Ataxia Telangiectasia Patients Research Articles

Regulation of transcription patterns, poly(ADP-ribose), and RNA-DNA hybrids by the ATM protein kinase

The ataxia telangiectasia mutated (ATM) protein kinase is a master regulator of the DNA damage response and also an important sensor of oxidative stress. Analysis of gene expression in ataxia-telangiectasia (A-T) patient brain tissue shows that large-scale transcriptional changes occur in patient cerebellum that correlate with the expression level and guanine-cytosine (GC) content of transcribed genes. In human neuron-like cells in culture, we map locations of poly(ADP-ribose) and RNA-DNA hybrid accumulation genome-wide with ATM inhibition and find that these marks also coincide with high transcription levels, active transcription histone marks, and high GC content. Antioxidant treatment reverses the accumulation of R-loops in transcribed regions, consistent with the central role of reactive oxygen species in promoting these lesions. Based on these results, we postulate that transcription-associated lesions accumulate in ATM-deficient cells and that the single-strand breaks and PARylation at these sites ultimately generate changes in transcription that compromise cerebellum function and lead to neurodegeneration over time in A-T patients.

Patient-Reported Outcomes and Medical Provider Satisfaction Among Adult and Pediatric Ataxia-Telangiectasia Patients.

Ataxia-telangiectasia (A-T) is a rare genetic condition with malfunctioning DNA repair processes resulting in significant clinical findings, including progressive neurologic decline, elevated malignancy risk, immunodeficiency, oculocutaneous telangiectasias, and severe pulmonary disease. Research has been limited into the quality of life of such patients and yet to be completed are studies quantitatively analyzing psychosocial, physical, and cognitive patient-reported outcomes (PROs) within the A-T population. PRO evaluations of 90 international adult and pediatric A-T patients and their caregivers were completed via secure online administration of Patient-Reported Outcomes Measurement Information System (PROMIS) short forms evaluating anger, cognition, mood, social health, fatigue, pain, anxiety, and upper extremity function. The impact of age, gender, race/ethnicity, prior malignancy diagnosis, and current supportive treatment interventions on such PROs was additionally assessed. Finally, given the importance of medical providers in the care of A-T patients and the impact of patient satisfaction on healthcare outcomes, we further analyzed, via a novel survey, how patients and caregivers perceived their primary A-T healthcare provider's A-T expertise, trustworthiness, accessibility, and level of compassion. It was found that a diagnosis of A-T complexly impacts patient PROs, but such data offers the potential for preventative and therapeutic interventions to improve the care of such patients. While most A-T patients and their caregivers feel their primary A-T medical provider has expertise and compassion in addition to being accessible and trustworthy, a significant percentage of study subjects did not agree that their provider was an expert in A-T or overall trustworthy.

Incidence and Prognosis of Primary Malignancies in Ataxia-Telangiectasia Patients: A Report from the Ataxia-Telangiectasia Clinical Center (ATCC)

