BACKGROUND:

Ataxia telangiectasia (A-T) is a rare disorder with many distinctive neurologic features. Although there is substantial individual variation in the rate of progression of these features, their relationship to one another or to age has not been characterized.

METHODS:

We formulated and tested multiple elements that assess different neurologic functions known to be affected by A-T. The overall index was applied to 52 patients with A-T, 2 to 29 years of age.

RESULTS:

Seven elements items proved to be informative, and three elements were added based on face validity. In a linear regression model of individuals under 19 years of age, controlled for correlation within sibships, age accounted for 87% of the variation in the A-T Index.

CONCLUSION:

Despite substantial individual variability of the phenotypic elements of A-T, scores on this multidimensional index have a very high correlation with age, indicating that there is a characteristic rate of progression of the disease, although functional domains in the brain are differentially affected. The pattern of scores suggests that a severe and a mild form of A-T may be distinguished by this quantitative measure. With further development this index may become useful as an outcome measure for treatment studies and prognosis.

OBJECTIVES:

To determine whether patients with ataxia-telangiectasia exhibit oropharyngeal dysphagia with concomitant aspiration and to examine the relationships among swallowing function, age, and nutritional status.

STUDY DESIGN:

Seventy patients (mean age, 10.7 years; range, 1.8 to 30 years) had feeding/swallowing and nutritional evaluations. Fifty-one patients, in whom there were concerns about swallowing safety, were examined with a standardized videofluoroscopic swallow study.

RESULTS:

Fourteen of the 51 patients (27%) with histories suggestive of dysphagia demonstrated aspiration. Of these, silent aspiration (aspiration without a cough) occurred in 10 (71%) patients. Aspirators were significantly older than non-aspirators (mean age, 16.9 vs 10.8 years; P =.002). Advancing age was the strongest factor associated with aspiration during continuous drinking (P =.01). In patients with ataxia-telangiectasia, weight and weight/height were abnormally low at all ages and most compromised in older patients. Patients who aspirated had significantly lower mean weight (P <.002) and weight/height z scores (P <.001) than did patients who did not aspirate.

CONCLUSIONS:

Oropharyngeal dysphagia is common and appears to be progressive in patients with ataxia-telangiectasia. Older patients also have a higher incidence of poorer nutritional status. The relationship between dysphagia and nutritional status deserves further investigation.

Although abnormal eye movements are a prominent feature of ataxia telangiectasia, the characteristics of the oculomotor dysfunction in the disease have been reported only in small groups of patients. We have examined eye movements clinically in 56 patients with ataxia telangiectasia, and obtained electrooculographic recordings of eye movements in 33 subjects. Deficits were observed in the eye movement systems that stabilize images on the retina, including pursuit, gaze holding, convergence, vestibular and optokinetic slow phases, and cancellation of vestibular slow phases. Abnormalities in the systems that maintain fixation and shift gaze were also prominent, including abnormal reflexive and voluntary saccades (characterized by prolonged latency, hypometric amplitude, and the use of head movements to initiate gaze shifts), impaired fixation, and a reduction in vestibular and optokinetic quick phases. The abnormalities in image stabilization most likely result from dysfunction in the cerebellar flocculus and paraflocculus. The basis of the saccadic and fixation disturbance is less certain but may be the result of abnormal supranuclear control of the superior colliculus resulting from dysfunction in the cerebellar vermis or the basal ganglia.

The cloning of ATM in 1995, the gene responsible for ataxia-telangiectasia, opened a dimension of biological research that is as complex and intriguing to cell biologists as this classic disorder has been to clinicians for four decades. The phenotype is both variable and stereotyped, with significant differences between patients in the rate of progression or appearance of the multiple features yet consistent in their characteristic nature. Ataxia telangiectasia usually has been misdiagnosed for the first few years of life, while accurate diagnosis might most impact family planning. Newly produced ATM-deficient transgenic mice express most of the cellular features of the disorder but have yet to mimic the distinctive neurodegeneration.

