Mutations In Bruton Tyrosine Kinase Gene Research Articles

Trial in Progress: A Phase 1b Study of AS-1763, an Oral, Potent and Selective Noncovalent BTK Inhibitor, in Patients with Previously Treated Chronic Lymphocytic Leukemia/Small Lymphocytic Lymphoma or Non-Hodgkin Lymphoma

Background: Covalent Bruton's tyrosine kinase (BTK) inhibitors such as ibrutinib are approved for treating patients with B-cell malignancies, but their long-term efficacy is limited by toxicity related to off-target kinase inhibition and acquired resistance due to BTK C481 mutation. AS-1763 is a potent, highly selective, orally available, and non-covalent BTK inhibitor, equipotent against both wild-type and C481S-mutated BTK with sub-nanomolar IC50 values (Kawahata et al. J Med Chem 2021; 64,14129-14141). In a Phase 1 single-ascending dose study in healthy volunteers, AS-1763 was well tolerated and safe at doses of 5-600 mg and achieved maximum inhibition of B cell activation at doses of 100 mg and above at 1-2 h post-dose and the duration of inhibitory effect increased with dose [Arimura et al. AACR 2022; Cancer Res 2022;82(12_Suppl)]. In preclinical studies, AS-1763 demonstrated a broad spectrum of inhibition against BTK mutations that confer resistance to other non-covalent BTK inhibitors in addition to the C481 mutation. Study Design and Methods: This study is an open-label, multi-center, Phase 1b study of oral AS-1763 in patients with advanced chronic lymphocytic leukemia (CLL)/small lymphocytic leukemia (SLL) and other B-cell non-Hodgkin lymphomas (NHLs) who have failed or are intolerant to at least two prior lines of systemic therapy. Prior therapy with a covalent BTK inhibitor is permitted; prior use of a noncovalent BTK inhibitor is excluded. This study consists of two parts, i.e., dose escalation and expansion parts. The dose escalation part will follow a 3+3 design with a starting dose of 100 mg BID. Each cycle will be 28 days. Three dose levels will be selected for dose expansion part based on a comprehensive review of data from dose escalation. The dose expansion part consists of 2 cohorts, i.e., Cohort 1 for CLL/SLL and Cohort 2 for B-cell NHL. In each cohort, the first 30 patients will be allocated to the 3 dose levels (10 patients for each), then the same provisional recommended Phase 2 Dose (RP2D) will be selected for Cohort 1 and Cohort 2 after 30 patients have enrolled in either cohort. After the provisional RP2D is selected, up to 28 patients in Cohort 1 and up to 15 patients in Cohort 2 may be treated at the provisional RP2D. In this study, up to 110 patients will be enrolled. Treatment will continue for 24 cycles or until disease progression, occurrence of unacceptable toxicity or discontinuation because of other reasons. Eligible patients include CLL/SLL, Waldenstrӧm macroglobulinemia (WM), marginal zone lymphoma (MZL), mantle cell lymphoma (MCL), and follicular lymphoma (FL). Patients with transformed disease (e.g., Richter's transformation) prior to or during screening are not eligible. Key exclusion criteria include CNS involvement by systemic lymphoma, stem cell transplant or CAR-T therapy <30 days, and clinically significant cardiovascular disease. The primary objective of the dose escalation part is to determine the maximum tolerated dose/dose-limiting toxicity. Key secondary endpoints include the evaluation of safety profile and tolerability, pharmacokinetics properties, and preliminary anti-tumor activity based on overall response rate (ORR) by investigator according to iwCLL 2018 for CLL, IWW6 for WM, and Lugano Treatment Response Criteria for MCL, MZL, SLL and FL. The primary objective of the dose expansion part is to assess the preliminary anti-tumor activity based on ORR by the Safety Monitoring Committee (SMC). Key secondary objectives are to investigate safety, tolerability, and pharmacokinetic profiles and to assess the preliminary antitumor activity based on ORR by investigator and best overall response, duration of response, progression-free survival and overall survival by investigator and the SMC. This trial will evaluate several key exploratory objectives including evaluation of minimal residual disease negativity, characterization of patient subsets defined by mutation status of BTK and phospholipase C gamma 2 (PLCG2), and characterize BTK and PLGC2 gene mutation before and after disease progression. Changes in the level of biomarkers such as CCL3 and CCL4 chemokines and B-cell receptor pathway signaling will be evaluated prior to, during therapy, and at time of disease progression. The RP2D will be determined based on all the data generated in the study. The study has been registered on ClinicalTrials.gov (NCT05602363).

