Ataxia Telangiectasia


Literature Analysis

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  • Ultraviolet Rays
  • Fibroblasts
  • Cultured Cells
  • Lymphocytes
  • Adolescents
  • Ataxia Telangiectasia Mutated Proteins
  • Fanconi Anaemia
  • Transfection
  • ATM
  • Tumor Suppressor Proteins
  • DNA
  • Ataxia-telangiectasia
  • Proteins
  • Breast Cancer
  • Chromosome Mapping
  • United Kingdom
  • Risk Factors
  • Genetic Predisposition
  • Polymerase Chain Reaction
  • Cell Cycle Proteins
  • Genetic Markers
  • Heterozygote
  • Protein-Serine-Threonine Kinases
  • Mutation
  • Base Sequence
  • Karyotyping
  • DNA-Binding Proteins
  • DNA Damage
  • Chromosome Disorders
  • Chromosome Aberrations
  • Lymphoma
  • DNA Repair
  • DNA Mutational Analysis
  • Radiation Tolerance
  • Chromosome 11
  • Childhood Cancer
  • Cell Line
  • X-Rays
  • Chromosome 14
  • Genotype
Tag cloud generated 10 March, 2017 using data from PubMed, MeSH and CancerIndex

Mutated Genes and Abnormal Protein Expression (2)

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ATM 11q22.3 AT1, ATA, ATC, ATD, ATE, ATDC, TEL1, TELO1 Germline
-ATM mutation in Ataxia Telangiectasia
MTCP1 Xq28 p8MTCP1, P13MTCP1 -MTCP1 and Ataxia-telangiectasia

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Useful Links (11 links)

Latest Publications

Zhan H, Aizawa K, Sun J, et al.
Ataxia telangiectasia mutated in cardiac fibroblasts regulates doxorubicin-induced cardiotoxicity.
Cardiovasc Res. 2016; 110(1):85-95 [PubMed] Article available free on PMC after 01/05/2017 Related Publications
AIMS: Doxorubicin (Dox) is a potent anticancer agent that is widely used in the treatment of a variety of cancers, but its usage is limited by cumulative dose-dependent cardiotoxicity mainly due to oxidative damage. Ataxia telangiectasia mutated (ATM) kinase is thought to play a role in mediating the actions of oxidative stress. Here, we show that ATM in cardiac fibroblasts is essential for Dox-induced cardiotoxicity.
METHODS AND RESULTS: ATM knockout mice showed attenuated Dox-induced cardiotoxic effects (e.g. cardiac dysfunction, apoptosis, and mortality). As ATM was expressed and activated predominantly in cardiac fibroblasts, fibroblast-specific Atm-deleted mice (Atm(fl/fl);Postn-Cre) were generated to address cell type-specific effects, which showed that the fibroblast is the key lineage mediating Dox-induced cardiotoxicity through ATM. Mechanistically, ATM activated the Fas ligand, which subsequently regulated apoptosis in cardiomyocytes at later stages. Therapeutically, a potent and selective inhibitor of ATM, KU55933, when administered systemically was able to prevent Dox-induced cardiotoxicity.
CONCLUSION: ATM-regulated effects within cardiac fibroblasts are pivotal in Dox-induced cardiotoxicity, and antagonism of ATM and its functions may have potential therapeutic implications.

Mahon SM
Management of Individuals With a Mutation in the Ataxia Telangiectasia Mutated Gene.
Oncol Nurs Forum. 2016; 43(1):114-7 [PubMed] Related Publications
Advances in genetic testing have led to the identification of multiple genes associated with a hereditary risk for developing breast and other cancers. One such gene is the ataxia telangiectasia mutated (ATM) gene, which is available on many genetic panels offered to individuals with suspected hereditary risk. Genetic testing can often lead to improved understanding and clarification of risk for developing cancer, as well as allow affected individuals to make informed choices about management, including the adoption of primary prevention strategies and more aggressive screening than typically recommended in the general population. This article provides an overview of the role of mutations in the ATM gene in developing malignancies, along with emerging research on treatment implications based on genetic testing results.

Liu XL, Wang T, Huang XJ, et al.
Novel ATM mutations with ataxia-telangiectasia.
Neurosci Lett. 2016; 611:112-5 [PubMed] Related Publications
Ataxia telangiectasia is an autosomal recessive multisystem disorder characterized by progressive cerebellar ataxia with onset in childhood, oculocutaneous telangiectasia, increased serum alpha-fetoprotein, immunodeficiency, chromosomal instability, and radiation hypersensitivity. Ataxia-telangiectasia mutated gene (ATM) is one of the known genes to be associated with ataxia telangiectasia. We reported the clinical and genetic findings of three early-onset Chinese patients who demonstrated ataxia, oculomotor apraxia, choreoathetosis, myoclonus and telangiectasia of eyes. Sequence analysis of ATM revealed two known nonsense mutations c.8287C>T and c.9139C>T in the siblings. Though the siblings carried the same mutations, they showed different clinical features involving strephenopodia, exotropia, torsion dystonia, myoclonus and extrapyramidal impairments. The other patient was compound heterozygotes for ATM: c.8911C>T and c.7141_7151delAATGGAAAAAT, both of which were not reported previously and not found in 200 control chromosomes. This study widens the spectrum of mutations and phenotypes in ataxia telangiectasia.