OBJECTIVES:

Ataxia-telangiectasia (AT) is a rare, autosomal recessive neurodegenerative disorder in which the diagnosis is obvious when ataxia and telangiectasia are both present. However, the diagnosis can be made upon the onset of ataxia and before the appearance of telangiectasia if confirmed by laboratory tests. Early diagnosis is important for genetic counseling, appropriate care, and avoidance of unnecessary tests. The purpose of this study is to identify factors responsible for delays in the diagnosis of AT.

DESIGN:

The records of all patients seen at the Ataxia-Telangiectasia Clinical Center from July 1, 1995 to April 1, 1997 were reviewed to determine age of onset of gait abnormality, recognition of telangiectasia, and diagnosis.

RESULTS:

In 48 patients with AT, who were the index cases in their respective families, the median age of diagnosis (78 months) occurred after the onset of gait abnormalities (15 months) and closely corresponded to the development of telangiectasia (72 months). In the majority of cases (34/48), telangiectasia appeared before the diagnosis was established. The most common misdiagnosis was cerebral palsy (29/48 cases). Twenty-one children (4 with AT) were born after the start of symptoms in the index case, but before the establishment of a diagnosis.

CONCLUSIONS:

The term AT, although a concise and memorable label for the disorder, is also a barrier to early diagnosis. We recommend the use of routine serum alpha-fetoprotein testing for all children with persistent ataxia.

The rare human genetic disorder ataxia-telangiectasia (A-T) has multiple consequences including a variable degree of immunodeficiency. Khanna and co-workers (Khanna, K. K., Yan, J., Watters, D., Hobson, K., Beamish, H., Spring, K., Shiloh, Y., Gatti, R. A., and Lavin, M. F. (1997) J. Biol. Chem. 272, 9489-9495) evaluated signaling in Epstein-Barr virus (EBV) immortalized A-T lymphoblastoid cell lines (LCLs), derived from the B cells of A-T patients. They showed that A-T lymphoblastoid cells lack signaling through the B cell antigen receptor and concluded that the fault in A-T encompasses intracellular signaling in B cells. However, it is established that EBV latent membrane protein 2A (LMP2A) blocks signaling in EBV-bearing cells by interaction with cellular tyrosine kinases. To test whether the reported fault in A-T B cells was not inherent in A-T but the result of influence of wild-type EBV, we derived A-T LCLs with wild-type or LMP2A-deleted EBV and studied signaling in these cells in response to cross-linking the B cell antigen receptor. We report that intracellular calcium mobilization and tyrosine phosphorylation in LMP2A-depleted LCLs derived from A-T patients is indistinguishable from that in LMP2A-depleted LCLs derived from normal controls. Further, signaling is blocked similarly in A-T and normal lymphoblastoid cells bearing wild-type EBV. In conclusion there is no evidence of any defect in B cell receptor signal transduction in A-T B cells.

We investigated the presence of hypergammaglobulinemia and oligo-/monoclonal gammopathy in 90 patients (from 80 families) with ataxia-telangiectasia ranging in age from 2 to 29 years. Of the 90 patients, 38.8% displayed hypergammaglobulinemia. An isolated increase in IgM was the most common finding (23.3%) followed by a simultaneous increase in IgM and IgG (8.8%), an isolated increase in IgA (3.3%), an elevated level of IgG (2.2%) and a concomitant increase in IgM and IgA (1.1%), respectively. Seven of the patients (8.1%) had oligo-/monoclonal gammopathy. The gammopathies included all major immunoglobulin isotypes. Chemotherapeutic intervention in 2 cases precipitated the emergence of new clones within a matter of weeks. Further investigation of oligo-/monoclonal gammopathies in these patients may lead to a clearer understanding of the clinical course and provide further insight into the underlying mechanisms of B-cell abnormalities in ataxia-telangiectasia.