Biallelic germline mutations in the ATM gene result in Ataxia-Telangiectasia (AT), a classic DNA repair disorder associated with a high incidence of primary malignancies. The lack of standardized cancer treatment approaches for patients with AT is believed to contribute to poor survival after diagnosis. Robust characterization of the incidence, outcomes, and ATM variant enrichment of large cohorts of individuals with AT who develop malignancies are needed to inform therapeutic decision-making. The AT Clinical Center (ATCC) at Johns Hopkins Hospital is a large, retrospective cohort that prospectively collects outcomes data on individuals diagnosed with AT in the US. Standardized incidence ratios (SIRs) were used to compare cancer incidence to that of age-, sex-, and year-matched US general population using the SEER database. Standardized mortality ratios (SMRs) and mortality rate ratios were used to estimate mortality risk compared to the general population. Among 508 total participants with AT, 84 developed cancers (16.5%): 39 non-Hodgkin lymphoma (NHL), 7 Hodgkin lymphoma, 16 leukemia (n=13 of T cell origin), and 22 carcinomas. SIRs were 355.9, 67.4, 45.6, and 18.0, respectively. Median (interquartile range) age at cancer diagnosis was 14.3 years (10.3-22.8), with NHL occurring in the youngest (12.4 years, IQR 7.3-16.7) and solid tumors in the oldest (26.3 years, IQR 18.7-29.0) individuals. The SMR was 24.6 (95% CI: 21.1-28.4) for the overall cohort of AT patients and 232.9 (95% CI: 178.1-299.2) among those with cancer. Median survival following a cancer diagnosis was 2.5 years (95% CI: 0.1-14.4). The post-cancer mortality rate ratio was 2.2 (95% CI: 1.1-4.3, p=0.025) comparing AT patients with cancer treated without dose reduction or for whom dosing was unknown (n=24) versus AT patients with cancer who received dose reduced chemotherapy (n= 38). Among those who received chemotherapy (n=62), 11/24 (45.8%, 95% CI: 25.6-67.2) treated with standard dosing and 24/38 (63%, 95% CI: 46.0-78.2) treated with reduced dosing experienced toxicity (p=0.20). ATM variant associations were detected by single variant analysis among 247 patients with AT who had confirmed biallelic ATM mutations via whole exome sequencing. Individuals with AT are at very high-risk of primary malignancies, of which NHL is most common. Prognosis is poor regardless of standard versus dose reduced chemotherapy regimens, which calls for novel therapies.

Disproportionate Expression of ATM in Cerebellar Cortex During Human Neurodevelopment

Cerebellar neurodegenerationis a classical feature of ataxia telangiectasia (A-T), an autosomal recessive condition caused by loss-of-function mutation of the ATM gene, a gene with multiple regulatory functions. The increased vulnerability of cerebellar neurones to degeneration compared to cerebral neuronal populations in individuals with ataxia telangiectasia implies a specific importance of intact ATM function in the cerebellum. We hypothesised that there would be elevated transcription of ATM in the cerebellar cortex relative to ATM expression in other grey matter regions during neurodevelopment in individuals without A-T. Using ATM transcription data from the BrainSpan Atlas of the Developing Human Brain, we demonstrate a rapid increase in cerebellar ATM expression relative to expression in other brain regions during gestation and remaining elevated during early childhood, a period corresponding to the emergence of cerebellar neurodegeneration in ataxia telangiectasia patients. We then used gene ontology analysis to identify the biological processes represented in the genes correlated with cerebellar ATM expression. This analysis demonstrated that multiple processes are associated with expression of ATM in the cerebellum, including cellular respiration, mitochondrial function, histone methylation, and cell-cycle regulation, alongside its canonical role in DNA double-strand break repair. Thus, the enhanced expression of ATM in the cerebellum during early development may be related to the specific energetic demands of the cerebellum and its role as a regulator of these processes.

Exploration of clinical and genetic findings in Ataxia-Telangiectasia (AT) patients from the Indian subcontinent

BackgroundAtaxia-Telangiectasia (AT) is a rare autosomal recessive neurodegenerative disorder. It is caused by mutations in the Ataxia-Telangiectasia mutated (ATM) gene, which codes for protein ATM serine/threonine kinase. ObjectiveWe aim to describe the clinical and radiological findings in children and adolescents of 20 molecularly confirmed cases of AT. We aim to correlate these findings with the genotype identified among them. MethodsThis retrospective study included 20 patients diagnosed clinically and genetically with AT over 10 years. The clinical, radiological and laboratory data were extracted from the hospital's electronic medical records. Molecular testing was done using next generation sequencing and Sanger sequencing. In silico predictions were performed for the variants identified by applying Cryp-Skip, Splice site prediction by Neural Network, Mutation Taster and Hope prediction tool. ResultsConsanguinity was documented in nearly half of the patients. Telangiectasia was absent in 10%. Microcephaly was seen in 40% cases. The incidence of malignancy in our study population was low. Molecular testing done in the 18 families (20 patients) identified 23 variants of which ten were novel. Biallelic homozygous variants were noted in 13 families and compound heterozygous in 5 families. Out of the 13 families who were homozygous, 8 families (61.5%) (9 patients) have history of consanguinity. In silico prediction of novel missense variants, NM_000051.4 (ATM_v201): c.2702T > C showed disruption of the α-helix of ATM protein and NM_000051.4 (ATM_v201): c.6679C > G is expected to disturb the rigidity of protein structure in the FAT domain. The four novel splice site variants and two intronic variants result in exon skipping as predicted by Cryp-Skip. ConclusionsAT should be confirmed by molecular testing in young-onset cerebellar ataxia, even without telangiectasia. Awareness of this rare disease will facilitate study of larger cohorts from Indian population to characterize variants and determine its prevalence in this population.