Jiang D, Zhang Y, Hart RP, et al.
Alteration in 5-hydroxymethylcytosine-mediated epigenetic regulation leads to Purkinje cell vulnerability in ATM deficiency.
Brain. 2015; 138(Pt 12):3520-36 [PubMed] Article available free on PMC after 01/05/2017 Related Publications
A long-standing mystery surrounding ataxia-telangiectasia is why it is mainly cerebellar neurons, Purkinje cells in particular, that appear vulnerable to ATM deficiency. Here we present data showing that 5-hydroxymethylcytosine (5hmC), a newly recognized epigenetic marker found at high levels in neurons, is substantially reduced in human ataxia-telangiectasia and Atm(-/-) mouse cerebellar Purkinje cells. We further show that TET1, an enzyme that converts 5-methylcytosine (5mC) to 5hmC, responds to DNA damage and manipulation of TET1 activity directly affects the DNA damage signalling and ATM-deficient neuronal cell cycle re-entry and death. Quantitative genome-wide analysis of 5hmC-containing sequences shows that in ATM deficiency there is a cerebellum- and Purkinje cell-specific shift in 5hmC enrichment in both regulatory elements and repeated sequences. Finally, we verify that TET1-mediated 5hmC production is linked to the degenerative process of Purkinje cells and behavioural deficits in Atm(-/-) mice. Taken together, the selective loss of 5hmC plays a critical role in driving Purkinje cell vulnerability in ATM deficiency.

Chen Z, Ye W, Long Z, et al.
Targeted Next-Generation Sequencing Revealed Novel Mutations in Chinese Ataxia Telangiectasia Patients: A Precision Medicine Perspective.
PLoS One. 2015; 10(10):e0139738 [PubMed] Article available free on PMC after 01/05/2017 Related Publications
Ataxia telangiectasia (AT) is an autosomal recessive disease characterized by progressive cerebellar ataxia, oculocutaneous telangiectasia and immunodeficiency due to mutations in the ATM gene. We performed targeted next-generation sequencing (NGS) on three unrelated patients and identified five disease-causing variants in three probands, including two pairs of heterozygous variants (FAT-1:c.4396C>T/p.R1466X, c.1608-2A>G; FAT-2:c.4412_4413insT/p.L1472Ffs*19, c.8824C>T/p.Q2942X) and one pair of homozygous variants (FAT-3: c.8110T>G/p.C2704G, Hom). With regard to precision medicine for rare genetic diseases, targeted NGS currently enables the rapid and cost-effective identification of causative mutations and is an updated molecular diagnostic tool that merits further optimization. This high-throughput data-based strategy would propel the development of precision diagnostic methods and establish a foundation for precision medicine.

Campbell A, Krupp B, Bushman J, et al.
A novel mouse model for ataxia-telangiectasia with a N-terminal mutation displays a behavioral defect and a low incidence of lymphoma but no increased oxidative burden.
Hum Mol Genet. 2015; 24(22):6331-49 [PubMed] Article available free on PMC after 01/05/2017 Related Publications
Ataxia-telangiectasia (A-T) is a rare multi-system disorder caused by mutations in the ATM gene. Significant heterogeneity exists in the underlying genetic mutations and clinical phenotypes. A number of mouse models have been generated that harbor mutations in the distal region of the gene, and a recent study suggests the presence of residual ATM protein in the brain of one such model. These mice recapitulate many of the characteristics of A-T seen in humans, with the notable exception of neurodegeneration. In order to study how an N-terminal mutation affects the disease phenotype, we generated an inducible Atm mutant mouse model (Atm(tm1Mmpl/tm1Mmpl), referred to as A-T [M]) predicted to express only the first 62 amino acids of Atm. Cells derived from A-T [M] mutant mice exhibited reduced cellular proliferation and an altered DNA damage response, but surprisingly, showed no evidence of an oxidative imbalance. Examination of the A-T [M] animals revealed an altered immunophenotype consistent with A-T. In contrast to mice harboring C-terminal Atm mutations that disproportionately develop thymic lymphomas, A-T [M] mice developed lymphoma at a similar rate as human A-T patients. Morphological analyses of A-T [M] cerebella revealed no substantial cellular defects, similar to other models of A-T, although mice display behavioral defects consistent with cerebellar dysfunction. Overall, these results suggest that loss of Atm is not necessarily associated with an oxidized phenotype as has been previously proposed and that loss of ATM protein is not sufficient to induce cerebellar degeneration in mice.

Lohmann E, Krüger S, Hauser AK, et al.
Clinical variability in ataxia-telangiectasia.
J Neurol. 2015; 262(7):1724-7 [PubMed] Related Publications
Ataxia-telangiectasia (A-T) is an autosomal recessive inherited disease characterized by progressive childhood-onset cerebellar ataxia, oculomotor apraxia, choreoathetosis and telangiectasias of the conjunctivae. Further symptoms may be immunodeficiency and frequent infections, and an increased risk of malignancy. As well as this classic manifestation, several other non-classic forms exist, including milder or incomplete A-T phenotypes caused by homozygous or compound heterozygous mutations in the ATM gene. Recently, ATM mutations have been found in 13 Canadian Mennonites with early-onset, isolated, predominantly cervical dystonia, in a French family with generalized dystonia and in an Indian family with dopa-responsive cervical dystonia. In this article, we will describe a Turkish family with three affected sibs. Their phenotypes range from pure cervical dystonia associated with hand tremor to truncal and more generalized dystonic postures. Exome sequencing has revealed the potentially pathogenic compound heterozygous variants p.V2716A and p.G301VfsX19 in the ATM gene. The variants segregated perfectly with the phenotypes within the family. Both mutations detected in ATM have been shown to be pathogenic, and the α-fetoprotein, a marker of ataxia telangiectasia, was found to be increased. This report supports recent literature showing that ATM mutations are not exclusively associated with A-T but may also cause a more, even intra-familial variable phenotype in particular in association with dystonia.