Ataxia telangiectasia (A-T) is an autosomal recessive multisystem disorder associated with a variable immune deficiency. The mechanism for this remains unclear. Qualitative and quantitative defects of cellular immunity have been previously reported. However, despite laboratory evidence of significant immune abnormalities, opportunistic infections are uncommon. To address this discrepancy, we analyzed cytokine production by quantitative real-time PCR and T cell function at the single cell level by flow cytometry in four A-T patients. CD4 and CD8 T cell subsets from these patients displayed intact signaling in response to anti-CD3 stimulation, similar to controls. Stimulated T cells from A-T patients also produced normal to increased levels of Th1 (IL-2, IFN-gamma) and Th2 (IL-10, IL-4) cytokines, relative to control values. Our results suggest that T cells from A-T patients may be more functionally intact than previously observed. This helps to explain the paucity of opportunistic infections encountered, unlike that encountered in other primary immunodeficiencies.

Ataxia-telangiectasia (A-T) is an early onset autosomal recessive ataxia associated with characteristic chromosomal aberrations, cell cycle checkpoint defects, cancer susceptibility, and sensitivity to ionizing radiation. We utilized the protein truncation test (PTT), and single strand conformation polymorphism (SSCP) on cDNA, as well as denaturing high performance liquid chromatography (dHPLC) on genomic DNA (gDNA) to screen for mutations in 24 Polish A-T families. Twenty-six distinct Short Tandem Repeat (STR) haplotypes were identified. Three founder mutations accounted for 58% of the alleles. Three-quarters of the families had at least one recurring (shared) mutation, which was somewhat surprising given the low frequency of consanguinity in Poland. STR haplotyping greatly improved the efficiency of mutation detection. We identified 44 of the expected 48 mutations (92%): sixty-nine percent were nonsense mutations, 23% caused aberrant splicing, and 5% were missense mutations. Four mutations have not been previously described. Two of the Polish mutations have been observed previously in Amish and Mennonite A-T patients; this is compatible with historical records. Shared mutations shared the same Single Nucleotide Polymorphism (SNP) and STR haplotypes, indicating common ancestries. The Mennonite mutation, 5932 G>T, is common in Russian A-T families, and the STR haplovariants are the same in both Poland and Russia. Attempts to correlate phenotypes with genotypes were inconclusive due to the limited numbers of patients with identical mutations.

Human genomic instability syndromes affect the nervous system to different degrees of severity, attesting to the vulnerability of the CNS to perturbations of genomic integrity and the DNA damage response (DDR). Ataxia-telangiectasia (A-T) is a typical genomic instability syndrome whose major characteristic is progressive neuronal degeneration but is also associated with immunodeficiency, cancer predisposition and acute sensitivity to ionizing radiation and radiomimetic chemicals. A-T is caused by loss or inactivation of the ATM protein kinase, which mobilizes the complex, multi-branched cellular response to double strand breaks in the DNA by phosphorylating numerous DDR players. The link between ATM's function in the DDR and the neuronal demise in A-T has been questioned in the past. However, recent studies of the ATM-mediated DDR in neurons suggest that the neurological phenotype in A-T is indeed caused by deficiency in this function, similar to other features of the disease. Still, major issues concerning this phenotype remain open, including the presumed differences between the DDR in post-mitotic neurons and proliferating cells, the nature of the damage that accumulates in the DNA of ATM-deficient neurons under normal life conditions, the mode of death of ATM-deficient neurons, and the lack of a major neuronal phenotype in the mouse model of A-T. A-T remains a prototype disease for the study of the DDR's role in CNS development and maintenance.