LINE-1 activation in the cerebellum drives ataxia

Dysregulation of long interspersed nuclear element 1 (LINE-1, L1), a dominant class of transposable elements in the human genome, has been linked to neurodegenerative diseases, but whether elevated L1 expression is sufficient to cause neurodegeneration has not been directly tested. Here, we show that the cerebellar expression of L1 is significantly elevated in ataxia telangiectasia patients and strongly anti-correlated with the expression of epigenetic silencers. To examine the role of L1 in the disease etiology, we developed an approach for direct targeting of the L1 promoter for overexpression in mice. We demonstrated that L1 activation in the cerebellum led to Purkinje cell dysfunctions and degeneration and was sufficient to cause ataxia. Treatment with a nucleoside reverse transcriptase inhibitor blunted ataxia progression by reducing DNA damage, attenuating gliosis, and reversing deficits of molecular regulators for calcium homeostasis in Purkinje cells. Our study provides the first direct evidence that L1 activation can drive neurodegeneration.

Drug Sensitivity of Vaccine-Derived Rubella Viruses and Quasispecies Evolution in Granulomatous Lesions of Two Ataxia-Telangiectasia Patients Treated with Nitazoxanide.

A strong association between rubella virus (RuV) and chronic granulomas, in individuals with inborn errors of immunity, has been recently established. Both the RA27/3 vaccine and wild-type RuV strains were highly sensitive to a broad-spectrum antiviral drug, nitazoxanide (NTZ), in vitro. However, NTZ treatment, used as a salvage therapy, resulted in little or no improvements of RuV-associated cutaneous granulomas in patients. Here, we report investigations of possible causes of treatment failures in two ataxia-telangiectasia patients. Although a reduction in RuV RNA in skin lesions was detected by real-time RT-PCR, live immunodeficiency-related vaccine-derived rubella viruses (iVDRV) were recovered from granulomas, before and after the treatments. Tizoxanide, an active NTZ metabolite, inhibited replications of all iVDRVs in cultured A549 cells, but the 50% and 90% inhibitory concentrations were 10–40 times higher than those for the RA27/3 strain. There were no substantial differences in iVDRV sensitivities, neither before nor after treatments. Analysis of quasispecies in the E1 gene, a suspected NTZ target, showed no effect of NTZ treatments on quasispecies’ complexity in lesions. Thus, failures of NTZ therapies were likely due to low sensitivities of iVDRVs to the drug, and not related to the emergence of resistance, following long-term NTZ treatments.

Clinical Manifestations of Ataxia-Telangiectasia with Class Switch Recombination Defect

