Immunodeficiency and infections in ataxia-telangiectasia

Primary immunodeficiency diseases associated with neurologic manifestations

Primary immunodeficiency diseases (PID) are a heterogeneous group of inherited disorders of the immune system, predisposing individuals to recurrent infections, allergy, autoimmunity, and malignancies. A considerable number of these conditions have been found to be also associated with neurologic signs and symptoms. These manifestations are considered core features of some immunodeficiency syndromes, such as ataxia-telangiectasia and purine nucleoside phosphorylase deficiency, or occur less prominently in some others. Diverse pathological mechanisms including defective responses to DNA damage, metabolic errors, and autoimmune phenomena have been associated with neurologic abnormalities; however, several issues remain to be elucidated. Greater awareness of these associated features and gaining a better understanding of the contributing mechanisms will lead to prompt diagnosis and treatment and possibly development of novel preventive and therapeutic strategies. In this review, we aim to provide a brief description of the clinical and genetic characteristics of PID associated with neurologic complications.

ATM and the molecular pathogenesis of ataxia telangiectasia

Ataxia telangiectasia (A-T) results from inactivation of the ATM protein kinase. DNA-damage signaling is a prime function of this kinase, although other roles have been ascribed to ATM. Identifying the primary ATM function(s) for tissue homeostasis is key to understanding how these functions contribute to the prevention of A-T-related pathology. In this regard, because A-T is primarily a neurodegenerative disease, it is essential to understand how ATM loss results in degenerative effects on the nervous system. In addition to delineating the biochemistry and cell biology of ATM, important insights into the molecular basis for neurodegeneration in A-T come from a spectrum of phenotypically related neurodegenerative diseases that directly result from DNA-repair deficiency. Together with A-T, these syndromes indicate that neurodegeneration can be caused by the failure to appropriately respond to DNA damage. This review focuses on defective DNA-damage signaling as the underlying cause of A-T.

Immunodeficiency in Vici syndrome: a heterogeneous phenotype

Vici syndrome is a rare congenital multisystem disorder characterized by agenesis of the corpus callosum, hypotonia, developmental delay, hypopigmentation, cataract, cardiomyopathy, and immunological abnormalities. Recurrent infections, mainly affecting the respiratory tract, have been reported in the majority of cases, representing an important risk factor for morbidity and mortality. The immunological phenotype of patients is extremely variable, ranging from a combined immunodeficiency to nearly normal immunity. We report on a new patient with Vici syndrome, in whom we have extensively investigated immunological features. Despite a mild impairment of the cellular compartment, a defect of humoral immunity was found, requiring treatment with intravenous immunoglobulin. A wider knowledge of immune system abnormalities of Vici syndrome will help to plan strategies for treatment and prevention of infections, such as immunoglobulin replacement and antimicrobial prophylaxis, resulting in improved survival rates.

DNA repair deficiency in neurodegeneration

Deficiency in repair of nuclear and mitochondrial DNA damage has been linked to several neurodegenerative disorders. Many recent experimental results indicate that the post-mitotic neurons are particularly prone to accumulation of unrepaired DNA lesions potentially leading to progressive neurodegeneration. Nucleotide excision repair is the cellular pathway responsible for removing helix-distorting DNA damage and deficiency in such repair is found in a number of diseases with neurodegenerative phenotypes, including Xeroderma Pigmentosum and Cockayne syndrome. The main pathway for repairing oxidative base lesions is base excision repair, and such repair is crucial for neurons given their high rates of oxygen metabolism. Mismatch repair corrects base mispairs generated during replication and evidence indicates that oxidative DNA damage can cause this pathway to expand trinucleotide repeats, thereby causing Huntington's disease. Single-strand breaks are common DNA lesions and are associated with the neurodegenerative diseases, ataxia-oculomotor apraxia-1 and spinocerebellar ataxia with axonal neuropathy-1. DNA double-strand breaks are toxic lesions and two main pathways exist for their repair: homologous recombination and non-homologous end-joining. Ataxia telangiectasia and related disorders with defects in these pathways illustrate that such defects can lead to early childhood neurodegeneration. Aging is a risk factor for neurodegeneration and accumulation of oxidative mitochondrial DNA damage may be linked with the age-associated neurodegenerative disorders Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis. Mutation in the WRN protein leads to the premature aging disease Werner syndrome, a disorder that features neurodegeneration. In this article we review the evidence linking deficiencies in the DNA repair pathways with neurodegeneration.

