Wiskott-Aldrich syndrome: a study of 577 patients defines the genotype as a biomarker for disease severity and survival.

ABSTRACT: Wiskott-Aldrich syndrome (WAS) is a multifaceted monogenic disorder with a broad disease spectrum and variable disease severity and a variety of treatment options including allogeneic hematopoietic stem cell transplantation (HSCT) and gene therapy (GT). No reliable biomarker exists to predict disease course and outcome for individual patients. A total of 577 patients with a WAS variant from 26 countries and a median follow-up of 8.9 years (range, 0.3-71.1), totaling 6118 patient-years, were included in this international retrospective study. Overall survival (OS) of the cohort (censored at HSCT or GT) was 82% (95% confidence interval, 78-87) at age 15 years and 70% (61-80) at 30 years. The type of variant was predictive of outcome: patients with a missense variant in exons 1 or 2 or with the intronic hot spot variant c.559+5G>A (class I variants) had a 15-year OS of 93% (89-98) and a 30-year OS of 91% (86-97), compared with 71% (62-81) and 48% (34-68) in patients with any other variant (class II; P < .0001). The cumulative incidence rates of disease-related complications such as severe bleeding (P = .007), life-threatening infection (P < .0001), and autoimmunity (P = .004) occurred significantly later in patients with a class I variant. The cumulative incidence of malignancy (P = .6) was not different between classes I and II. It confirms the spectrum of disease severity and quantifies the risk for specific disease-related complications. The class of the variant is a biomarker to predict the outcome for patients with WAS.

Impact of the J Project on progress of primary immunodeficiency care in Ukraine.

The J Project is a Central-Eastern European collaborative program in the field of physician education and clinical research aimed at improving the clinical care and diagnosis of primary immunodeficiency disorders (PIDs). Ukraine was one of the first to participate in the project, which allowed us to join the whole European PID community. Since 2004, the country has been holding annual J Project meetings with the involvement of new regions. The spread of the J Project impact has contributed to significantly improved early PID diagnosis in Ukraine. Progress has been made not only in identifying patients but also in arranging the treatment. The assistance in genetic diagnosis made it possible to detect PIDs, study their features, and improve approaches to the management. This also gave an impetus to the development of regional PID centers and participation in scientific research. Of utmost importance is the cooperation with colleagues from Poland, Hungary, and Belarus, who are active members of the J Project.

A Variety of Alu-Mediated Copy Number Variations Can Underlie IL-12Rß1 Deficiency.

PURPOSE: Inborn errors of IFN-γ immunity underlie Mendelian susceptibility to mycobacterial disease (MSMD). Autosomal recessive complete IL-12Rß1 deficiency is the most frequent genetic etiology of MSMD. Only two of the 84 known mutations are copy number variations (CNVs), identified in two of the 213 IL-12Rß1-deficient patients and two of the 164 kindreds reported. These two CNVs are large deletions found in the heterozygous or homozygous state. We searched for novel families with IL-12Rß1 deficiency due to CNVs. METHODS: We studied six MSMD patients from five unrelated kindreds displaying adverse reactions to BCG vaccination. Three of the patients also presented systemic salmonellosis, two had mucocutaneous candidiasis, and one had disseminated histoplasmosis. We searched for CNVs and other variations by IL12RB1-targeted next-generation sequencing (NGS). RESULTS: We identified six new IL-12Rß1-deficient patients with a complete loss of IL-12Rß1 expression on phytohemagglutinin-activated T cells and/or EBV-transformed B cells. The cells of these patients did not respond to IL-12 and IL-23. Five different CNVs encompassing IL12RB1 (four deletions and one duplication) were identified in these patients by NGS coverage analysis, either in the homozygous state (n = 1) or in trans (n = 4) with a single-nucleotide variation (n = 3) or a small indel (n = 1). Seven of the nine mutations are novel. Interestingly, four of the five CNVs were predicted to be driven by nearby Alu elements, as well as the two previously reported large deletions. The IL12RB1 locus is actually enriched in Alu elements (44.7%), when compared with the rest of the genome (10.5%). CONCLUSION: The IL12RB1 locus is Alu-enriched and therefore prone to rearrangements at various positions. CNVs should be considered in the genetic diagnosis of IL-12Rß1 deficiency.

Mycobacterial disease in patients with chronic granulomatous disease: A retrospective analysis of 71 cases.