Background: Elevated serum levels of IgM and recurrent infections, mainly respiratory tract infections, could be the presenting features in some ataxia-telangiectasia (AT) patients, and may initially be misdiagnosed as hyper-IgM (HIgM) syndrome. Class switch recombination (CSR), which is defective in HIgM syndrome, is an important mechanism in the maturation of B lymphocytes to produce different isotypes of antibodies in response to antigen stimulation. Methods: The clinical manifestations and laboratory findings of 16 cases with low IgA and IgG levels, and normal to elevated IgM levels with CSR defect are reported. Results: In 16 cases, the median age at onset of the diseases, and median age at the time of the diagnosis were 1 year (interquartile range [IQR] = 1.6), and 4 years (IQR = 3.1), respectively. Two of the patients (12.5 %) died due to respiratory infection. In this study, Out of the studied population, four were male (25%), and 12 were female (75%). Most of the patients had consanguineous parents (81.3 %). All of the patients had ataxia, and 15 patients had telangiectasia (93.8 %), and one of the cases had malignancy (dermatofibroma). Also, 15 patients presented infections (93.8 %). Autoimmunity was seen in three patients (18.8 %). In addition, some of the patients manifested hepatosplenomegaly (31.3 %) and thrombocytopenia (18.8 %). Neurological manifestations, such as visual impairment (12.5 %), epilepsy (6.3 %), and tremor (12.5 %), were also present. Conclusion: AT patients with HIgM phenotype and CSR defect, compared to other AT patients, may present different clinical manifestations, such as various infections. Considering their manifestations, the management and treatment of these patients are necessary.

Oxidative Damage Induced Telomere Mediated Genomic Instability in Cells from Ataxia Telangiectasia Patients.

Our cellular genome is susceptible to cytotoxic lesions which include single strand breaks and double strand breaks among other lesions. Ataxia telangiectasia mutated (ATM) protein was one of the first DNA damage sensor proteins to be discovered as being involved in DNA repair and as well as in telomere maintenance. Telomeres help maintain the stability of our chromosomes by protecting the ends from degradation. Cells from ataxia telangiectasia (AT) patients lack ATM and accumulate chromosomal alterations. AT patients display heightened susceptibility to cancer. In this study, cells from AT patients (called as AT -/- and AT +/- cells) were characterized for genome stability status and it was observed that AT -/- cells show considerable telomere attrition. Furthermore, DNA damage and genomic instability were compared between normal (AT +/+ cells) and AT -/- cells exhibiting increased frequencies of spontaneous DNA damage and genomic instability markers. Both AT -/- and AT +/- cells were sensitive to sodium arsenite (1.5 and 3.0 μg/ml) and ionizing radiation-induced (2 Gy, gamma rays) oxidative stress. Interestingly, telomeric fragments were detected in the comet tails as revealed by comet-fluorescence in situ hybridization analysis, suggestive of telomeric instability in AT -/- cells upon exposure to sodium arsenite or radiation. Besides, there was an increase in the number of chromosome alterations in AT -/- cells following arsenite treatment or irradiation. In addition, complex chromosome aberrations were detected by multicolor fluorescence in situ hybridization in AT -/- cells in comparison to AT +/- and normal cells. Telomere attrition and chromosome alterations were detected even at lower doses of sodium arsenite. Peptide nucleic acid - FISH analysis revealed defective chromosome segregation in cells lacking ATM proteins. The data obtained in this study substantiates the role of ATM in telomere stability under oxidative stress.

X-Linked TLR7 Deficiency Underlies Critical COVID-19 Pneumonia in a Male Patient with Ataxia-Telangiectasia

BackgroundCoronavirus disease 2019 (COVID-19) exhibits a wide spectrum of clinical manifestations, ranging from asymptomatic to critical conditions. Understanding the mechanism underlying life-threatening COVID-19 is instrumental for disease prevention and treatment in individuals with a high risk.ObjectivesWe aimed to identify the genetic cause for critical COVID-19 pneumonia in a patient with a preexisting inborn error of immunity (IEI).MethodsSerum levels of specific antibodies against the virus and autoantibodies against type I interferons (IFNs) were measured. Whole exome sequencing was performed, and the impacts of candidate gene variants were investigated. We also evaluated 247 ataxia-telangiectasia (A-T) patients in the Iranian IEI registry.ResultsWe report a 7-year-old Iranian boy with a preexisting hyper IgM syndrome who developed critical COVID-19 pneumonia. IgM only specific COVID-19 immune response was detected but no autoantibodies against type I IFN were observed. A homozygous deleterious mutation in the ATM gene was identified, which together with his antibody deficiency, radiosensitivity, and neurological signs, established a diagnosis of A-T. Among the 247 A-T patients evaluated, 36 had SARS-CoV-2 infection, but all had mild symptoms or were asymptomatic except the index patient. A hemizygous deleterious mutation in the TLR7 gene was subsequently identified in the patient.ConclusionsWe report a unique IEI patient with combined ATM and TLR7 deficiencies. The two genetic defects underlie A-T and critical COVID-19 in this patient, respectively.