Decreased or Absent B Cells in patients with Severe Reduction in All Serum Immunoglobulin Isotypes, a registry based study

BackgroundSevere Reduction in All Serum Immunoglobulin Isotypes with Profoundly Decreased or Absent B Cells is a subgroup of inborn error of immunities (IEI). 80 to 90% carry mutations in X-chromosomal Bruton tyrosine kinase (BTK) and around 5–10% of the cases are autosomal recessive Agammaglobulinemia (ARA). Very few of Hypogammaglobulinemia with no B cells classified in other subgroups. All of these patients benefit from a genetic evaluation, especially in highly consanguine populations. Materials and Methods27 patients from 11 families with hypogamma-globinemia and no B-cells registered in Immunodeficiency Diseases Research Center registry, Isfahan University of Medical Sciences were phenotypically and genetically evaluated. ResultsThe most prevalent genetic cause was mutations in BTK. The novel mutations in BTK gene includes c.176 G>A (p. Glu89Lys); c.115T>C (p. Tyr39His); c.685-686insTTAC (p. Asn229llefs5), in ARA includes a homozygous stop mutation in Immunoglobulin Heavy Constant Mu Chain (IGHM) gene, a frameshift mutation of B-Cell Antigen Receptor Complex-Associated Protein (CD79A), a bi-allelic stop-gain mutation in Transcription Factor 3 (TCF3), and in PIK3CD also in others IEI includes :novel homozygous silent mutations in Phosphoinositide-3-Kinase Regulatory Subunit (RASGRP1), homozygote SAMD9 mutation. DiscussionWe did not observe any phenotypically significant differences in XLA patients.The main clinical manifestation of ARA cases is, recurrent infections. However, patient with IGHM deficiency had earlier onset of the disease and more severe complications. In CD79A deficient case with 5 affected members and four deaths in her family, the symptoms started very early but managed properly according to the family history. Due to the late diagnosis of PIK3CD cases, more severe complications like bronchiectasis, neurologic sequels after poliomyelitis, and SLE nephropathy has been developed. Our novel SAMD9 had quite different phenotype and the novel RASPGR2 case with no B cells unfortunately managed as ARA before genetic diagnosis and has died of lymphoma as her 3 siblings. However, we observed that in families with more than one affected family member, the disease was better controlled in the second patient. ConclusionOur study broadens the genetic spectrum of hypogammaglobulinemia with no B cells in Iran. This helps differentiate phenotypes and genotypes and manage patients appropriately.

Abstract CT128: Phase 1 study of HSK29116, a Bruton tyrosine kinase (BTK) proteolysis-targeting chimera (PROTAC) agent, in patients with relapsed or refractory B-cell malignancies

Abstract BACKGROUND: BTK, a non-receptor kinase in the B-cell receptor signaling pathway, plays an essential role in B-cell development and differentiation. BTK is critical for malignant B-cell survival. Oral BTK inhibitors (BTKis), standard treatments for patients (pts) with B-cell malignancies, prevent proliferation and induce apoptosis of B cells. Currently approved BTKis covalently bind to BTK residue C481, irreversibly inhibiting phosphorylation of downstream kinases and blocking B-cell activation. Because these agents are often given continuously, their use may lead to clinical resistance and unacceptable toxicities. Indeed, acquired resistance to covalent BTKis is common and caused by the expansion of clones with a cysteine-to-serine mutation at residue 481. A novel strategy being developed to overcome BTKi resistance, is PROTAC-induced degradation of BTK. PROTACs are small molecules with one domain that binds the target protein linked to another domain that binds to ubiquitin E3 ligase, resulting in ubiquitin-dependent proteasome degradation of the target protein. HSK29116 is a small BTK PROTAC molecule that is currently undergoing clinical investigation for the treatment of B-cell malignancies. In preclinical studies, HSK29116 overcame drug resistance caused by the C481S BTK mutation. Also, HSK29116 has demonstrated inhibition of B-cell proliferation without measurable loss of other BTK-family kinase activities. This kinase selectivity may limit some of the off-target toxicities seen with currently available BTKis. METHODS: This first-in-human, multicenter, open-label, phase 1 study (NCT04861779) began recruiting in 2021 to evaluate the safety, tolerability, pharmacokinetics (PK), and pharmacodynamics of oral HSK29116. Eligible pts are ≥18 years old with diagnosis of a B-cell malignancy that has relapsed or become refractory to standard therapy (≥2 prior systemic therapies, which may have included a BTKi) and for which no other treatments known to provide clinical benefit exist. Pts must have an Eastern Cooperative Oncology Group performance status ≤2 and life expectancy >3 months. Phase 1a includes dose escalation to identify dose-limiting toxicities and establish the maximum tolerated dose and/or recommended dose of HSK29116 for a phase 1b dose expansion, initiating in the US. Approximately 36 pts will be enrolled in phase 1a and 90 pts in phase 1b (≥40 pts must have previously received covalent BTKis). The primary endpoint is safety. Secondary endpoints include PK and investigator-assessed overall response rate, duration of response, time to response, and progression-free survival. Exploratory analyses will evaluate the relationship between HSK29116 anti-tumor activity and BTK gene mutations, as well as BTK protein degradation effects of HSK29116. Descriptive statistics will be used to summarize all data. Citation Format: Jianyong Li, Wei Xu, Pangke Yan, Yong Cao, Mengyue Hu, William Daley. Phase 1 study of HSK29116, a Bruton tyrosine kinase (BTK) proteolysis-targeting chimera (PROTAC) agent, in patients with relapsed or refractory B-cell malignancies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT128.