Meschini R, Morucci E, Berni A, et al.
Role of chromatin structure modulation by the histone deacetylase inhibitor trichostatin A on the radio-sensitivity of ataxia telangiectasia.
Mutat Res. 2015; 777:52-9 [PubMed] Related Publications
At present, a lot is known about biochemical aspects of double strand breaks (DBS) repair but how chromatin structure affects this process and the sensitivity of DNA to DSB induction is still an unresolved question. Ataxia telangiectasia (A-T) patients are characterised by very high sensitivity to DSB-inducing agents such as ionising radiation. This radiosensitivity is revealed with an enhancement of chromosomal instability as a consequence of defective DNA repair for a small fraction of breaks located in the heterochromatin, where they are less accessible. Besides, recently it has been reported that Ataxia Telangiectasia Mutated (ATM) mediated signalling modifies chromatin structure. In order to study the impact of chromatin compaction on the chromosomal instability of A-T cells, the response to trichostatin-A, an histone deacetylase inhibitor, in normal and A-T lymphoblastoid cell lines was investigated testing its effect on chromosomal aberrations, cell cycle progression, DNA damage and repair after exposure to X-rays. The results suggest that the response to both trichostatin-A pre- and continuous treatments is independent of the presence of either functional or mutated ATM protein, as the reduction of chromosomal damage was found also in the wild-type cell line. The presence of trichostatin-A before exposure to X-rays could give rise to prompt DNA repair functioning on chromatin structure already in an open conformation. Differently, trichostatin-A post-treatment causing hyperacetylation of histone tails and reducing the heterochromatic DNA content might diminish the requirement for ATM and favour DSBs repair reducing chromosomal damage only in A-T cells. This fact could suggest that trichostatin-A post-treatment is favouring the slow component of DSB repair pathway, the one impaired in absence of a functionally ATM protein. Data obtained suggest a fundamental role of chromatin compaction on chromosomal instability in A-T cells.

Kuranova ML, Pleskach NM, Ledashcheva TA, et al.
[Mosaic forms of ataxia-telangiectasia].
Tsitologiia. 2014; 56(8):619-29 [PubMed] Related Publications
Ataxia-telangiectasia (AT) is a severe hereditary autosomal recessive neurodegenerative disease associated with accelerated aging and caused by mutation in both alleles of atm gene. This gene encodes a key protein of cell response to DNA damage--an ATM protein kinase. Normally, upon formation of DNA double strand breaks ATM is autophosphorylated and its active form phospho-ATM (P-ATM) appears. Here we describe a mosaic form of AT in which cells of the same patient with normal atm gene demonstrated the accumulation of P-ATM in response to DNA double-strand breaks-inducing factors whereas in cells bearing a mutant form of atm P-ATM was not detected. The epigenetic markers such as histone deacetylases SIRT1 and SIRT6, and trimethylated forms of histone H3 - H3K9me3 and H3K27me3--were studied in the nuclei of primary fibroblasts derived from patients with different forms of AT and the increase of SIRT6 level was revealed.

Liu J, Wang X, Ren Y, et al.
Effect of single nucleotide polymorphism Rs189037 in ATM gene on risk of lung cancer in Chinese: a case-control study.
PLoS One. 2014; 9(12):e115845 [PubMed] Article available free on PMC after 01/05/2017 Related Publications
BACKGROUND: Accumulated evidence has indicated that ataxia-telangiectasia mutated (ATM) gene polymorphisms are closely related to lung cancer. We aimed to explore the prognostic value of rs189037 (G>A), one of ATM single nucleotide polymorphisms (SNPs), and detect whether it involves in the risk of lung cancer in Chinese Han people.
METHODS: In this hospital-based matched case-control study, 852 lung cancer patients and 852 healthy controls have been put into comparison to analyze the association between rs189037 and lung cancer risk in Chinese. The single nucleotide polymorphisms were determined by TaqMan real-time PCR and we used SPSS software to perform the statistical analyses.
RESULTS: Individuals carrying variant AA genotype of rs189037 had higher lung cancer risk (adjusted OR: 1.56) than those carrying GG genotype. After analyzing data respectively from different groups divided by genders and smoking status, we observed that the risk effect of AA genotype on the lung cancer was significant in females, non-smokers and female non-smokers, as well as the risk effect of GA genotype in male smokers. Compared with non-smokers carrying GG genotype, smokers carrying at least one A allele had higher risk of developing lung cancer than those with GG genotype (adjusted OR: 3.52 vs. adjusted OR: 2.53).
CONCLUSIONS: This study suggested that rs189037 (G>A) polymorphism is associated with lung cancer risk in Chinese Han population. AA genotype and A allele may be dangerous lung cancer signals in Chinese and make contribution to diagnostic and treatment value.