Genetic Risk Variants for Class Switching Recombination Defects in Ataxia-Telangiectasia Patients

BackgroundAtaxia-telangiectasia (A-T) is a rare autosomal recessive disorder caused by mutations in the ataxia telangiectasia mutated (ATM) gene. A-T patients manifest considerable variability in clinical and immunological features, suggesting the presence of genetic modifying factors. A striking heterogeneity has been observed in class switching recombination (CSR) in A-T patients which cannot be explained by the severity of ATM mutations.MethodsTo investigate the cause of variable CSR in A-T patients, we applied whole-exome sequencing (WES) in 20 A-T patients consisting of 10 cases with CSR defect (CSR-D) and 10 controls with normal CSR (CSR-N). Comparative analyses on modifier variants found in the exomes of these two groups of patients were performed.ResultsFor the first time, we identified some variants in the exomes of the CSR-D group that were significantly associated with antigen processing and presentation pathway. Moreover, in this group of patients, the variants in four genes involved in DNA double-strand breaks (DSB) repair signaling, in particular, XRCC3 were observed, suggesting an association with CSR defect.ConclusionAdditional impact of certain variants, along with ATM mutations, may explain the heterogeneity in CSR defect phenotype among A-T patients. It can be concluded that genetic modulators play an important role in the course of A-T disease and its clinical severity.

Functions of NK and iNKT cells in pediatric and adult CVID, ataxia telangiectasia and agammaglobulinemia patients

Primary immune deficiencies (PID) are known to be more than 400 genetic defects caused by the impairment in development and/or functions of the immune system. Common Variable Immunodeficiency (CVID), Ataxia Telangiectasia (AT) and Agammaglobulinemia (AG) are examples of the most common immunodeficiency syndrome. Natural killer (NK) cells are a component of innate immune system and play a major role in the host-rejection of both tumors and virally infected cells. iNKT cells have a role in autoimmune and infectious diseases and controlling of tumor rejection. In this study, NK and iNKT cells and their functions, and intracellular cytokine amount are aimed to determine in patients that suffer CVID, AT and AG. NKp30, NKp46, NKG2D, perforin and granzyme mRNA expression levels were analyzed using RT-PCR. Receptors, cytokine amount of NK cell subset and iNKT were analyzed by flow cytometry. Decreased CD3+ T and elevated NK cell subset in pediatric AT were found. Expression of NKp44 was decreased in adult AG, but not in pediatric patients. Low NKp44 expression in CD3−CD16+CD56dim NK cell subset was found in pediatric AT patients. High HLA-DR, perforin and granzyme expression were found in CD3−CD16+CD56dim NK cell subset of pediatric CVID and AT patients. Alteration of the number of NK subsets, NK receptor expression and cytokine production were observed in pediatric patients compared to healthy subjects.

Parents of ataxia-telangiectasia patients display a distinct cellular immune phenotype mimicking ATM-mutated patients.