X-Linked Agammaglobulinemia With Chronic Meningoencephalitis: A Diagnostic Challenge

X-linked agammaglobulinemia (XLA) is a primary disorder of humoral immunity characterized by Bruton tyrosine kinase gene mutations resulting in a primary antibody deficiency. While an intact T-cell function largely protects against majority of viral infections, enteroviruses are notorious for infecting these patients due to impaired mucosal immunity. Although the incidence of enteroviral meningoencephalitis in XLA is only 1-5%, yet the mortality is quite high. A typical presentation of enteroviral encephalitis in XLA is a subacute to chronic nervous system infection. A progressive loss of motor and cognitive milestones, spastic quadriplegia, coma, and death are common presentations. The histopathological features reflect gliosis, gradual neuronal loss, neuronophagia, and microglial proliferation. We describe the clinical and brain histopathological findings in a 2-year-old boy with XLA and progressive encephalitis, possibly due to an enteroviral infection.

A Novel BTK Gene Mutation in a Child With Atypical X-Linked Agammaglobulinemia and Recurrent Hemophagocytosis: A Case Report

X-linked agammaglobulinemia (XLA), caused by a mutation in the Bruton's tyrosine kinase (BTK) gene, is rarely reported in patients with recurrent hemophagocytic lymphohistiocytosis (HLH). This mutation leads to significantly reduced numbers of circulatory B cells and serum immunoglobulins in patients. Therefore, they exhibit repetitive bacterial infections since infancy, and immunoglobulin (Ig) replacement therapy is the primary treatment. HLH is a life-threatening condition with manifestations of non-remitting fever, hepatosplenomegaly, cytopenias, coagulopathy, lipid disorder, and multiple organ failure. It is caused by the immune dysregulation between cytotoxic T cells, NK cells, and histiocytes. The treatment is based on HLH-2004 protocol including immunotherapy, chemotherapy, supportive therapy, and stem cell transplantation. However, as we know more about the classification and pathophysiology of HLH, the treatment is modified. T-cell-directed immunotherapy is effective in patients with primary HLH, and strong immunosuppression is contraindicated in patients with severe ongoing infections or some primary immunodeficiency diseases (PIDs). Here, we report the case of a 7-year-old boy who presented with ecthyma gangrenosum and several episodes of pyogenic infections during childhood. At the age of 5 years, he exhibited cyclic HLH every 2–3 months. The remission of HLH episodes finally achieved after he received monthly Ig replacement therapy (400 mg/kg) at the 4th HLH. However, transient elevation of IgM was incidentally discovered after 6 cycles of monthly Ig replacement therapy. IgM-secreting multiple myeloma, Waldenström's macroglobulinemia, and lymphoma were excluded. The IgM levels then declined and returned to the normal range within a year. The patient and his parents received whole-genome sequencing analysis. It revealed a novel hemizygous c.1632-1G>A mutation in the BTK gene and XLA was diagnosed. XLA exhibits a spectrum of clinical and immunological presentations in patients. The identification of the mutation in the BTK gene contribute to an accurate diagnosis. Ig replacement therapy is the primary treatment for HLH in patients with XLA.

Treatment for X-Linked Agammaglobulinemia with Allogeneic Umbilical Cord Blood Stem Cell Transplantation from HLA-Matched Sibling Confirmed Healthy through Prenatal Diagnosis