Kim YJ, Ahn KS, Kim M, et al.
Targeted disruption of Ataxia-telangiectasia mutated gene in miniature pigs by somatic cell nuclear transfer.
Biochem Biophys Res Commun. 2014; 452(4):901-5 [PubMed] Related Publications
Ataxia telangiectasia (A-T) is a recessive autosomal disorder associated with pleiotropic phenotypes, including progressive cerebellar degeneration, gonad atrophy, and growth retardation. Even though A-T is known to be caused by the mutations in the Ataxia telangiectasia mutated (ATM) gene, the correlation between abnormal cellular physiology caused by ATM mutations and the multiple symptoms of A-T disease has not been clearly determined. None of the existing ATM mouse models properly reflects the extent to which neurological degeneration occurs in human. In an attempt to provide a large animal model for A-T, we produced gene-targeted pigs with mutations in the ATM gene by somatic cell nuclear transfer. The disrupted allele in the ATM gene of cloned piglets was confirmed via PCR and Southern blot analysis. The ATM gene-targeted pigs generated in the present study may provide an alternative to the current mouse model for the study of mechanisms underlying A-T disorder and for the development of new therapies.

Gilmore EC
DNA repair abnormalities leading to ataxia: shared neurological phenotypes and risk factors.
Neurogenetics. 2014; 15(4):217-28 [PubMed] Related Publications
Since identification of mutations in the ATM gene leading to ataxia-telangiectasia, enormous efforts have been devoted to discovering the roles this protein plays in DNA repair as well as other cellular functions. Even before the identification of ATM mutations, it was clear that other diseases with different genomic loci had very similar neurological symptoms. There has been significant progress in understanding why cancer and immunodeficiency occur in ataxia-telangiectasia even though many details remain to be determined, but the field is no closer to determining why the nervous system requires ATM and other DNA repair genes. Even though rodent disease models have similar DNA repair abnormalities as the human diseases, they have no consistent, robust neuropathological phenotype making it difficult to understand the neurological underpinnings of disease. Therefore, it may be useful to reassess the neurological and neuropathological characteristics of ataxia-telangiectasia in human patients to look for potential commonalities in DNA repair diseases that result in ataxia. In doing so, it is clear that ataxia-telangiectasia and similar diseases share neurological features other than merely ataxia, such as length-dependent motor and sensory neuropathies, and that the neuroanatomical localization for these symptoms is understood. Cells affected in ataxia-telangiectasia and similar diseases are some of the largest single nucleated cells in the body. In addition, a subset of these diseases also has extrapyramidal movements and oculomotor apraxia. These neurological and neuropathological similarities may indicate a common DNA repair related pathogenesis with very large cell size as a critical risk factor.

Boohaker RJ, Xu B
The versatile functions of ATM kinase.
Biomed J. 2014 Jan-Feb; 37(1):3-9 [PubMed] Article available free on PMC after 01/05/2017 Related Publications
Ataxia-telangiectasia mutated (ATM) kinase, the mutation of which causes the autosomal recessive disease ataxia-telangiectasia, plays an essential role in the maintenance of genome stability. Extensive studies have revealed that activated ATM signals to a massive list of proteins to facilitate cell cycle checkpoints, DNA repair, and many other aspects of physiological responses in the event of DNA double-strand breaks. ATM also plays functional roles beyond the well-characterized DNA damage response (DDR). In this review article, we discuss the recent findings on the molecular mechanisms of ATM in DDR, the mitotic spindle checkpoint, as well as hyperactive ATM signaling in cancer invasion and metastasis.

Hasegawa S, Imai K, Yoshida K, et al.
Whole-exome sequence analysis of ataxia telangiectasia-like phenotype.
J Neurol Sci. 2014; 340(1-2):86-90 [PubMed] Related Publications
A number of diseases exhibit neurodegeneration with/without additional symptoms such as immunodeficiency, increased cancer risk, and microcephalus. Ataxia telangiectasia and Nijmegen breakage syndrome, for example, develop as a result of mutations in genes involved in the DNA damage response. However, such diseases can be difficult to diagnose as they are only rarely encountered by physicians. To overcome this challenge, nine patients with symptoms that resemble those of ataxia telangiectasia, including neurodegeneration, hypogammaglobulinemia, telangiectasia, and/or elevated serum α-fetoprotein, were subjected to whole-exome sequencing (WES) to identify the causative mutations. Molecular diagnosis was achieved in two patients: one displayed CD40 ligand (CD40LG) deficiency, while a second showed a homozygous SIL1 mutation, which has been linked to Marinesco-Sjögren syndrome (MSS). Typical features of CD40LG deficiency and MSS are distinct from the symptoms usually seen in ataxia telangiectasia. These dissociations between phenotype and genotype make it difficult to achieve molecular diagnosis of orphan diseases. Whole-exome sequencing analyses will assist in the molecular diagnosis of such cases and allow the identification of genotypes that would not be expected from the phenotype.