BACKGROUND: Chronic granulomatous disease (CGD) is a rare primary immunodeficiency caused by inborn errors of the phagocyte nicotinamide adenine dinucleotide phosphate oxidase complex. From the first year of life onward, most affected patients display multiple, severe, and recurrent infections caused by bacteria and fungi. Mycobacterial infections have also been reported in some patients. OBJECTIVE: Our objective was to assess the effect of mycobacterial disease in patients with CGD. METHODS: We analyzed retrospectively the clinical features of mycobacterial disease in 71 patients with CGD. Tuberculosis and BCG disease were diagnosed on the basis of microbiological, pathological, and/or clinical criteria. RESULTS: Thirty-one (44%) patients had tuberculosis, and 53 (75%) presented with adverse effects of BCG vaccination; 13 (18%) had both tuberculosis and BCG infections. None of these patients displayed clinical disease caused by environmental mycobacteria, Mycobacterium leprae, or Mycobacterium ulcerans. Most patients (76%) also had other pyogenic and fungal infections, but 24% presented solely with mycobacterial disease. Most patients presented a single localized episode of mycobacterial disease (37%), but recurrence (18%), disseminated disease (27%), and even death (18%) were also observed. One common feature in these patients was an early age at presentation for BCG disease. Mycobacterial disease was the first clinical manifestation of CGD in 60% of these patients. CONCLUSION: Mycobacterial disease is relatively common in patients with CGD living in countries in which tuberculosis is endemic, BCG vaccine is mandatory, or both. Adverse reactions to BCG and severe forms of tuberculosis should lead to a suspicion of CGD. BCG vaccine is contraindicated in patients with CGD.

Molecular Characteristics, Clinical and Immunologic Manifestations of 11 Children with Omenn Syndrome in East Slavs (Russia, Belarus, Ukraine).

BACKGROUND: Omenn syndrome [Mendelian Inheritance (OMIM 603554)] is a genetic disease of the immune system, characterized by the presence of fatal generalized severe erythroderma, lymphoadenopathy, eosinophilia and profound immunodeficiency. OBJECTIVE: We studied clinical and immunologic presentation of the disease manifestation among East Slavs population with genetically confirmed Omenn syndrome. RESULTS: We collected clinical and immunologic data of 11 patients (1 from Belarus, 5--Ukraine, 5--Russia): 6 females, 5 males. The age of Omenn syndrome manifestation varied from the 1st day of life to 1 year and 1 month, the age of diagnosis--20 days to 1 year and 10 months. Nine out of 11 patients had classic immunologic phenotype T(+/-)B-NK+, 1 pt had TlowB + NK+ with CD3 + TCRgd + expansion and 1 had TlowB+/-NK+ phenotype. Eight out of 11 pts had mutation in RAG1 gene, 4 out of 8 had c.368-369delAA (p.K86fsX118) in homozygous state or heterozygous compound. In our cohort of patients, we also described two new mutations in RAG genes (p.E722Q in RAG1 and p.M459R in RAG2). At present, 7/11 were transplanted and 5 out of the transplanted are alive. CONCLUSION: This study demonstrates that the most popular genetic abnormality in East Slavs children with Omenn syndrome is c.368-369delAA (p.K86fs118) in RAG1 gene, which may be connected with more favorable prognosis because 4/4 patients survived after hematopoietic stem cells transplantation.

New and recurrent gain-of-function STAT1 mutations in patients with chronic mucocutaneous candidiasis from Eastern and Central Europe.

BACKGROUND: Chronic mucocutaneous candidiasis disease (CMCD) may result from various inborn errors of interleukin (IL)-17-mediated immunity. Twelve of the 13 causal mutations described to date affect the coiled-coil domain (CCD) of STAT1. Several mutations, including R274W in particular, are recurrent, but the underlying mechanism is unclear. OBJECTIVE: To investigate and describe nine patients with CMCD in Eastern and Central Europe, to assess the biochemical impact of STAT1 mutations, to determine cytokines in supernatants of Candida-exposed blood cells, to determine IL-17-producing T cell subsets and to determine STAT1 haplotypes in a family with the c.820C>T (R274W) mutation. RESULTS: The novel c.537C>A (N179K) STAT1 mutation was gain-of-function (GOF) for γ-activated factor (GAF)-dependent cellular responses. In a Russian patient, the cause of CMCD was the newly identified c.854 A>G (Q285R) STAT1 mutation, which was also GOF for GAF-dependent responses. The c.1154C>T (T385M) mutation affecting the DNA-binding domain (DBD) resulted in a gain of STAT1 phosphorylation in a Ukrainian patient. Impaired Candida-induced IL-17A and IL-22 secretion by leucocytes and lower levels of intracellular IL-17 and IL-22 production by T cells were found in several patients. Haplotype studies indicated that the c.820C>T (R274W) mutation was recurrent due to a hotspot rather than a founder effect. Severe clinical phenotypes, including intracranial aneurysm, are presented. CONCLUSIONS: The c.537C>A and c.854A>G mutations affecting the CCD and the c.1154C>T mutation affecting the DBD of STAT1 are GOF. The c.820C>T mutation of STAT1 in patients with CMCD is recurrent due to a hotspot. Patients carrying GOF mutations of STAT1 may develop multiple intracranial aneurysms by hitherto unknown mechanisms.