Background X-linked agammaglobulinemia (XLA) is a rare congenital humoral immunodeficiency characterized by marked reduction in all classes of serum immunoglobulins and the near absence of mature CD19+ B-cells which was caused by mutations in Bruton's tyrosine kinase (BTK). We herein describe the first case of XLA transplanted from HLA-matched sibling allogeneic umbilical cord blood donor.Method The patient was an 8-year-old boy with XLA who previously had life-threatening infectious episodes and diagnosed by direct sequencing of BTK gene mutations (c.992-923delGAN(NM-000061)) when he was 3 years old. He was treated with the regular replacement of immunoglobulin G (IgG) products. Taking into consideration significant infectious complications and the prompt availability of HLA-matched sibling umbilical cord blood, he underwent HLA-matched sibling UCBT. The FC conditioning regimen consisting of Flu (30mg/m2/d×4 days) and CTX (30mg/kg/d×4 days) was provided for the patient. The source of stem cells was umbilical cord blood of his younger brother who was confirmed completely healthy through prenatal diagnosis with villi at the fetus period of 4 months. The number of infused total nucleated and CD34+ cells was 6.51×108/L and 2.67×106/L, respectively. He received a combination of CsA, short-term MTX and MMF for GVHD prophylaxis.Result Hematopoietic engraftment was rapidly achieved, with an absolute neutrophil count of >0.5×109/L on day 15 and platelet count of >20×109/L on day 20. The patient was discharged on day 45 and has been followed as an outpatient without any infectious episodes for more than 180 days. No expected toxicities were observed. Regarding immune constitution, CD19+ cells, IgA and IgM, which were undetectable before transplantation, started to increase in number 10 days after transplantation and continued to increase for more than 3 months. The patient did not exhibit any GVHD manifestations. He is currently alive and doing well at six months post-transplant, and he is free of any infection episodes.Conclusion The above results provide strong evidence that HLA-matched sibling UCBT may be safe and technically feasible for the treatment of XLA when an appropriately matched related or unrelated donor is unavailable. The umbilical cord blood could be considered being frozen, especially in the era of “the second child” in China.Keywords X-linked agammaglobulinemia; HLA-matched sibling donor; allogeneic umbilical cord blood stem cell transplantation; immune recovery. DisclosuresNo relevant conflicts of interest to declare.

Molecular characterization and function analysis of grouper (Epinephelus coioides) Bruton's tyrosine kinase BTK

Bruton's tyrosine kinase (BTK) is a Tec-family tyrosine kinase and plays a crucial role in B cell antigen receptor (BCR) signal pathway. Mutations in humans and mice BTK gene results in X-linked agammaglobulinemia (XLA) and X-linked immunodeficiency (XLD), respectively. To study the function of BTK in teleost, we cloned a BTK gene from orange-spotted grouper. Homology analysis showed that the grouper BTK (EcBTK) had a high amino acid identity with other vertebrates (63%–92%) and shared the highest amino acid identity with ballan wrasse Labrus bergylta BTK. EcBTK comprises a Bruton's tyrosine kinase pleckstrin homology (PH) domain, a Tec homology (TH) domain, a Src homology 3 (SH3) domain, a Src homology 2 (SH2) domain and a Protein Kinases, catalytic (PKc) domain. Tissue distribution analysis showed that EcBTK was mainly expressed in immune organs. EcBTK was uniform distributed throughout the cytoplasm of transfected HEK293T cells and overexpression of EcBTK slightly down-regulates NF-κB activity. Ibrutinib treatment can reduce the phosphorylation level of grouper's BTK. In groupers infected with Cryptocaryon irritans, up-regulation of EcBTK were not seen in the early stage of infected skin and gill until days 14–21. The phosphorylation level of grouper BTK was significantly increased in infected skin and gill.

X-linked agammaglobulinemia in children

X-linked agammaglobulinemia (XLA) is one of the most common types of primary immunodeficiency disease in children, and is an antibody deficiency disease which is seen in men.Most XLA patients carry mutations in Bruton tyrosine kinase (BTK) gene, they typically present with very low numbers of peripheral B cells and a profound deficiency of all immunoglobulin isotypes.XLA is characterized by recurrent bacterial infections within 2 years, sometimes life-threatening.The prognosis of XLA has been improved by the treatment of gammaglobulin that allow normal concentrations of serum IgG. Key words: X-linked agammaglobulinemia; Bruton tyrosine kinase gene; Mutation

Characteristics, Outcome and Pattern of Mutations in Patients with Follicular Lymphoma Who Progressed on BTK Inhibitors (Ibrutinib and acalabrutinib)