Sharma NK, Lebedeva M, Thomas T, et al.
Intrinsic mitochondrial DNA repair defects in Ataxia Telangiectasia.
DNA Repair (Amst). 2014; 13:22-31 [PubMed] Related Publications
Ataxia Telangiectasia (A-T) is a progressive childhood disorder characterized most notably by cerebellar degeneration and predisposition to cancer. A-T is caused by mutations in the kinase ATM, a master regulator of the DNA double-strand break response. In addition to DNA-damage signaling defects, A-T cells display mitochondrial dysfunction that is thought to contribute to A-T pathogenesis. However, the molecular mechanism leading to mitochondrial dysfunction in A-T remains unclear. Here, we show that lack of ATM leads to reduced mitochondrial DNA (mtDNA) integrity and mitochondrial dysfunction, which are associated to defective mtDNA repair. While protein levels of mtDNA repair proteins are essentially normal, in the absence of ATM levels specifically of DNA ligase III (Lig3), the only DNA ligase working in mitochondria is reduced. The reduction of Lig3 is observed in different A-T patient cells, in brain and pre-B cells derived from ATM knockout mice as well as upon transient or stable knockdown of ATM. Furthermore, pharmacological inhibition of Lig3 in wild type cells phenocopies the mtDNA repair defects observed in A-T patient cells. As targeted deletion of LIG3 in the central nervous system causes debilitating ataxia in mice, reduced Lig3 protein levels and the consequent mtDNA repair defect may contribute to A-T neurodegeneration. A-T is thus the first disease characterized by diminished Lig3.

Li J, Hart RP, Mallimo EM, et al.
EZH2-mediated H3K27 trimethylation mediates neurodegeneration in ataxia-telangiectasia.
Nat Neurosci. 2013; 16(12):1745-53 [PubMed] Article available free on PMC after 01/05/2017 Related Publications
The symptoms of ataxia-telangiectasia (A-T) include a progressive neurodegeneration caused by ATM protein deficiency. We previously found that nuclear accumulation of histone deacetylase-4, HDAC4, contributes to this degeneration; we now report that increased trimethylation of histone H3 on Lys27 (H3K27me3) mediated by polycomb repressive complex 2 (PRC2) is also important in the A-T phenotype. Enhancer of zeste homolog 2 (EZH2), a core catalytic component of PRC2, is a new ATM kinase target, and ATM-mediated phosphorylation of EZH2 on Ser734 reduces protein stability. Thus, PRC2 formation is elevated along with H3K27me3 in ATM deficiency. Chromatin immunoprecipitation and sequencing showed an increase in H3K27me3 'marks' and a dramatic shift in their location. The change of H3K27me3 chromatin-binding pattern is directly related to cell cycle reentry and cell death of ATM-deficient neurons. Lentiviral knockdown of EZH2 rescued Purkinje cell degeneration and behavioral abnormalities in Atm(-/-) mice, demonstrating that EZH2 hyperactivity is another key factor in A-T neurodegeneration.

Davis MY, Keene CD, Swanson PD, et al.
Novel mutations in ataxia telangiectasia and AOA2 associated with prolonged survival.
J Neurol Sci. 2013; 335(1-2):134-8 [PubMed] Article available free on PMC after 01/05/2017 Related Publications
Ataxia telangiectasia (AT) and ataxia oculomotor apraxia type 2 (AOA2) are autosomal recessive ataxias caused by mutations in genes involved in maintaining DNA integrity. Lifespan in AT is greatly shortened (20s-30s) due to increased susceptibility to malignancies (leukemia/lymphoma). Lifespan in AOA2 is uncertain. We describe a woman with variant AT with two novel mutations in ATM (IVS14+2T>G and 5825C>T, p.A1942V) who died at age 48 with pancreatic adenocarcinoma. Her mutations are associated with an unusually long life for AT and with a cancer rarely associated with that disease. We also describe two siblings with AOA2, heterozygous for two novel mutations in senataxin (3 bp deletion c.343-345 and 1398T>G, p.I466M) who have survived into their 70s, allowing us to characterize the longitudinal course of AOA2. In contrast to AT, we show that persons with AOA2 can experience a prolonged lifespan with considerable motor disability.

Zhang L, Simpson DA, Innes CL, et al.
Gene expression signatures but not cell cycle checkpoint functions distinguish AT carriers from normal individuals.
Physiol Genomics. 2013; 45(19):907-16 [PubMed] Article available free on PMC after 01/05/2017 Related Publications
Ataxia telangiectasia (AT) is a rare autosomal recessive disease caused by mutations in the ataxia telangiectasia-mutated gene (ATM). AT carriers with one mutant ATM allele are usually not severely affected although they carry an increased risk of developing cancer. There has not been an easy and reliable diagnostic method to identify AT carriers. Cell cycle checkpoint functions upon ionizing radiation (IR)-induced DNA damage and gene expression signatures were analyzed in the current study to test for differential responses in human lymphoblastoid cell lines with different ATM genotypes. While both dose- and time-dependent G1 and G2 checkpoint functions were highly attenuated in ATM-/- cell lines, these functions were preserved in ATM+/- cell lines equivalent to ATM+/+ cell lines. However, gene expression signatures at both baseline (consisting of 203 probes) and post-IR treatment (consisting of 126 probes) were able to distinguish ATM+/- cell lines from ATM+/+ and ATM-/- cell lines. Gene ontology (GO) and pathway analysis of the genes in the baseline signature indicate that ATM function-related categories, DNA metabolism, cell cycle, cell death control, and the p53 signaling pathway, were overrepresented. The same analyses of the genes in the IR-responsive signature revealed that biological categories including response to DNA damage stimulus, p53 signaling, and cell cycle pathways were overrepresented, which again confirmed involvement of ATM functions. The results indicate that AT carriers who have unaffected G1 and G2 checkpoint functions can be distinguished from normal individuals and AT patients by expression signatures of genes related to ATM functions.