Nijmegen breakage syndrome: 25-year experience of diagnosis and treatment in Ukraine.

Introduction: Nijmegen breakage syndrome (NBS) is an autosomal recessive disorder, characterized by microcephaly, immunodeficiency, and impaired DNA repair. NBS is most prevalent among Slavic populations, including Ukraine. Our study aimed to comprehensively assess the prevalence, diagnosis, clinical data, immunological parameters, and treatment of NBS patients in Ukraine. Methods: We conducted a retrospective review that included 84 NBS patients from different regions of Ukraine who were diagnosed in 1999-2023. Data from the Ukrainian Registry of NBS and information from treating physicians, obtained using a developed questionnaire, were utilized for analysis. Results: Among 84 NBS patients, 55 (65.5%) were alive, 25 (29.8%) deceased, and 4 were lost to follow-up. The median age of patients was 11 years, ranging from 1 to 34 years. Most patients originate from western regions of Ukraine (57.8%), although in recent years, there has been an increase in diagnoses from central and southeastern regions, expanding our knowledge of NBS prevalence. The number of diagnosed patients per year averaged 3.4 and increased from 2.7 to 4.8 in recent years. The median age of NBS diagnosis was 4.0 years (range 0.1-16) in 1999-2007 and decreased to 2.7 in the past 6 years. Delayed physical development was observed in the majority of children up to the age of ten years. All children experienced infections, and 41.3% of them had recurrent infections. Severe infections were the cause of death in 12%. The second most common clinical manifestation of NBS was malignancies (37.5%), with the prevalence of lymphomas (63.3%). Malignancies have been the most common cause of death in NBS patients (72% of cases). Decreased levels of CD4+ and CD19+ were observed in 89.6%, followed by a reduction of CD3+ (81.8%) and CD8+ (62.5%). The level of NK cells was elevated at 62.5%. IgG concentration was decreased in 72.9%, and IgA - in 56.3%. Immunoglobulin replacement therapy was administered to 58.7% of patients. Regular immunoglobulin replacement therapy has helped reduce the frequency and severity of severe respiratory tract infections. Conclusion: Improvements in diagnosis, including prenatal screening, newborn screening, monitoring, and expanding treatment options, will lead to better outcomes for NBS patients.

Evaluation of the effectiveness of Haemophilus influenzae type b conjugate vaccine introduction against radiologically-confirmed hospitalized pneumonia in young children in Ukraine.

OBJECTIVE: Haemophilus influenzae type b (Hib) conjugate vaccine was included into the national vaccination schedule of Ukraine in 2006. The objective of this study was to demonstrate the effectiveness of Hib conjugate vaccine against radiologically-confirmed hospitalized pneumonia in children. STUDY DESIGN: Children <2 years old with radiologically confirmed pneumonia admitted to 11 participating hospitals in Kiev and Dnepropetrovsk between April 2007 and June 2009 were included in a case-control evaluation. Four controls were matched to each case by date of birth (within 14 days) and outpatient clinic. We estimated ORs for vaccination and vaccine effectiveness ((1 - OR)*100%) using conditional logistic regression, adjusting for comorbid conditions and contraindications for vaccination. RESULTS: We enrolled 188 case-children and 735 controls. Median age was 16 months (range 4-24 months). Fifty-one percent of cases and 67% of controls received ≥1 doses of Hib conjugate vaccine; 26% of cases and 37% of controls received ≥3 doses. The effectiveness of ≥1 dose Hib conjugate vaccine was estimated at 45% (95% CI 18%-63%). CONCLUSIONS: Our study showed that Hib infections are important causes of hospitalized radiologically confirmed pneumonia in young children in Ukraine.

