypothesize that the presence of truncated WASP (WASPΔVCA) confers an extreme disadvantage in early developing thymocytes, above and beyond the known cost of absence of full-length WASP, and that the disadvantage likely occurs through dominant negative competition of WASPΔVCA with N-WASP, a protein that otherwise partially compensates for WASP absence in developing thymocytes.

Clinical aspects and molecular analysis of Chinese patients with Wiskott-Aldrich syndrome in Taiwan

BACKGROUND

Wiskott-Aldrich syndrome (WAS) is an X-linked immunodeficiency, characterized by microthrombocytopenia, eczema and recurrent infections. More than 441 patient mutations have been described all over the world, mainly based on Caucasian and Japanese people. There have been few reported cases involving Chinese WAS patients.

OBJECTIVE

We investigated Chinese WAS patients in Taiwan since 1980.

METHODS

All WAS patients met the diagnosis criteria. Clinical manifestations, immunological functions, gene sequencing and the WAS protein (WASP) expression were analyzed.

RESULTS

Eleven male Chinese WAS patients were enrolled, presenting as classic WAS phenotype, correlative to the expression level of WASP and the severity of infections. Seven patients had autoimmune disorders, encompassing autoimmune hemolysis in 4, lymphoproliferative disorders in 2 and ulcerative colitis in 1 patient. As well as prophylactic monthly intravenous immunoglobulin infusion, splenectomy was performed on 2 patients. Five patients received hematopoietic stem cell transplantation. The causes of mortality were mass bleeding, sepsis and Epstein Barr virus-associated lymphoproliferative disorders in 3 nontransplant patients and acute graft failure and cytomegalovirus pneumonitis in 2 transplant patients. Nine patients received genetic analysis and revealed 4 unique mutations. None had the X-linked thrombocytopenia phenotype.

CONCLUSIONS

All of the recognized Chinese WAS patients had the classic phenotype. Most mutations involved exon 1 of the WASP gene and none had the X-linked thrombocytopenia phenotype. This may be attributable to genetic variation, although selection bias may exist.

A novel Wiskott-Aldrich syndrome protein (WASP) complex mutation identified in a WAS patient results in an aberrant product at the C-terminus from two transcripts with unusual polyA signals

Wiskott-Aldrich syndrome (WAS) is an X-linked recessive disorder characterized by immunodeficiency, thrombocytopenia and eczema. A broad spectrum of mutations in the WASP gene has been identified as causing the disease. In the present paper, we report on a patient affected by WAS with a novel complex mutation, characterized by a small 9 bp deletion followed by an inversion of 151 bp and a gross deletion of 4.3 kb within the Xp11.23 region. The small deletion and the inverted fragment are found in intron 11. The large deletion initiates downstream of exon 11 of the WASP gene, including exon 12, and a genomic region upstream of the promoter of the contiguous SUV39H1 gene. Expression studies of the mRNA of the patient's sample showed the presence of two aberrant transcripts that code for a protein of 519 amino acids. We demonstrate that these two transcripts differ in the 3' UTR region, and result from the use of two alternative polyadenylation signals. The severe phenotype of the patient correlates with the presence of an aberrant protein.