Ludwig LB, Valiati VH, Palazzo RP, et al.
Chromosome instability and oxidative stress markers in patients with ataxia telangiectasia and their parents.
Biomed Res Int. 2013; 2013:762048 [PubMed] Article available free on PMC after 01/05/2017 Related Publications
Ataxia telangiectasia (AT) is a rare neurodegenerative disorder, inherited in an autosomal recessive manner. Total blood samples were collected from 20 patients with AT, 13 parents of patients, and 17 healthy volunteers. This study aimed at evaluating the frequency of chromosomal breaks in spontaneous cultures, induced by bleomycin and ionizing radiation, and further evaluated the rates of oxidative stress in AT patients and in their parents, compared to a control group. Three cell cultures were performed to each individual: the first culture did not receive induction to chromosomal instability, the second was exposed to bleomycin, and the last culture was exposed to ionizing radiation. To evaluate the rates of oxidative stress, the markers superoxide dismutase (SOD), catalase (CAT), and thiobarbituric acid (TBARS) were utilized. Significant differences were observed between the three kinds of culture treatments (spontaneous, bleomycin, and radiation induced) and the breaks and chromosomal aberrations in the different groups. The oxidative stress showed no significant differences between the markers. This study showed that techniques of chromosomal instability after the induction of ionizing radiation and bleomycin are efficient in the identification of syndrome patients, with the ionizing radiation being the most effective.

Regal JA, Festerling TA, Buis JM, Ferguson DO
Disease-associated MRE11 mutants impact ATM/ATR DNA damage signaling by distinct mechanisms.
Hum Mol Genet. 2013; 22(25):5146-59 [PubMed] Article available free on PMC after 01/05/2017 Related Publications
DNA double-strand breaks (DSBs) can lead to instability of the genome if not repaired correctly. The MRE11/RAD50/NBS1 (MRN) complex binds DSBs and initiates damage-induced signaling cascades via activation of the ataxia-telangiectasia mutated (ATM) and ataxia-telangiectasia- and rad3-related (ATR) kinases. Mutations throughout MRE11 cause ataxia-telangiectasia-like disorder (ATLD) featuring cerebellar degeneration, and cancer-predisposition in certain kindreds. Here, we have examined the impact on DNA damage signaling of several disease-associated MRE11A alleles to gain greater understanding of the mechanisms underlying the diverse disease sequelae of ATLD. To this end, we have designed a system whereby endogenous wild-type Mre11a is conditionally deleted and disease-associated MRE11 mutants are stably expressed at physiologic levels. We find that mutations in the highly conserved N-terminal domain impact ATM signaling by perturbing both MRE11 interaction with NBS1 and MRE11 homodimerization. In contrast, an inherited allele in the MRE11 C-terminus maintains MRN interactions and ATM/ATR kinase activation. These findings reveal that ATLD patients have reduced ATM activation resulting from at least two distinct mechanisms: (i) N-terminal mutations destabilize MRN interactions, and (ii) mutation of the extreme C-terminus maintains interactions but leads to low levels of the complex. The N-terminal mutations were found in ATLD patients with childhood cancer; thus, our studies suggest a clinically relevant dichotomy in MRE11A alleles. More broadly, these studies underscore the importance of understanding specific effects of hypomorphic disease-associated mutations to achieve accurate prognosis and appropriate long-term medical surveillance.

Huang Y, Yang L, Wang J, et al.
Twelve novel Atm mutations identified in Chinese ataxia telangiectasia patients.
Neuromolecular Med. 2013; 15(3):536-40 [PubMed] Article available free on PMC after 01/05/2017 Related Publications
Ataxia telangiectasia (A-T) is an autosomal recessive disease characterized mainly by progressive cerebellar ataxia, oculocutaneous telangiectasia, and immunodeficiency. This disease is caused by mutations of the ataxia telangiectasia mutated (Atm) gene. More than 500 Atm mutations that are responsible for A-T have been identified so far. However, there have been very few A-T cases reported in China, and only two Chinese A-T patients have undergone Atm gene analysis. In order to systemically investigate A-T in China and map their Atm mutation spectrum, we recruited eight Chinese A-T patients from six unrelated families nationwide. Using direct sequencing of genomic DNA and the multiplex ligation-dependent probe amplification, we identified twelve pathogenic Atm mutations, including one missense, four nonsense, five frameshift, one splicing, and one large genomic deletion. All the Atm mutations we identified were novel, and no homozygous mutation and founder-effect mutation were found. These results suggest that Atm mutations in Chinese populations are diverse and distinct largely from those in other ethnic areas.

Lavin MF
The appropriateness of the mouse model for ataxia-telangiectasia: neurological defects but no neurodegeneration.
DNA Repair (Amst). 2013; 12(8):612-9 [PubMed] Related Publications
Patients with ataxia-telangiectasia (A-T) are characterised by genome instability, cancer predisposition and a progressive neurodegeneration. A number of model systems have been developed for A-T but none recapitulate all the phenotype. The majority of these models have been generated in mice. While Atm deficient mouse models exhibit much of the phenotype described in patients with A-T, the broad consensus is that they do not display the most debilitating aspect of A-T, i.e. neurodegeneration. Cerebellar atrophy is one of the neuronal characteristics of A-T patients due to defects in neuronal development and progressive loss of Purkinje and granule cells. This is not evident in Atm-deficient mutants but there are multiple reports on neurological abnormalities in these mice. The focus of this review is to evaluate the appropriateness of Atm mutant mouse models for A-T, particularly with reference to neurological abnormalities and how they might relate to neurodegeneration.