Molecular mechanisms of mucocutaneous immunity against Candida and Staphylococcus species.

Signal transducer and activator of transcription (STAT) proteins are key components of the innate and adaptive immune responses to pathogenic microorganisms. Recent research on primary immunodeficiency disorders and the identification of patients carrying germline mutations in STAT1, STAT3, and STAT5B have highlighted the role of human STATs in host defense against various viruses, bacteria, and fungi. Mutations in STAT1 and STAT3 disrupt various cytokine pathways that control mucocutaneous immunity against Candida species, especially Candida albicans, and Staphylococcus species, especially Staphylococcus aureus. Here we consider inborn errors of immunity arising from mutations in either STAT1 or STAT3 that affect mucocutaneous immunity to Candida and Staphylococcus species.

Variable CD18 expression in a 22-year-old female with leukocyte adhesion deficiency I: Clinical case and literature review.

Key Clinical Message: Partial leukocyte adhesion deficiency type 1 (LAD-1) deficiency is extremely rare condition with milder infectious manifestation and immune system imbalance leads to increased risks of autoinflammatory complications, such as pyoderma gangrenosum, that can be triggered by trauma or pregnancy. In patients with spice-site ITGB2 variants, partial expression can occur due to different ß2 integrin isophorms expression. Abstract: LAD-1, OMIM ID #116920 is a rare, autosomal recessive disorder that results from mutations in the ITGB2 gene that encodes the CD18 ß2 integrin subunit. According to the CD18 expression, LAD-1 is categorized as severe (<2%), moderate (2%-30%), or mild (>30%). Here, we describe a 22-year-old female, who presented with inflammatory skin disease and oral cavity, as well as respiratory tract infections during the first year of life. LAD-1 was diagnosed at the age of 2 years by low expression of CD18 (1%). Whole-exome sequencing identified homozygous c. 59-10C>A variant in the ITGB2 gene. Despite severe phenotype, the patient survived to adulthood without hematopoietic stem cell transplantation and became pregnant at the age of 20 years, with pregnancy complicated by a pyoderma gangrenosum-like lesion. During her life, CD18 expression increased from 1% to 9%; at 22 years of age, 5% of neutrophils and 9% of lymphocytes were CD18+. All CD18+-lymphocytes were predominantly memory/effector cytotoxic T cells. However, revertant mosaicism was not being established suggesting that CD18 expression variability may be mediated by other mechanisms such as different ß2 integrin isophorms expression.

The Clinical and Genetic Spectrum of 82 Patients With RAG Deficiency Including a c.256_257delAA Founder Variant in Slavic Countries.

Background: Variants in recombination-activating genes (RAG) are common genetic causes of autosomal recessive forms of combined immunodeficiencies (CID) ranging from severe combined immunodeficiency (SCID), Omenn syndrome (OS), leaky SCID, and CID with granulomas and/or autoimmunity (CID-G/AI), and even milder presentation with antibody deficiency. Objective: We aim to estimate the incidence, clinical presentation, genetic variability, and treatment outcome with geographic distribution of patients with the RAG defects in populations inhabiting South, West, and East Slavic countries. Methods: Demographic, clinical, and laboratory data were collected from RAG-deficient patients of Slavic origin via chart review, retrospectively. Recombinase activity was determined in vitro by flow cytometry-based assay. Results: Based on the clinical and immunologic phenotype, our cohort of 82 patients from 68 families represented a wide spectrum of RAG deficiencies, including SCID (n = 20), OS (n = 37), and LS/CID (n = 25) phenotypes. Sixty-seven (81.7%) patients carried RAG1 and 15 patients (18.3%) carried RAG2 biallelic variants. We estimate that the minimal annual incidence of RAG deficiency in Slavic countries varies between 1 in 180,000 and 1 in 300,000 live births, and it may vary secondary to health care disparities in these regions. In our cohort, 70% (n = 47) of patients with RAG1 variants carried p.K86Vfs*33 (c.256_257delAA) allele, either in homozygous (n = 18, 27%) or in compound heterozygous (n = 29, 43%) form. The majority (77%) of patients with homozygous RAG1 p.K86Vfs*33 variant originated from Vistula watershed area in Central and Eastern Poland, and compound heterozygote cases were distributed among all Slavic countries except Bulgaria. Clinical and immunological presentation of homozygous RAG1 p.K86Vfs*33 cases was highly diverse (SCID, OS, and AS/CID) suggestive of strong influence of additional genetic and/or epigenetic factors in shaping the final phenotype. Conclusion: We propose that RAG1 p.K86Vfs*33 is a founder variant originating from the Vistula watershed region in Poland, which may explain a high proportion of homozygous cases from Central and Eastern Poland and the presence of the variant in all Slavs. Our studies in this cohort of RAG1 founder variants confirm that clinical and immunological phenotypes only partially depend on the underlying genetic defect. As access to HSCT is improving among RAG-deficient patients in Eastern Europe, we anticipate improvements in survival.