Abnormalities in DNA double-strand break response beyond primary immunodeficiency

V(D)J recombination and class switch recombination are achieved by the cooperative processes of recombination activation gene- or activation-induced cytidine deaminase-dependent DNA cleaving, DNA double-strand break (DSB) response signaling, and DNA repair. Primary immunodeficiency due to dysfunctional DNA recombination can be categorized as severe combined immunodeficiency or other conditions, based on the presence or absence of T cells. We can also classify these diseases as radiosensitive or non-radiosensitive immunodeficiencies. While diseases unable to trigger DNA cleavage do not exhibit radiosensitivity, dysfunction in DSB response signaling or repair does lead to radiosensitive immunodeficiency. Recent studies have begun to clarify the mechanisms underlying the molecular pathogenesis of such DNA DSB-related primary immunodeficiency.

Premature ageing of the immune system underlies immunodeficiency in ataxia telangiectasia

ATM kinase modulates pathways implicated in premature ageing and ATM genotype predicts survival, yet immunodeficiency in ataxia telangiectasia is regarded as mild and unrelated to age. We address this paradox in a molecularly characterised sequential adult cohort with classical and mild variant ataxia telangiectasia. Immunodeficiency has the characteristics of premature ageing across multiple cellular and molecular immune parameters. This immune ageing occurs without previous CMV infection. Age predicts immunodeficiency in genetically homogeneous ataxia telangiectasia, and in comparison with controls, calendar age is exceeded by immunological age defined by thymic naïve CD4+ T cell levels. Applying ataxia telangiectasia as a model of immune ageing, pneumococcal vaccine responses, characteristically deficient in physiological ageing, are predicted by thymic naïve CD4+ T cell levels. These data suggest inherited defects of DNA repair may provide valuable insight into physiological ageing. Thymic naïve CD4+ T cells may provide a biomarker for vaccine responsiveness in elderly cohorts.

Educational paper: syndromic forms of primary immunodeficiency

The syndromic primary immunodeficiencies are disorders in which not only the immune system but also other organ systems are affected. Other features most commonly involve the ectodermal, skeletal, nervous, and gastrointestinal systems. Key in identifying syndromic immunodeficiencies is the awareness that increased susceptibility to infections or immune dysregulation in a patient known to have other symptoms or special features may hint at an underlying genetic syndrome. Because the extraimmune clinical features can be highly variable, it is more difficult establishing the correct diagnosis. Nevertheless, correct diagnosis at an early age is important because of the possible treatment options. Therefore, diagnostic work-up is best performed in a center with extensive expertise in this field, having immunologists and clinical geneticists, as well as adequate support from a specialized laboratory at hand. This paper provides the general pediatrician with the main clinical features that are crucial for the recognition of these syndromes.

AID-induced genotoxic stress promotes B cell differentiation in the germinal center via ATM and LKB1 signaling

During an immune response, B cells undergo rapid proliferation and activation-induced cytidine deaminase (AID)-dependent remodeling of immunoglobulin (IG) genes within germinal centers (GCs) to generate memory B and plasma cells. Unfortunately, the genotoxic stress associated with the GC reaction also promotes most B cell malignancies. Here, we report that exogenous and intrinsic AID-induced DNA strand breaks activate ATM, which signals through an LKB1 intermediate to inactivate CRTC2, a transcriptional coactivator of CREB. Using genome-wide location analysis, we determined that CRTC2 inactivation unexpectedly represses a genetic program that controls GC B cell proliferation, self-renewal, and differentiation while opposing lymphomagenesis. Inhibition of this pathway results in increased GC B cell proliferation, reduced antibody secretion, and impaired terminal differentiation. Multiple distinct pathway disruptions were also identified in human GC B cell lymphoma patient samples. Combined, our data show that CRTC2 inactivation, via physiologic DNA damage response signaling, promotes B cell differentiation in response to genotoxic stress.