Carlessi L, Fusar Poli E, De Filippis L, Delia D
ATM-deficient human neural stem cells as an in vitro model system to study neurodegeneration.
DNA Repair (Amst). 2013; 12(8):605-11 [PubMed] Article available free on PMC after 01/05/2017 Related Publications
Loss of ATM kinase, a transducer of the DNA damage response and redox sensor, causes the neurodegenerative disorder ataxia-telangiectasia (A-T). While a great deal of progress has been made in elucidating the ATM-dependent DNA damage response (DDR) network, a key challenge remains in understanding the selective susceptibility of the nervous system to faulty DDR. Several factors appear implicated in the neurodegenerative phenotype in A-T, but which of them plays a crucial role remains unclear, especially since mouse models of A-T do not fully mirror the respective human syndrome. Therefore, a number of human neural stem cell (hNSC) systems have been developed to get an insight into the molecular mechanisms of neurodegeneration as consequence of ATM inactivation. Here we review the hNSC systems developed by us an others to model A-T.

Huh HJ, Cho KH, Lee JE, et al.
Identification of ATM mutations in Korean siblings with ataxia-telangiectasia.
Ann Lab Med. 2013; 33(3):217-20 [PubMed] Article available free on PMC after 01/05/2017 Related Publications
Ataxia-telangiectasia (A-T) is a rare autosomal recessive neurodegenerative disorder. It is characterized by early-onset, progressive cerebellar ataxia, oculomotor apraxia, choreoathetosis, conjunctival telangiectasias, immunodeficiency, and an increased risk of malignancy. Although A-T is known to be the most common cause of progressive cerebellar ataxia in childhood, there have been no confirmed cases in Korea. We report the clinical and genetic findings of Korean siblings who presented with limb and truncal ataxia, oculomotor apraxia, choreoathetosis, and telangiectasias of the eyes. Sequence analysis of the ataxia-telangiectasia mutated (ATM) gene revealed a known missense mutation (c.8546G>C; p.Arg2849Pro) and a novel intronic variant of intron 17 (c.2639-19_2639-7del13). Reverse-transcription PCR and sequencing analysis revealed that the c.2639-19_2639-7del13 variant causes a splicing aberration that potentiates skipping exon 18. Because A-T is quite rare in Korea, the diagnosis of A-T in Korean patients can be delayed. We recommend that a diagnosis of A-T should be suspected in Korean patients exhibiting the clinical features of A-T.

Claes K, Depuydt J, Taylor AM, et al.
Variant ataxia telangiectasia: clinical and molecular findings and evaluation of radiosensitive phenotypes in a patient and relatives.
Neuromolecular Med. 2013; 15(3):447-57 [PubMed] Related Publications
Variant ataxia telangiectasia (A-T) may be an underdiagnosed entity. We correlate data from radiosensitivity and kinase assays with clinical and molecular data from a patient with variant A-T and relatives. The coding region of ATM was sequenced. To evaluate the functional effect of the mutations, we performed kinase assays and developed a novel S-G2 micronucleus test. Our patient presented with mild dystonia, moderately dysarthric speech, increased serum α-fetoprotein but no ataxia nor telangiectasias, no nystagmus or oculomotor dyspraxia. She has a severe IgA deficiency, but does not have recurrent infections. She is compound heterozygote for ATM c.8122G>A (p.Asp2708Asn) and c.8851-1G>T, leading to in frame loss of 63 nucleotides at the cDNA level. A trace amount of ATM protein is translated from both alleles. Residual kinase activity is derived only from the p.Asp2708Asn allele. The conventional G0 micronucleus test, based on irradiation of resting lymphocytes, revealed a radiosensitive phenotype for the patient, but not for the heterozygous relatives. As ATM is involved in homologous recombination and G2/M cell cycle checkpoint, we optimized an S-G2 micronucleus assay, allowing to evaluate micronuclei in lymphocytes irradiated in the S and G2 phases. This test showed increased radiosensitivity for both the patient and the heterozygous carriers. Intriguingly, heterozygous carriers of c.8851-1G>T (mutation associated with absence of kinase activity) showed a stronger radiosensitive phenotype with this assay than heterozygous carriers of p.Asp2708Asn (mutation associated with residual kinase activity). The modified S-G2 micronucleus assay provided phenotypic insight into complement the diagnosis of this atypical A-T patient.

Bielorai B, Fisher T, Waldman D, et al.
Acute lymphoblastic leukemia in early childhood as the presenting sign of ataxia-telangiectasia variant.
Pediatr Hematol Oncol. 2013; 30(6):574-82 [PubMed] Related Publications
Ataxia-telangiectasia (A-T), an autosomal recessive disorder is characterized by progressive neurodegeneration, immunodeficiency, sensitivity to ionizing radiation, and predisposition to cancer, especially to lymphoid malignancies. A-T variant is characterized by a milder clinical phenotype and is caused by missense or leaky splice site mutations that produce residual ataxia telangiectasia mutated (ATM) kinase activity. Lymphoid malignancy can precede the diagnosis of A-T, particularly in young children with mild neurological symptoms. We studied a consanguineous family with four A-T variant patients, three of them developed T-ALL at a young age before the diagnosis of A-T was established. ATM mutation analysis detected two new missense mutations both within exon 12: c.1514T>C and c.1547T>C. All four patients are homozygous for the two mutations, while their parents are heterozygous for the mutations. ATM protein level was low in all patients and the response to the radiomimetic agent, neocarzinostatin, was reduced. Leukemic presentation in a young age in three members of consanguineous family led to the identification of a new missense mutation in the ATM gene. The diagnosis of A-T or A-T variant should be considered in children with neurological abnormalities who develop T-ALL at a young age.