Observations on the epidemiology of rotavirus infection among hospitalized children younger than 5 years in 2 Ukrainian hospitals, 2007-2015.

BACKGROUND: Acute gastroenteritis remains a burden among children under 5 years of age. Ukraine joined the World Health Organization's Global Rotavirus Surveillance Network in 2006, with a goal of providing accurate rotavirus burden data to aid policy makers in planning for rotavirus vaccine introduction. This analysis describes rotavirus epidemiology among Ukrainian children enrolled in Kyiv and Odesa, two large Ukrainian cities. METHODS: Children 0-59 months of age hospitalized for acute gastroenteritis at 2 sentinel sites in Kyiv and Odesa were enrolled into the active, prospective surveillance program. In Odesa, the surveillance period was during 2007-2015 and in Kyiv, it was during 2011-2015. Acute gastroenteritis was defined as 3 or more episodes of diarrhea per day during a 24 h period, with symptom duration before hospitalization not exceeding 7 days. Guardians of enrolled children completed a questionnaire including demographic, clinical and treatment information. Each child provided a stool specimen within 2 days of hospitalization. Stools were tested for rotavirus using ProSpecT™ Rotavirus Kit (Oxoid Ltd., Great Britain), and positive specimens were genotyped. Descriptive data are reported, as well as comparison of demographic, clinical and treatment data among rotavirus positive and negative children. RESULTS: During July 2007-June 2015, 12,350 children were enrolled in the surveillance programs and had stool specimens collected and tested for rotavirus. Overall, rotavirus infection was diagnosed in 5412/12350 (44%) of children, 929/1734 (54%) of those in Kyiv and 4483/10616 (42%) in Odesa. Rotavirus infections peaked during the winter months. Children with rotavirus acute gastroenteritis displayed more severe clinical symptoms than those without rotavirus. Predominant genotypes identified included G1P[8], G2P[4], G3 P[8], G4 P[8] and G9 P[8]. CONCLUSION: Active surveillance of acute gastroenteritis in hospitalized children younger 5 years in two large Ukrainian cities reveals a significant burden of rotavirus infection. These data provide scientific justification for incorporating rotavirus vaccines into the Ukrainian national immunization schedule.

Surveillance of pneumococcal diseases in Central and Eastern Europe.

Pneumococcal infection is a major cause of morbidity and mortality worldwide. The burden of disease associated with S. pneumoniae is largely preventable through routine vaccination. Pneumococcal conjugate vaccines (e.g. PCV7, PCV13) provide protection from invasive pneumococcal disease as well as non-invasive infection (pneumonia, acute otitis media), and decrease vaccine-type nasopharyngeal colonisation, thus reducing transmission to unvaccinated individuals. PCVs have also been shown to reduce the incidence of antibiotic-resistant pneumococcal disease. Surveillance for pneumococcal disease is important to understand local epidemiology, serotype distribution and antibiotic resistance rates. Surveillance systems also help to inform policy development, including vaccine recommendations, and monitor the impact of pneumococcal vaccination. National pneumococcal surveillance systems exist in a number of countries in Central and Eastern Europe (such as Croatia, Czech Republic, Hungary, Poland, Romania and Slovakia), and some have introduced PCVs (Czech Republic, Hungary, Kazakhstan, Russia, Slovakia and Turkey). Those countries without established programs (such as Kazakhstan, Russia and Ukraine) may be able to learn from the experiences of those with national surveillance systems. The serotype distributions and impact of PCV13 on pediatric pneumococcal diseases are relatively similar in different parts of the world, suggesting that approaches to vaccination used elsewhere are also likely to be effective in Central and Eastern Europe. This article briefly reviews the epidemiology of pneumococcal disease, presents the latest surveillance data from Central and Eastern Europe, and discusses any similarities and differences in these data as well the potential implications for vaccination policies in the region.