Introduction: Acalabrutinib and ibrutinib are Bruton's tyrosine kinase (BTK) inhibitors, which have revolutionized the treatment of B-cell lymphoma/leukemias such as mantle cell lymphoma (MCL) and chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) in frontline or relapsed refractory setting. Outcomes of patients with MCL and/or CLL who progressed on ibrutinib therapy are poor. Few reports have shown that ibrutinib resistant patients develop specific BTK mutations which confer resistance. We present the clinical and molecular data on patients with follicular lymphoma (FL) who have progressed on either ibrutinib based regimen or on acalabrutinib.Methods: We selected FL patients enrolled in clinical studies at our institution between 2013 and 2015 who discontinued acalabrutinib or ibrutinib for various reasons. Survival post ibrutinib discontinuation was calculated. We performed whole-exome sequencing on pre and post treatment (paired) samples of 3 FL patients (progressed on ibrutinib) using DNA extracted from formalin fixed paraffin embedded tissue samples. Library preparation and capture were performed using Agilent's SureSelect XT Human All Exon V4. Following capture the enriched libraries were pooled and sequenced in two Illumina HiSeq4000 lanes using a 75nt paired-end configuration.Results: Twenty of 55 patients discontinued treatment with BTK inhibitors; 5 came off from single agent acalabrutinib in relapsed refractory FL (RR-FL) while 15 came off from ibrutinib based regimen (4 as a single agent in RR-FL while 11 were treated with ibrutinib and rituximab in the frontline setting). These patients discontinued BTK inhibitor treatment, after a median of 2.8 months (range 0.9-22 months). Patients who received frontline ibrutinib (n=11), discontinued at a median of 2.8 months (0.9-22 months); previously treated patients discontinued BTK inhibitors at a median of 2.8 months (1.4-7.6 months). The reasons for discontinuation were as follows - 14 disease progression (3 on acalabrutinib and 11 on ibrutinib; 1 of them developed classical Hodgkin lymphoma), 2 non-responders (1 acalabrutinib and 1 ibrutinib) and 4 for other reasons (1 due to fatigue on acalabrutinib, 3 due to ibrutinib - 1 elevated liver enzymes, 1 asymptomatic atrial fibrillation another lost to follow up). Pre-treatment characteristics of the 16 patients who either progressed or were nonresponders to BTK inhibitors were - median age 59 years (range 41-75), 69% had stage 4 disease, 31% had FLIPI score of 3 or 4 and median LDH levels were 457 IU/L (range 290-754). Median follow up after discontinuation for all patients was 14.4 months (0-32 months). Eighteen patients (90%) were alive at the time of last follow up and 2 (10%) have died. Median survival (figure 1) of patients according to the causes of discontinuation was: not reached for both group of patients, those with other causes and those in progressive disease and/or non-responders.All 16 patients who progressed or not responded were treated with additional therapies. At the time of last follow up, 10/16 (62%) were responding to subsequent therapy - 5/10 (62%) achieved CR on lenalidomide-based therapies, 4/10 (40%), responded to chemoimmunotherapy and 1 patient responded to venetoclax-bendamustine and rituximab with CR. None were treated with PI3K inhibitors. WES studies showed EZH2 Y646 mutations in 2 of 3 FL patients in both pre and post treatment samples. Comparison of pre and post treatment samples on 3 patients showed multiple non-recurrent variants (2-12 per patient) in several genes in the post-treatment samples. These included DNMT3A R882H, NOTCH2 A3D and MLL E765G, all of which were noted in the post treatment sample of the patient that progressed to CHL. None of the other detected variants have been implicated in cancer. Of note, none of the samples showed BTK mutations despite adequate coverage.Conclusions: In contrast to other B-cell malignancies such as CLL and MCL, we observed that almost all FL patients who progressed on BTK inhibitors were salvageable by alternate therapies. Absence of BTK gene mutations in paired samples of 3 patients who progressed on ibrutinib suggests alternate mechanisms of drug resistance. [Display omitted] DisclosuresWang:Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Acerta Pharma: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Juno Therapeutics: Research Funding; Onyx: Research Funding; Kite Pharma: Research Funding; Asana BioSciences: Research Funding; Celgene: Research Funding; Pharmacyclics: Research Funding; BeiGene: Research Funding. Fayad:Seattle Genetics: Consultancy, Research Funding. Oki:Novartis: Research Funding. Westin:Spectrum: Membership on an entity's Board of Directors or advisory committees; Chugai: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; ProNAi: Membership on an entity's Board of Directors or advisory committees. Fowler:Gilead: Research Funding; Jannsen: Consultancy, Research Funding; Infinity: Consultancy, Research Funding; Roche: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; TG Therapeutics: Consultancy.

Clinical characteristics and genetic profiles of 174 patients with X-linked agammaglobulinemia: Report from Shanghai, China (2000-2015).

X-linked agammaglobulinemia (XLA) is a humoral primary immunodeficiency. XLA patients typically present with very low numbers of peripheral B cells and a profound deficiency of all immunoglobulin isotypes. Most XLA patients carry mutations in Bruton tyrosine kinase (BTK) gene.The genetic background and clinical features of 174 Chinese patients with XLA were investigated. The relationship between specific BTK gene mutations and severity of clinical manifestations was also examined. Mutations were graded from mild to severe based on structural and functional prediction through bioinformatics analysis.One hundred twenty-seven mutations were identified in 142 patients from 124 families, including 45 novel mutations and 82 recurrent mutations that were distributed over the entire BTK gene sequence. Variation in phenotypes was observed, and there was a tendency of association between genotype and age of disease onset.This report constitutes the largest group of patients with BTK mutations in China. A genotype–phenotype correlation was observed in this study. Early diagnosis of congenital agammaglobulinemia should be based on clinical symptoms, family history, and molecular analysis of the BTK gene.

X-Linked Agammagobulinemia in a Large Series of North African Patients: Frequency, Clinical Features and Novel BTK Mutations.