Heterozygous relatives of ataxia-telangiectasia (AT) patients are at an increased risk for certain AT-related manifestations. We also show that there is an increase of infection frequency in parents of AT patients. Thus, we hypothesized that the parents might exhibit immune alterations similar to their affected children. Lymphocyte phenotyping to enumerate T- and B-cell subsets was performed. Functional analyses included in vitro quantified γ-H2AX, poly (ADP-ribose) polymerase(PARP) and caspase-9 proteins. Chromosomal instability was determined by comet assay. We analyzed 20 AT patients (14F/6M), 31 parents (16F/15M), and 35 age-matched healthy controls. The AT patients' parents exhibited low frequency of naive CD4+ T- (n=14, 45%) and recent thymic emigrants (n=11, 35%) in comparison with the age-matched healthy donors. Interestingly, parents with low naive T cells also demonstrated high rate of recurrent infections (9/14, 64%). In comparison with age-matched controls, parents who had recurrent infections and low naive T cells showed significantly higher baseline γ-H2AX levels and H2 O2 -induced DNA damage as well as increased cleaved caspase-9 and PARP proteins. Parents of AT patients could present with recurrent infections and display cellular defects that mimic AT patients. The observed immunological changes could be associated with increased DNA double-strand breaks.

TREC and KREC profiling as a representative of thymus and bone marrow output in patients with various inborn errors of immunity.

Primary immune deficiency (PID) disorders are clinically and molecularly heterogeneous diseases. T cell receptor excision circles (TRECs) and κ (kappa)-deleting excision circles (KRECs) are markers of T and B cell development, respectively. They are useful tools to assess T and B cell function and immune reconstitution and have been used for newborn screening for severe combined immunodeficiency disease (SCID) and agammaglobulinemia, respectively. Their profiles in several genetically confirmed PIDs are still lacking. The objective of this study was to determine TREC and KREC genomic profiling among various molecularly confirmed PIDs. We used real-time-quantitative polymerase chain reaction (RT-qPCR)-based triplex analysis of TRECs, KRECs and β-actin (ACTB) in whole blood genomic DNA isolated from 108 patients with molecularly confirmed PIDs. All agammaglobulinemia patients had low KREC counts. All SCIDs and Omenn syndrome patients secondary to mutations in RAG1, RAG2, DCLRE1C and NHEJ1 had low TREC and KREC counts. JAK3-deficient patients had normal KREC and the TREC count was influenced by the type of mutation. Early-onset ADA patients had low TREC and KREC counts. Four patients with zeta-chain-associated protein kinase 70 (ZAP70) had low TREC. All purine nucleoside phosphorylase (PNP) patients had low TREC. Combined immunodeficiency (CID) patients secondary to AK2, PTPRC, CD247, DCLREC1 and STAT1 had normal TREC and KREC counts. Most patients with ataxia-telangiectasia (AT) patients had low TREC and KREC, while most DOCK8-deficient patients had low TRECs only. Two of five patients with Wiskott-Aldrich syndrome (WAS) had low TREC counts as well as one patient each with bare lymphocyte syndrome (BLS) and chronic granulomatous disease. All patients with Griscelli disease, Chediak-Higashi syndrome, hyper-immunoglobulin (Ig)M syndrome and IFNGR2 had normal TREC and KREC counts. These data suggest that, in addition to classical SCID and agammaglobulinemia, TREC/KREC assay may identify ZAP70 patients and secondary target PIDs, including dedicator of cytokinesis 8 (DOCK8) deficiency, AT and some individuals with WAS and BLS.