Viral gastroenteritis in rotavirus negative hospitalized children <5 years of age from the independent states of the former Soviet Union.

PURPOSE: Rotavirus causes nearly 40% of all hospitalizations for AGE among children <5 years of age in the NIS of the former Soviet Union. The etiologic role of other established gastroenteritis viruses in this age group is unknown. METHODS: Laboratory-confirmed rotavirus negative fecal specimens (N=495) collected between January and December 2009 from children in 6 NIS (Armenia, Azerbaijan, Belarus, Georgia, Republic of Moldova and Ukraine) were tested for norovirus, sapovirus, enteric adenovirus and astrovirus by real-time RT-PCR. Genotyping was carried out by sequencing and phylogenetic analysis. RESULTS: Norovirus, enteric adenovirus, sapovirus and astrovirus were detected in 21.8%, 4.0%, 3.2%, and 1.4% of the rotavirus negative specimens, respectively. Mixed infections were identified in 4.1% of the specimens. Phylogenetic analysis showed co-circulation of several different genotypes with GII.4 Den Haag (2006b) norovirus, GI.2 sapovirus, adenovirus type 41, and astrovirus type 1 causing majority of the infections. CONCLUSION: Norovirus, enteric adenovirus, sapovirus and astrovirus account for a significant proportion (30.5%) of AGE in hospitalized children <5 years of age in 6 NIS.

Genetic characteristics of eighty-seven patients with the Wiskott-Aldrich syndrome.

The Wiskott-Aldrich syndrome (WAS) is an X-linked recessive immune deficiency disorder characterized by thrombocytopenia, small platelet size, eczema, recurrent infections, and increased risk of autoimmune disorders and malignancies. WAS is caused by mutations in the WASP gene which encodes WASP, a 502-amino acid protein. WASP plays a critical role in actin cytoskeleton organization and signalling, and functions of immune cells. We present here the results of genetic analysis of patients with WAS from eleven Eastern and Central European (ECE) countries and Turkey. Clinical and haematological information of 87 affected males and 48 carrier females from 77 WAS families were collected. The WASP gene was sequenced from genomic DNA of patients with WAS, as well as their family members to identify carriers. In this large cohort, we identified 62 unique mutations including 17 novel sequence variants. The mutations were scattered throughout the WASP gene and included single base pair changes (17 missense and 11 nonsense mutations), 7 small insertions, 18 deletions, and 9 splice site defects. Genetic counselling and prenatal diagnosis were applied in four affected families. This study was part of the J Project aimed at identifying genetic basis of primary immunodeficiency disease in ECE countries. This report provides the first comprehensive overview of the molecular genetic and demographic features of WAS in ECE.

Genetic and demographic features of X-linked agammaglobulinemia in Eastern and Central Europe: a cohort study.

Primary immunodeficiency disorders are a recognized public health problem worldwide. The prototype of these conditions is X-linked agammaglobulinemia (XLA) or Bruton's disease. XLA is caused by mutations in Bruton's tyrosine kinase gene (BTK), preventing B cell development and resulting in the almost total absence of serum immunoglobulins. The genetic profile and prevalence of XLA have not previously been studied in Eastern and Central European (ECE) countries. We studied the genetic and demographic features of XLA in Belarus, Croatia Hungary, Poland, Republic of Macedonia, Romania, Russia, Serbia, Slovenia, and Ukraine. We collected clinical, immunological, and genetic information for 122 patients from 109 families. The BTK gene was sequenced from the genomic DNA of patients with a high susceptibility to infection, almost no CD19(+) peripheral blood B cells, and low or undetectable levels of serum immunoglobulins M, G, and A, compatible with a clinical and immunological diagnosis of XLA. BTK sequence analysis revealed 98 different mutations, 46 of which are reported for the first time here. The mutations included single nucleotide changes in the coding exons (35 missense and 17 nonsense), 23 splicing defects, 13 small deletions, 7 large deletions, and 3 insertions. The mutations were scattered throughout the BTK gene and most frequently concerned the SH1 domain; no missense mutation was detected in the SH3 domain. The prevalence of XLA in ECE countries (total population 145,530,870) was found to be 1 per 1,399,000 individuals. This report provides the first comprehensive overview of the molecular genetic and demographic features of XLA in Eastern and Central Europe.