X-linked agammagobulinemia (XLA) is a primary immunodeficiency caused by Bruton's tyrosine kinase (BTK) gene defect. XLA patients have absent or reduced number of peripheral B cells and a profound deficiency in all immunoglobulin isotypes. This multicenter study reports the clinical, immunological and molecular features of Bruton's disease in 40 North African male patients. Fifty male out of 63 (male and female) patients diagnosed with serum agammaglobulinemia and non detectable to less than 2% peripheral B cells were enrolled. The search for BTK gene mutations was performed for all of them by genomic DNA amplification and Sanger sequencing. We identified 33 different mutations in the BTK gene in 40 patients including 12 missense mutations, 6 nonsense mutations, 6 splice-site mutations, 5 frameshift, 2 large deletions, one complex mutation and one in-frame deletion. Seventeen of these mutations are novel. This large series shows a lower frequency of XLA among male patients from North Africa with agammaglobulinemia and absent to low B cells compared with other international studies (63.5% vs. 85%). No strong evidence for genotype-phenotype correlation was observed. This study adds to other reports from highly consanguineous North African populations, showing lower frequency of X-linked forms as compared to AR forms of the same primary immunodeficiency. Furthermore, a large number of novel BTK mutations were identified and could further help identify carriers for genetic counseling.

A novel BTK gene mutation creates a de-novo splice site in an X-linked agammaglobulinemia patient

Bruton's tyrosine kinase (BTK), encoded by the BTK gene, is a cytoplasmic protein critical in B cell development. Mutations in the BTK gene cause X-linked agammaglobulinemia (XLA), a primary immunodeficiency with characteristically low or absent B cells and antibodies. This report describes a five year-old boy who presented with otitis externa, arthritis, reduced immunoglobulins and no B cells. Flow cytometry showed undetectable monocyte BTK expression. Sequencing revealed a novel mutation at exon 13 of the BTK gene which created a de novo splice site with a proximal 5 nucleotide loss resulting in a truncated BTK protein. The patient still suffered from ear infection despite intravenous immunoglobulin replacement therapy. In this study, mosaicism was seen only in the mother's genomic DNA. These results suggest that a combination of flow cytometry and BTK gene analysis is important for XLA diagnosis and carrier screening.

Clinical and mutational features of Vietnamese children with X-linked agammaglobulinemia.

BackgroundX-linked agammaglobulinemia (XLA) is a primary immune deficiency characterized by recurrent bacterial infections and profoundly depressed serum immunoglobulin levels and circulating mature B cells. It is caused by mutations of the Bruton tyrosine kinase (BTK) gene and is the most common form of inherited antibody deficiency. To our knowledge, this is the first report of XLA from Vietnam.MethodsWe investigated the BTK gene mutations and clinical features of four unrelated Vietnamese children.ResultsThe mean ages at onset and at diagnosis were 2.5 and 8 years, respectively. All patients had a medical history of otitis media, pneumonia, and septicemia at the time of diagnosis. Other infections reported included sinusitis, bronchiectasis, arthritis, skin infections, meningitis, and recurrent diarrhea. We identified one previously reported mutation (c.441G >A) and three novel mutations: two frameshifts (c.1770delG and c.1742 delG), and one nonsense (c.1249A >T).ConclusionsThe delayed diagnosis may be attributable to insufficient awareness of this rare disease on the background of frequent infections even in the immunocompetent pediatric population in Vietnam. Our results further support the importance of molecular genetic testing in diagnosis of XLA.

Index of Suspicion

* ALT: : alanine aminotransferase AST: : aspartate aminotransferase BUN: : blood urea nitrogen CBC: : complete blood count CNS: : central nervous system CSF: : cerebrospinal fluid CT: : computed tomography ECG: : electrocardiography ED: : emergency department EEG: : electroencephalography ESR: : erythrocyte sedimentation rate GI: : gastrointestinal GU: : genitourinary Hct: : hematocrit Hgb: : hemoglobin MRI: : magnetic resonance imaging WBC: : white blood cell An 11-year-old boy presents to the emergency department with a 1-week history of frequent episodes of nonbloody, nonbilious emesis associated with diarrhea and abdominal cramping. He has urgency and fecal incontinence. He has been afebrile and denies any rashes, joint pain, sick contacts, headaches, or other symptoms. On further questioning, his mother reveals that he has had 2 similar episodes of abdominal distension and diarrhea during the past 6 to 7 years. Between these episodes, she states that he normally has nonbloody, hard stools accompanied by straining and chronic abdominal pain and pain with defecation. When asked specifically, his mother does not remember when he passed his first stool after he was born. On physical examination, his temperature is 37.6°C, pulse is 100 beats per minute, respiratory rate is 16 breaths per minute, blood pressure is 113/62 mm Hg, oxygen saturation is 100% on room air, height is 63 inches (95%), and weight is 36.7 kg (25%). He has abdominal distention and diffuse abdominal tenderness with voluntary guarding. There is palpable stool in the left quadrant. There is no perianal erythema or skin tag, and rectal examination reveals a low anal tone. A CT scan of the abdomen (Figure 1) reveals a markedly distended rectosigmoid colon with circumferential, confluent, and contiguous mural thickening. Basic metabolic profile, CBC, and urinalysis results are unremarkable, but the C-reactive protein level is elevated at 131 mg/L (1248 nmol/L). Because of the concern for enterocolitis, he is empirically given broad-spectrum intravenous antibiotics and transferred to a children’s hospital for further evaluation. Figure 1. A CT scan of the abdomen shows a markedly distended rectosigmoid colon with circumferential mural thickening. A 4-year-old boy presents for evaluation of intermittent fevers of 4 weeks’ duration after 2 separate antibiotic courses prescribed for acute otitis media. He has experienced clear rhinorrhea and …