Evidence suggests that astrocytes play key roles in structural and functional organization of neuronal circuits. To understand how astrocytes influence the physiopathology of cerebellar circuits, we cultured cells from cerebella of mice that lack the ATM gene. Mutations in ATM are causative of the human cerebellar degenerative disease ataxia-telangiectasia. Cerebellar cultures grown from Atm^-/- mice had disrupted network synchronization, atrophied astrocytic arborizations, reduced autophagy levels, and higher numbers of synapses per neuron than wild-type cultures. Chimeric circuitries composed of wild-type astrocytes and Atm^-/- neurons were indistinguishable from wild-type cultures. Adult cerebellar characterizations confirmed disrupted astrocyte morphology, increased GABAergic synaptic markers, and reduced autophagy in Atm^-/- compared with wild-type mice. These results indicate that astrocytes can impact neuronal circuits at levels ranging from synaptic expression to global dynamics.

The genome instability syndrome, ataxia-telangiectasia (A-T) is caused by null mutations in the ATM gene, that lead to complete loss or inactivation of the gene's product, the ATM protein kinase. ATM is the primary mobilizer of the cellular response to DNA double-strand breaks (DSBs) - a broad signaling network in which many components are ATM targets. The major clinical feature of A-T is cerebellar atrophy, characterized by relentless loss of Purkinje and granule cells. In Atm-knockout (Atm-KO) mice, complete loss of Atm leads to a very mild neurological phenotype, suggesting that Atm loss is not sufficient to markedly abrogate cerebellar structure and function in this organism. Expression of inactive ("kinase-dead") Atm (Atm^KD) in mice leads to embryonic lethality, raising the question of whether conditional expression of Atm^KD in the murine nervous system would lead to a more pronounced neurological phenotype than Atm loss. We generated two mouse strains in which Atm^KD was conditionally expressed as the sole Atm species: one in the CNS and one specifically in Purkinje cells. Focusing our analysis on Purkinje cells, the dynamics of DSB readouts indicated that DSB repair was delayed longer in the presence of Atm^KD compared to Atm loss. However, both strains exhibited normal life span and displayed no gross cerebellar histological abnormalities or significant neurological phenotype. We conclude that the presence of Atm^KD is indeed more harmful to DSB repair than Atm loss, but the murine central nervous system can reasonably tolerate the extent of this DSB repair impairment. Greater pressure needs to be exerted on genome stability to obtain a mouse model that recapitulates the severe A-T neurological phenotype.

Seventy individuals with ataxia telangiectasia were studied: 29 females and 41 males with an age range of 2 to 42 years. The majority (43/68) presented by 3 years of age with truncal ataxia. All had progressive, handicapping neurological symptoms exhibiting ataxia (70/70), ocular motor apraxia (70/70), an impassive face (70/70), dysarthria (70/70), chorea (68/70), dystonia (55/70) and peripheral neuropathy (50/70). Clinical immune deficiency was present in 43 of 70 patients. Ocular telangiectasia were seen in all but one case and excessive thinness in 54 of 70. The mean age of loss of walking was 10 years and of writing 8 years. All 60 tested showed increased sensitivity to ionizing irradiation, 43 of 48 had an elevated alpha-fetoprotein level and 14 of 21 had an immunoglobulin deficiency. Although there was a marked variation in disease findings sibs were always similar. The heterogeneity seen seems at odds with the unilocus linkage of ataxia telangiectasia to 11q23.

The immunodeficiency in ataxia-telangiectasia (A-T) is highly variable. Laboratory abnormalities correlate poorly with susceptibility to infection and are almost exclusively restricted to patients with mutations resulting in no A-T mutated kinase activity. Opportunistic infections are unusual but sinopulmonary infections are common and can contribute to the development of pulmonary insufficiency. Preventing lung diseaseinvolves maximizing immunity, as well as measures to counteract the tendency to develop pulmonary aspiration, which increases with age. Immunizations should include pneumococcal conjugate, influenza and, in all but the most severely lymphopenic, measles, mumps, rubella, and varicella zoster vaccines. Prophylactic azithromycin is commonly used and believed to be useful, although a firm evidence base for its use in A-T is lacking. Approximately 12-15% of patients require regular immunoglobulin therapy. Further studies are required on potential disease-modulating therapies, such as antioxidants and corticosteroids. Strategies for the modulation of gene transcription remain at the preclinical laboratory stage.