Evaluation of Radiation Sensitivity in Patients with Hyper IgM Syndrome

ABSTRACT Background HIGM syndrome is a rare form of primary immunodeficiencies characterized by normal/increased amounts of serum IgM and decreased serum levels of other switched immunoglobulin classes. Since the affected patients are continuously infected with various types of pathogens and are susceptible for cancers, diagnostic and therapeutic tests including imaging techniques are recommended for the diagnosis and treatment of these patients, which predispose them to higher accumulated doses of radiation. Given the evidence of class switching recombination machinery defect and its association with an increased rate of DNA repair, we aimed to evaluate radiation sensitivity among a group of patients diagnosed with HIGM syndrome. Methods 19 HIGM patients (14 CD40 L and 3 AID deficiencies and 2 unsolved cases without known genetic defects) and 17 control subjects (10 healthy subjects as negative control group, 7 ataxia-telangiectasia patients as positive control group) were enrolled. G2 assay was carried out for the determination of radiosensitivity. Results Based on radiation-induced chromosomal changes among the studied HIGM patients and their comparison with the controls, almost all (95%) the patients had degrees of radiosensitivity: 6 patients with low to moderate, 1 patient with moderate, 11 patients with severe and 1 patient without radiation sensitivity. Conclusion Today, X-ray radiation plays a very important role in diagnostic and therapeutic procedures; while increased exposure has devastating effects especially in radiosensitive patients. Considering higher sensitivity in HIGM patients, utilizing radiation-free techniques could partly avoid unnecessary and high-level exposure to radiation, thus preventing or reducing its harmful effects on the affected patients.

Differential survival requirements for Lck- and CD3e-dependent signaling defines two populations of ATMKO thymic T cell lymphomas

Abstract The product of theataxia-telangiectasia mutated gene (ATM) is a serine-threonine kinase thatcommunicates between molecules that detect dangerous DNA double strand breaksand effector mechanisms that maintain genomic integrity. ATM deficiency in bothhumans and mice is associated with genomic instability and increased malignancies. ATMKO mice exclusively develop thymic T cell lymphomas that resemble thymically-derivedT-ALL that occur in human ATM-deficient ataxia telangiectasia patients. Flowcytometry identified two subsets of ATMKO T cell lymphomas based on surfaceexpression of CD3ɛ, TCRβ and pre-Tα:Cells that express surface CD3ɛ, TCRβ and pre-Tα(surface receptor high; sRhi) and cells that do not express detectable surface CD3ɛ, TCRβ orpre-Tα(sRlo). When assayed for CD25 and CD44 expression sRhi lymphomas resemble DN3or DN4 cells while sRlo lymphomas resemble more immature DN1 or DN2 cells. Pre-TCRsignaling in normal DN3 and DN4 thymocytes provides an essential survivalsignal that is proposed to be constitutive and ligand-independent. Therefore, weasked if surface sRhi and sRlo cells are dependent on pre-TCR signaling byincubating cells with either Lck inhibitor, CAS 213743-31-8, or CD3ɛshRNA to inhibit pre-TCR signaling. Both treatments significantly inhibitedsurvival of sRhi lymphomas, while survival of sRlo cells was largely unaffected. These results suggest that ATMKO T celllymphomas arise from cells transformed at different stages of DN development andthat sRhigh cells, like normal DN3 and DN4 thymocytes, retain apre-TCR-dependent survival requirement. These results also suggest that pre-TCRsignaling may be a useful target for clinical intervention in treatment ofhuman T-ALL that express a pre-TCR.

Mitochondria at the crossroads of ATM-mediated stress signaling and regulation of reactive oxygen species

The Ataxia-telangiectasia mutated (ATM) kinase responds to DNA double-strand breaks and other forms of cellular stress, including reactive oxygen species (ROS). Recent work in the field has uncovered links between mitochondrial ROS and ATM activation, suggesting that ATM acts as a sensor for mitochondrial derived ROS and regulates ROS accumulation in cells through this pathway. In addition, characterization of cells from Ataxia-telangiectasia patients as well as ATM-deficient mice and cell models suggest a role for ATM in modulating mitochondrial gene expression and function. Here we review ROS responses related to ATM function, recent evidence for ATM roles in mitochondrial maintenance and turnover, and the relationship between ATM and regulation of protein homeostasis.