A new mutation that predicted a drastic alteration of the BTK protein function

X-linked agammaglobulinemia (XLA) or Bruton disease is a relatively rare constitutionally immune disorder due to a genetic mutation of BTK (Bruton tyrosine kinase) gene which encodes for BTK protein. BTK is a signal-transducing protein expressed in hematopoietic lineages. The genetic disorder is responsible for B cell lymphocytes' maturation arrest. The humoral immunodeficiency caused by BTK mutation is linked with recurrent bacterial and viral infections. Genetic investigations of the prepositus as well as the other members of the family are necessary to characterize a mutation in BTK gene to confirm the diagnosis and reveal a hereditary transmission or de novo mutation.Authors propose and comment a case report of an 8month old child who suffers from Bruton disease. Initial presentation was neutropenia, but genetic investigation has revealed a previously non-reported mutation in the BTK gene. The same mutation was found in the mother with low expression of BTK in monocytes and normal in B-cells suggesting a lineage specific extinction of BTK which has never been reported before.

Clinical features and mutation analysis of X-linked agammaglobulinemia in 20 Chinese patients

X-linked agammagobulinemia (XLA) is a primary immunodeficiency caused by Bruton's tyrosine kinase (BTK) gene mutation. XLA patients have an extremely small amount of peripheral B cells and profound deficiency in all immunoglobulin isotypes. We analyzed the clinical, immunologic, and molecular characteristics of children with XLA in an attempt to improve the diagnosis and treatment of XLA in China. Twenty children with XLA-compatible phenotypes from 18 unrelated families were enrolled in this study. The BTK gene was amplified and sequenced, followed by mutation analysis in these children and their female relatives. Eighteen different mutations of the BTK gene were identified in the 20 patients. Eleven mutations had been reported previously including eight missense mutations (c.994C>T, c.1987C>A, c.1885G>T, c.502T>C, c.1085C>T, c.1816C>T, c.214C>T, c.1912G>A) and three nonsense mutations (c.1267T>A, c.1793C>G, c.1618C>T). Seven novel mutations of the BTK gene were also presented and included five missense mutations (c.134T>A, c.1646T>A, c.1829C>G, c.711G>T, c.1235G>A), one splice-site mutation (c.523+1G>A) and one insertion mutation (c.1024-1025in sTTGCTAAAGCAACTGCTAAAGCAAG). Eight out of 18 mutations of the BTK gene were located in the TK domain, 4 in the PH domain, 4 in the SH2 domain and 2 in the TH domain. Genetic study for carrier status was carried out in 18 families with definite BTK gene mutations. Nine carriers with BTK gene mutations were identified. Six families without carriers were detected, and 3 patients were not tested in this study. Our results support that molecular genetic testing represents an important tool for early confirmed diagnosis of congenital agammaglobulinemia and may allow accurate carrier detection and prenatal diagnosis.

Clinical Characteristics and Molecular Analysis of 21 Chinese Children with Congenital Agammaglobulinemia

Congenital agammaglobulinemia is a humoral primary immunodeficiency and affected patients have extremely low levels of peripheral B cells and profound deficiency of all immunoglobulin isotypes. Mutations of the Bruton's tyrosine kinase (BTK) gene are responsible for most of the congenital agammaglobulinemia. In this study, the phenotypes of congenital agammaglobulinemia were investigated in 21 male children from 21 unrelated Chinese families. Sixteen different mutations of BTK gene were identified in 18 patients, and three patients did not have BTK gene mutations. Nine mutations had been reported previously including one gross deletion (c.722_2041del), one missense mutation (c.1764G>T), three non-sense mutations (c.194C>A, c.895C>T and c.1821G>A) and four invariant splice-site mutations (c.971+2T>C, c.1481+2T>A, c.1482-2A>G, c.1699-2A>G). Seven novel mutations were identified (c.373_441del, c. 504delG, c.537delC, c.851delA, c.1637G>A, c.1879T>C and c. 1482_1882 del). Ten of the eighteen mutations of BTK gene were located in the TK domain, four in the PH domain, three in the SH3 domain and one spanned the TH, SH3, SH2 and TK domain. Candidate genes of autosomal-recessive agammaglobulinemia, including IGHM, CD79a, CD79b and IGLL1, were screened in three patients without mutations in the BTK gene. A compound heterozygosity mutation in the IGHM gene (c.1956G>A, c.175_176insC) was identified in one patient. The results of our study further support that molecular genetic testing represents an important tool for early confirmed diagnosis of congenital agammaglobulinemia and may allow accurate carrier detection and prenatal diagnosis.