Genotype-Proteotype Linkage in the Wiskott-Aldrich Syndrome

Wiskott-Aldrich syndrome (WAS) is a platelet/immunodeficiency disease arising from mutations of WAS protein (WASP), a hemopoietic cytoskeletal protein. Clinical symptoms vary widely from mild (X-linked thrombocytopenia) to life threatening. In this study, we examined the molecular effects of individual mutations by quantifying WASP in peripheral lymphocytes of 44 patients and identifying the molecular variant (collectively called proteotype). Nonpredicted proteotypes were found for 14 genotypes. These include WASP-negative lymphocytes found for five missense genotypes and WASP-positive lymphocytes for two nonsense, five frameshift, and two splice site genotypes. Missense mutations in the Ena/VASP homology 1 (EVH1) domain lead to decreased/absent WASP but normal mRNA levels, indicating that proteolysis causes the protein deficit. Because several of the EVH1 missense mutations alter WIP binding sites, the findings suggest that abrogation of WIP binding induces proteolysis. Whereas platelets of most patients were previously shown to lack WASP, WASP-positive platelets were found for two atypical patients, both of whom have mutations outside the EVH1 domain. WASP variants with alternative splicing and intact C-terminal domains were characterized for eight nonsense and frameshift genotypes. One of these, a nonsense genotype in a mild patient, supports expression of WASP lacking half of the proline-rich region. With one notable exception, genotype and proteotype were linked, indicating that a genotype-proteotype registry could be assembled to aid in predicting disease course and planning therapy for newly diagnosed infants. Knowledge of the molecular effect of mutations would aid also in identifying disease-modifying genes.

[Molecular pathogenesis of Wiskott-Aldrich syndrome]

The Wiskott-Aldrich syndrome (WAS) is an X-linked primary immunodeficiency caused by mutations in the gene encoding the WAS protein (WASP). WASP is predominantly expressed in hematopoietic cells and regulates the reorganization of the actin cytoskeleton in response to various important cell stimuli including T cell receptor signaling. WASP is localized at the immunological synapses between T cells and antigen presenting cells, NK cells and target cells. Here we focus on recent basic and clinical research advances for WAS, which has given great insight into the relevance of WASP, its related molecules and its interacting proteins to basic cell biology, actin cytoskeleton, immunological defects and prediction of clinical outcome in WAS patients. In particular, we have reported the significance of WIP (WASP-interacting protein) for molecular regulation of WASP. In addition, we discuss recent basic approaches to gene therapy for WAS.

Recurrent V75M mutation within the Wiskott-Aldrich syndrome protein: description of a homozygous female patient

The Wiskott-Aldrich syndrome is a rare genetic disorder due to mutations in the WAS gene situated on chromosome X. It is comprised of microthrombocytopenia, eczema and immunodeficiency. However, the phenotypical presentation may vary as to the number and intensity of its manifestations. A milder form of Wiskott-Aldrich syndrome is known as the X-linked thrombocytopenia. We independently found eight individual or familial cases with the V75M substitution (9.76%). This high incidence was partly accounted for by the fact that three cases turned out to be related. The V75M mutation is recurrent, however, due to a CpG island. A genuine homozygous female patient was found. She showed microthrombocytopenia and infections to the same degree as her hemizygous father and brother. The WAS protein was decreased in a comparable fashion in the hemizygotes and the homozygote as well. Its amount was about 10% and 15% of normal in platelets and mononucleated white cells, respectively. In all patients was the picture consistent with XLT.

Human disease resulting from gene mutations that interfere with appropriate nuclear factor-kappaB activation

The nuclear factor (NF)-kappaB family of transcription factors serves vital roles in a wide array of cell functions. An increasing number of human genetic lesions that result in defined disease entities are linked to inappropriate activation of NF-kappaB. The resulting aberrant NF-kappaB function can lead to cellular defects that ultimately impair normal developmental processes, host immune defenses, or both. Molecular defects that lie upstream in cell-signaling pathways and rely upon NF-kappaB activation tend to give a more specific phenotype, whereas those closer to the actual NF-kappaB proteins have broader defects. A detailed study of these diseases can provide insight into the biochemistry of NF-kappaB activation as well as the role of NF-kappaB in human health.