Ambrose M, Gatti RA
Pathogenesis of ataxia-telangiectasia: the next generation of ATM functions.
Blood. 2013; 121(20):4036-45 [PubMed] Article available free on PMC after 01/05/2017 Related Publications
In 1988, the gene responsible for the autosomal recessive disease ataxia- telangiectasia (A-T) was localized to 11q22.3-23.1. It was eventually cloned in 1995. Many independent laboratories have since demonstrated that in replicating cells, ataxia telangiectasia mutated (ATM) is predominantly a nuclear protein that is involved in the early recognition and response to double-stranded DNA breaks. ATM is a high-molecular-weight PI3K-family kinase. ATM also plays many important cytoplasmic roles where it phosphorylates hundreds of protein substrates that activate and coordinate cell-signaling pathways involved in cell-cycle checkpoints, nuclear localization, gene transcription and expression, the response to oxidative stress, apoptosis, nonsense-mediated decay, and others. Appreciating these roles helps to provide new insights into the diverse clinical phenotypes exhibited by A-T patients-children and adults alike-which include neurodegeneration, high cancer risk, adverse reactions to radiation and chemotherapy, pulmonary failure, immunodeficiency, glucose transporter aberrations, insulin-resistant diabetogenic responses, and distinct chromosomal and chromatin changes. An exciting recent development is the ATM-dependent pathology encountered in mitochondria, leading to inefficient respiration and energy metabolism and the excessive generation of free radicals that themselves create life-threatening DNA lesions that must be repaired within minutes to minimize individual cell losses.

Palmeri S, Rufa A, Pucci B, et al.
Clinical course of two Italian siblings with ataxia-telangiectasia-like disorder.
Cerebellum. 2013; 12(4):596-9 [PubMed] Related Publications
Ataxia-telangiectasia-like disorder (ATLD) due to mutations in the MRE11 gene is a very rare autosomal recessive disease, described so far in only 20 patients. Little is known about the onset of the first symptoms or the clinical course of the disease. The present report contributes to the diagnosis of ATLD and its prognosis at onset. We report 30 years of clinical and ophthalmic observations and the results of quantitative magnetic resonance (MR), MR spectroscopy (proton magnetic resonance spectroscopic imaging) and neuropsychological assessment in the first Italian siblings identified with ATLD. Although the disease had early onset and the clinical picture was initially severe, suggesting ataxia-telangiectasia, neurological impairment, ocular motor apraxia and neuropsychological tests showed very slow deterioration in adult age. The patients developed eye and head motor strategies to compensate ocular motor apraxia. MR measurements and MR spectroscopy disclosed widespread neuronal and axonal involvement. ATLD should be considered in patients with ocular apraxia and ataxia in infancy. The long follow-up provided insights into clinical outcome, with functional neuroimaging studies shedding light on the pathogenetic mechanisms of this rare disease.

Jeddane L, Ailal F, Dubois-d'Enghien C, et al.
Molecular defects in Moroccan patients with ataxia-telangiectasia.
Neuromolecular Med. 2013; 15(2):288-94 [PubMed] Related Publications
Ataxia-telangiectasia (AT) is a rare autosomal recessive disease, affecting neurologic and immune system. Numerous mutations are described in the ATM gene in several populations. However, in Morocco, few data are available concerning this condition. Our main goal is to determine clinical, immunological, and molecular presentation of Moroccan patients with AT. We screened 27 patients, out of 22 unrelated families, for ATM gene mutations. All our patients showed ataxia, ocular telangiectasia, and immunodeficiency, as well as elevated serum alphafetoprotein levels. Mean age at diagnosis was 5.51 years, and consanguinity rate was 81.8 %. Mean age at onset was 2.02 years, and mean time to diagnosis was 3.68 years. We found 14 different mutations in 19 unrelated families, of which 7 were not reported. Our results showed that c.5644C>T mutation was the most common in our series. However, further studies are required to demonstrate a founder effects on ATM gene in Moroccan patients, who showed mutational heterogeneity otherwise. Our data indicate that direct sequencing of coding exons is sufficient for a high detection rate in ATM in Moroccan population.

Kuranova ML, Ledashcheva TA, Tulush EK, et al.
[Diagnostics of ataxia-telangiectasia by the express-test found on the method of indirect immunofluorescence].
Tsitologiia. 2013; 55(8):560-5 [PubMed] Related Publications
Ataxia-telangiectasia (AT) is a hereditary severe neurodegenerative disease developing, when mutations take place in both alleles of the atm gene, which encodes the key protein of the cellular response to DNA damage (DDR)--ATM proteinkinase. In response to the occurrence of double-strand DNA breaks, the ATM proteinkinase pass the autophosphorylation, and its active form--the phospho-ATM (P-ATM) appears in cells. In the nuclei of cells having the atm gene, P-ATM is revealed, being absent in cells with mutated forms of this gene, by means of the application of the modified method of indirect immunofluorescence. This peculiarity may be applied in the clinic, in order to confirm the diagnosis of AT.

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