Preimplantation genetic diagnosis for X-linked agammaglobulinemia: a case report

To report the first clinical experience of preimplantation genetic diagnosis (PGD) for X-linked agammaglobulinemia (XLA), which resulted from a point mutation in Bruton's tyrosine kinase (BTK) gene. Case report. Clinical IVF laboratory. A couple carrying BTK gene mutation (c.832C>T) that is associated with XLA. Day 3 embryos, obtained by IVF with intracytoplasmic sperm injection, underwent blastomere biopsy and DNA testing via nest polymerase chain reaction and restriction enzyme analysis to detect the presence of a maternal BTK mutation. Successful PGD for a BTK gene mutation and transfer of healthy embryos. The patient received two PGD cycles. In total, 19 oocytes were fertilized, 15 embryos were suitable for embryo biopsy, 6 were diagnosed as unaffected, 6 were carriers, 2 were mutant, and the remaining 1 did not provide any diagnosis. In two treatment cycles, two ETs of three embryos each were performed. Unfortunately no pregnancy was achieved. We are the first to report a case of PGD for XLA. The result indicates that PGD is feasible for this genetic disease and may represent a viable alternative to prenatal diagnosis with the subsequent option of terminating an affected pregnancy.

Analysis of clinical presentations of Bruton disease: a review of 20 years of accumulated data from pediatric patients at Severance Hospital.

PurposeX-linked agammaglobulinemia (XLA) is a humoral immunodeficiency disease caused by a mutation in the Bruton tyrosine kinase (BTK) gene resulting in defective B cell differentiation. Because it is a relatively rare disorder, it is difficult for clinicians to have a comprehensive understanding of XLA due to a lack of exposure to the disease. Clinical presentations of patients with XLA were analyzed and discussed to improve care plans.Materials and MethodsDuring a 20 year period, from January 1987 to June 2006, a total of 19 patients were diagnosed as XLA in the Department of Pediatrics at Severance Hospital, Seoul, Korea. A retrospective analysis of the clinical presentations of those patients was performed.ResultsThe mean age of the XLA patients included in the study was 4.89 years, with a range of 6 months to 13 years. Twelve patients were diagnosed before age 5, while the other 7 patients were diagnosed after age 5. Recurrent infections observed in the patients included pneumonia, acute otitis media, septic arthritis, skin infection, sepsis, sinusitis, acute gastroenteritis, cervical lymphadenitis, epididymitis, meningitis, osteomyelitis, urinary tract infection and encephalitis. Frequency of admissions was variable from 0 to 12 times, depending on the time at which immunoglobulin therapy was started. Six cases had family histories positive for XLA. BTK gene mutations were found in 8 cases.ConclusionThe overall prognosis of XLA is good as long as patients are diagnosed and treated early with regular intra venous gamma globulin therapy before the sequelae of recurrent infections appear.

Screening of the Bruton Tyrosine Kinase (BTK) Gene Mutations in 13 Iranian Patients with Presumed X-Linked Agammaglobulinemia.

X-linked agammaglobulinemia (XLA) is an immunodeficiency caused by mutations in the Bruton tyrosine kinase (Btk) gene. In order to identify the mutations in Btk gene in Iranian patients with antibody deficiency, 13 male patients with an XLA phenotype from 11 unrelated families were enrolled as the subjects of investigation for Btk mutation analysis using PCR-SSCP followed by sequencing. Five different mutations were identified in 5 patients from 5 unrelated families. Three mutations had been reported previously including TTTG deletion in intron 15 (4 bps upstream of exon 16 boundary), nonsense point mutation (1896G>A) that resulted in a premature stop codon (W588X) in kinase domain, and nucleotide alteration in invariant splice donor site of exon12 (IVS12+1G>A). While 2 novel missense mutations (2084A>G, 1783T>C) were identified leading to amino acid changes (I651T, Y551H). The results of this study further support the notion that molecular genetic testing represents an important tool for definitive and early diagnosis of XLA and may allow accurate carrier detection and prenatal diagnosis.