Lentiviral vectors transcriptionally targeted to hematopoietic cells by WASP gene proximal promoter sequences

The development of vectors that express a therapeutic transgene efficiently and specifically in hematopoietic cells (HCs) is an important goal for gene therapy of hematological disorders. In order to achieve this, we used a 500 bp fragment from the proximal WASP gene promoter to drive the expression of the WASP cDNA in the context of a self-inactivating lentiviral vector. Single-round transduction of WASp-deficient herpesvirus saimiri (HVS)-immortalized cells as well as primary allospecific T cells from Wiskott-Aldrich syndrome (WAS) patients with this vector (WW) resulted in expression levels similar to those of control cells. Non-HCs were transduced with similar efficiency, but the levels of WASp were 135-350 times lower than those achieved in HCs. Additionally, transduction of WASp-deficient cells with WW conferred a selective growth advantage in vitro. Therefore, lentiviral vectors incorporating proximal promoter sequences from the WASP gene confer hematopoietic-specific, and physiological protein expression.

Genetic immunodeficiency disorders

In this review, selected immunodeficiency disorders are presented in which the cutaneous signs are distinctive and contribute to the diagnosis of the condition. Among these cutaneous abnormalities are alopecia, cutaneous granulomas, cutaneous infections, atopic-like or seborrheic-like dermatitis, petechiae or purpura, silvery pigmentation, poor wound healing, and telangiectasias. Immunodeficiency should be considered in children with a history of infections that are recurrent, respond poorly to antibiotics, are of increased duration and severity, and/or result from unusual organisms. In addition to their high risk of infection, patients with immunodeficiency disorders have a risk of the development of malignancy that is 10,000 times higher than that of healthy age-matched controls. The underlying molecular basis for most genetic immunodeficiencies is now understood, allowing improved genetic counseling and prenatal diagnosis.

WASP (Wiskott-Aldrich syndrome protein) gene mutations and phenotype

PURPOSE OF REVIEW

Wiskott-Aldrich syndrome (WAS) and X-linked thrombocytopenia (XLT), characterized by chronic microthrombocytopenia with and without immunodeficiency, are caused by mutations of the WAS protein (WASP) gene. WASP has been reported to interact with many cytoplasmic molecules linking cellular signaling to the actin cytoskeleton. In this review we will focus on recent molecular findings that provide a better understanding of the pathogenesis of this complex disease and explore the correlation of genotype and clinical phenotype.

RECENT FINDINGS

Recent investigations have provided evidence that WASP and several related proteins are involved in the reorganization of the actin cytoskeleton by activating Arp2/3-mediated actin polymerization. This function is controlled mainly by a small GTPase Cdc42. Activated GTP-bound Cdc42 dissociates the intramolecular autoinhibitory loop formation of WASP. In addition, WASP is involved in cytoplasmic signaling by its interaction with a variety of adaptor molecules or kinases and serves as a link to actin reorganization, which is important for immunological synapse formation, cell trafficking and motility. Tyrosine or serine phosphorylation of WASP increases the actin polymerization activity of WASP via Arp2/3. Mutation analysis of WAS/XLT patients has provided evidence for a strong correlation between phenotype and genotype. Gene therapy for WASP-deficient human lymphocytes and Wasp-deficient mice was performed successfully.

SUMMARY

The study of WASP and its mutations has led to a better understanding of the pathogenesis of the syndrome (thrombocytopenia, immunodeficiency, atopic dermatitis, autoimmune and malignant diseases) and the mechanisms required for cell mobility, cell-cell interaction and cytoplasmic signaling, as well as thrombopoiesis and maintenance of the number of platelets.

IgA nephropathy associated with X-linked thrombocytopenia

X-Linked thrombocytopenia (XLT) is characterized by congenital thrombocytopenia with small platelets and absence of immunodeficiency; XLT is an allelic variant of Wiskott-Aldrich syndrome (WAS). Both entities are caused by mutations in the same gene. This study presents the case of an 8-year-old boy with XLT. He developed immunoglobulin A (IgA) nephropathy at the age of 4 years. Genetic analysis confirmed the XLT diagnosis. His maternal uncle also had thrombocytopenia from early infancy and developed end-stage renal failure as a result of IgA nephropathy. The maternal uncle was inferred to be affected with XLT because of the carrier status of the patient's mother. Abnormal glycosylation has a role in pathogenesis in IgA nephropathy; moreover, sialophorin glycosylation is defective in WAS. Altered glycosylation may contribute to renal involvement in patients with WAS/XLT despite different defective glycosylation patterns in IgA nephropathy and WAS/XLT.