Features of DNA repair in dermal fibroblasts in ataxia-telangiectasia patients with mosaic type of manifestation of active ATM kinase

Cell mosaicism is found in biological systems much more often than clinically identified forms of the disease, in some cases, "erased forms” or "normal variants” are phenotypic manifestations of mosaicism. Some diseases, difficult for a clinical diagnosis, such as ataxia-telangiectasia, are based on cell mosaicism. This work is aimed to study DNA repair disorders in the cell lines of dermal fibroblasts isolated from skin biopsies of 5 patients with a clinically diagnosed ataxia-telangiectasia. In the obtained cell lines, the method of indirect immunofluorescence was used to determine the number, intensity, focus area pATMSer1981 and 53BP1, as well as the number of cells with the active form of the ATM kinase. The mosaic pattern of malfunctioning of the active form of the ATM kinase, phospho-ATM Ser1981, was revealed at different time intervals after exposure to ionizing radiation at a dose of 2 Gy. Significant differences were found between the number of ATMSer1981 and 53BP1 foci, the fluorescence intensity and their area in the cells of patients with ataxia-telangiectasia and healthy donors. The results of this work can be used in the diagnosis of ataxia-telangiec-tasia and determining the degree of impairment of the functional activity of the ATM gene.

Effect of Class Switch Recombination Defect on the Phenotype of Ataxia-Telangiectasia Patients

ABSTRACT Objectives: Ataxia-telangiectasia (A-T) is an autosomal recessive neurodegenerative disorder with multisystem involvement caused by homozygous or compound heterozygous mutations in the ataxia telangiectasia mutated (ATM) gene which encodes a serine/threonine protein kinase. The aims of this study were to investigate class switch recombination (CSR) and to review the clinical and immunologic phenotypes of 3 groups of A-T patients, including A-T patients with CSR defects (CSR-D), A-T patients with selective immunoglobulin A deficiency (IgA-D) and A-T patients with normal Ig level. Methods: In this study, 41 patients with confirmed diagnosis of A-T (16 A-T patients with HIgM, 15 A-T patients with IgA-D, and 10 A-T patients with normal Ig levels) from Iranian immunodeficiency registry center were enrolled. B-cell proliferation, in vitro CSR toward IgE and IgA were compared between three groups as well as G2 radiosensitivity assay. Results: Earliest presentation of telangiectasia was a significant hallmark in A-T patients with CSR-D (p = .036). In this investigation, we found that the frequency of respiratory infection (p = .002), pneumonia (p = .02), otitis media (p = .008), chronic fever (p < .001), autoimmunity (p = .02) and hepatosplenomegaly (p = .03) in A-T patients with HIgM phenotype were significantly higher than the other groups. As expected IgE production stimulation and IgA CSR were perturbed in HIgM patients that were aligned with the higher readiosenstivity scores in this group. Conclusion: A-T patients with HIgM compared to other A-T patients presenting more infections and noninfectious complications, therefore, early detection and careful management of these patients is necessary.

Correction of ATM mutations in iPS cells from two ataxia-telangiectasia patients restores DNA damage and oxidative stress responses.

Patients with ataxia-telangiectasia (A-T) lack a functional ATM kinase protein and exhibit defective repair of DNA double-stranded breaks and response to oxidative stress. We show that CRISPR/Cas9-assisted gene correction combined with piggyBac (PB) transposon-mediated excision of the selection cassette enables seamless restoration of functional ATM alleles in induced pluripotent stem cells from an A-T patient carrying compound heterozygous exonic missense/frameshift mutations, and from a patient with a homozygous splicing acceptor mutation of an internal coding exon. We show that the correction of one allele restores expression of ~ 50% of full-length ATM protein and ameliorates DNA damage-induced activation (auto-phosphorylation) of ATM and phosphorylation of its downstream targets, KAP-1 and H2AX. Restoration of ATM function also normalizes radiosensitivity, mitochondrial ROS production and oxidative-stress-induced apoptosis levels in A-T iPSC lines, demonstrating that restoration of a single ATM allele is sufficient to rescue key ATM functions. Our data further show that despite the absence of a functional ATM kinase, homology-directed repair and seamless correction of a pathogenic ATM mutation is possible. The isogenic pairs of A-T and gene-corrected iPSCs described here constitute valuable tools for elucidating the role of ATM in ageing and A-T pathogenesis.