BACKGROUND:

Immunodeficiency in ataxia telangiectasia (A-T) is less severe in patients expressing some mutant or normal ATM kinaseactivity. We, therefore, determined whether expression of residual ATM kinase activity also protected against tumour development in A-T.

METHODS:

From a total of 296 consecutive genetically confirmed A-T patients from the British Isles and the Netherlands, we identified 66 patients who developed a malignant tumour; 47 lymphoid tumours and 19 non-lymphoid tumours were diagnosed. We determined their ATMmutations, and whether cells from these patients expressed any ATM with residual ATM kinase activity.

RESULTS:

In childhood, total absence of ATM kinase activity was associated, almost exclusively, with development of lymphoid tumours. There was an overwhelming preponderance of tumours in patients <16 years without kinase activity compared with those with some residualactivity, consistent with a substantial protective effect of residual ATM kinase activity against tumour development in childhood. In addition, the presence of eight breast cancers in A-T patients, a 30-fold increased risk, establishes breast cancer as part of the A-T phenotype.

CONCLUSION:

Overall, a spectrum of tumour types is associated with A-T, consistent with involvement of ATM in different mechanisms of tumour formation. Tumour type was influenced by ATM allelic heterogeneity, residual ATM kinase activity and age.

The pleiotropic nature of the clinical phenotypes of patients with ataxia-telangiectasia (A-T)--which encompass cerebellar degeneration (leading to ataxia), gonadal atrophy, and cancer predisposition--suggests multiple functions of the gene responsible for the disease. The ataxia-telangiectasia mutated gene product (ATM), whose loss of function is responsible for ataxia-telangiectasia, is a protein kinase that interacts with several substrates and is implicated in mitogenic signal transduction, chromosome condensation, meiotic recombination, cell-cycle control and telomere maintenance. This review focuses on the critical roles that ATM appears to play in cell-cycle checkpoints, DNA repair, telomere metabolism and oxidative stress, indicating how defects in these processes might lead to ataxia-telangiectasia.

Much progress has been made in the early diagnosis of ataxia-telangiectasia since the gene was cloned in 1995, A clinical diagnosis can now be confirmed by radiosensitivity testing (colony survival assay), immunoblotting, and mutation detection. The diagnostic value of serum alpha-fetoprotein levels and radiosensitivity has been reevaluated using patients with diagnoses based on the presence of mutations in the ATM gene and the absence of ATM protein in nuclear extracts. Little progress has been made in treating the progressive ataxia.

Ataxia-Telangiectasia (A-T) is a genetic condition leading to neurological defects and immune deficiency. The nature of the immune deficiency is highly variable, and in some cases causes significant morbidity and mortality due to recurrent sinopulmonary infections. Although the neurological defects in A-T are progressive, the natural history of the immune deficiency in A-T has not been evaluated formally. In this study we analyse the clinical history and immunological data in 44 patients with A-T who attended the National Ataxia-Telangiectasiaclinic in Nottingham between 2001 and 2011. Using patient medical records and Nottingham University Hospitals (NUH) National Health Service Trust medical IT systems, data regarding clinical history, use of immunoglobulin replacement therapy, total immunoglobulin levels, specific antibody levels and lymphocyte subset counts were obtained. T cell receptor spectratyping results in some patients were already available and, where possible, repeat blood samples were collected for analysis. This study shows that subtle quantitative changes in certain immunological parameters such as lymphocyte subset counts may occur in patients with A-T over time. However, in general, for the majority of patients the severity of immune deficiency (both clinically and in terms of immunological blood markers) does not seem to deteriorate significantly with time. This finding serves to inform the long-term management of this cohort of patients because, if recurrent respiratory tract infections present later in life, then other contributory factors (e.g. cough/swallowing difficulties, underlying lung disease) should be investigated aggressively. Our findings also offer some form of reassurance for parents of children with A-T, which is otherwise a progressively severely debilitating condition.