Multiple patients with revertant mosaicism in a single Wiskott-Aldrich syndrome family

We previously reported on a 43-year-old patient with Wiskott-Aldrich syndrome (WAS) who experienced progressive clinical improvement and revertant T-cell mosaicism. Deletion of the disease-causing 6-bp insertion was hypothesized to have occurred by DNA polymerase slippage. We now describe 2 additional patients from the same family who also had revertant T lymphocytes that showed selective in vivo advantage. Somatic mosaicism was demonstrated on leukocytes cryopreserved in the first patient when he was 22 years old, 11 years before his death from kidney failure. The second patient is now 16 years old, has a moderate clinical phenotype, and developed revertant cells after the age of 14 years. These results support DNA polymerase slippage as a common underlying mechanism, and they indicate that T-cell mosaicism may have different clinical effects in WAS.

Differential contribution of Wiskott-Aldrich syndrome protein to selective advantage in T- and B-cell lineages

Somatic mosaicism because of in vivo reversion has been recently reported in a small number of patients affected with Wiskott-Aldrich syndrome (WAS). Flow cytometry analysis of WAS protein (WASP) expression has shown that these patients carried revertant cells only among T lymphocytes. Here, we have used high-resolution capillary electrophoresis to analyze genomic DNA from highly purified cells of one of these patients and detected revertant sequences also within the B-cell fraction. The demonstration of revertant cells among both T and B lymphocytes in this patient is consistent with the reversion event having occurred in a common lymphoid progenitor. However, although WASP-expressing T cells showed selective advantage and were readily detectable in the periphery of the mosaic patient, revertant B lymphocytes remained below the detection threshold of flow cytometry. These findings suggest that, contrary to T cells, differentiation and survival of B lymphocytes is minimally dependent on WASP.

Wiskott–Aldrich syndrome in a female with skewed X-chromosome inactivation

Wiskott-Aldrich syndrome (WAS) is an X-linked recessive disorder characterized by immunodeficiency, eczema, and thrombocytopenia with small platelets. The phenotype of affected males is usually severe, although female carriers of the disorder have no clinical signs of the genetic defect. This is explained by the preferential selection of the normal, nonmutated X-chromosome, as the active allele in hematopoietic cells. In the present article we describe a female case of WAS, with a G-to-A transition in the WASP gene at nucleotide 291. She displays mild thrombocytopenia, with both normal and small-sized platelets. A methylation analysis of the HUMARA gene showed a nonrandom X-chromosome inactivation pattern in which the X-chromosome carrying the normal WASP gene was preferentially inactivated, leaving the mutant gene active. Thus, our results suggest that skewed X-inactivation, favoring the WASP-mutated allele, is the mechanism underlying the WAS phenotype of this girl. Moreover the results alert us to the fact that particular females, with a family history of WAS, may develop certain signs of the disease.

Wiskott—Aldrich Syndrome: a model for defective actin reorganization, cell trafficking and synapse formation

Wiskott-Aldrich Syndrome (WAS) is an X-linked immunodeficiency characterized by thrombocytopenia with small platelets, eczema, recurrent infections, autoimmune disorders and increased incidence of malignancies. Classic WAS, and a milder form, X-linked thrombocytopenia, are caused by mutations of the WAS protein (WASP) gene. Recent investigations have provided evidence that WASP and several related proteins are involved in the reorganization of the actin cytoskeleton by activating Arp2/3-mediated actin polymerization. This function is controlled by the small GTPase Cdc42, which regulates the autoinhibitory loop formation of WASP. In addition, WASP is involved in cytoplasmic signaling via its interaction with a variety of adaptor molecules. Mutation analysis of large cohorts of WAS/X-linked thrombocytopenia patients has provided evidence for a strong correlation between phenotype and genotype.