Evaluation and management of pulmonary disease in ataxia-telangiectasia

Ataxia-telangiectasia (A-T) is a rare autosomal recessive disorder caused by mutations in the ATM gene, resulting in faulty repair of breakages in double-stranded DNA. The clinical phenotype is complex and is characterized by neurologic abnormalities, immunodeficiencies, susceptibility to malignancies, recurrent sinopulmonary infections, and cutaneous abnormalities. Lung disease is common in patients with A-T and often progresses with age and neurological decline. Diseases of the respiratory system cause significant morbidity and are a frequent cause of death in the A-T population. Lung disease in this population is thought to exhibit features of one or more of the following phenotypes: recurrent sinopulmonary infections with bronchiectasis, interstitial lung disease, and lung disease associated with neurological abnormalities. Here, we review available evidence and present expert opinion on the diagnosis, evaluation, and management of lung disease in A-T, as discussed in a recent multidisciplinary workshop. Although more data are emerging on this unique population, many recommendations are made based on similarities to other more well-studied diseases. Gaps in current knowledge and areas for future research in the field of pulmonary disease in A-T are also outlined.

Children with frequent infections: a proposal for a stepwise assessment and investigation of the immune system

Although many children develop frequent infections, only a few have an underlying immune disorder. Children with dysfunction of the immune system develop frequent infections and/or recurrent, persistent, severe, and rare infections. The aim of this review is to provide to the clinician a valuable tool for recognizing any 'discords' of the 'immune-system symphonic orchestra'. By following a reverse route, it will be possible to brighten up the dark and winding road of immunodeficiencies and identify the exact point of immune dysfunction. This is fundamental and crucial to perceive etiologic management and subsequently achieve the best for these young patients and their families.

Genetic determinants at the interface of cancer and neurodegenerative disease

It has been hypothesized that oncogenesis and neurodegeneration may share common mechanistic foundations. Recent evidence now reveals a number of genes in which alteration leads to either carcinogenesis or neurodegeneration, depending on cellular context. Pathways that have emerged as having critical roles in both cancer and neurodegenerative disease include those involving genes such as PARK2, ATM, PTEN, PTPRD, and mTOR. A number of mechanisms have been implicated, and commonly affected cellular processes include cell cycle regulation, DNA repair, and response to oxidative stress. For example, we have recently shown that the E3 ubiquitin ligase PARK2 is mutated or deleted in many different human malignancies and helps drive loss on chromosome 6q25.2-27, a genomic region frequently deleted in cancers. Mutation in PARK2 is also the most common cause of juvenile Parkinson's disease. Mutations in PARK2 result in an upregulation of its substrate cyclin E, resulting in dysregulated entry into the cell cycle. In neurons, this process results in cell death, but in cycling cells, the result is a growth advantage. Thus, depending on whether the cell affected is a dividing cell or a post-mitotic neuron, responses to these alterations may differ, ultimately leading to varying disease phenotypes. Here, we review the substantial data implicating specific genes in both cancer and neurodegenerative disease.

Inherited cancer syndromes in children and young adults

Geneticists estimate that 5% to 10% of all cancers diagnosed in the pediatric age range occur in children born with a genetic mutation that directly increases their lifetime risk for neoplasia. However, despite the fact that only a fraction of cancers in children occur as a result of an identified inherited predisposition, characterizing genetic mutations responsible for increased cancer risk in such syndromes has resulted in a profound understanding of relevant molecular pathways involved in carcinogenesis and/or resistance to neoplasia. Importantly, because most cancer predisposition syndromes result in an increased risk of a small number of defined malignancies, personalized prophylactic surveillance and preventive measures can be implemented in affected patients. Lastly, many of the same genetic targets identified from cancer-prone families are mechanistically involved in the majority of sporadic cancers in adults and children, thereby underscoring the clinical relevance of knowledge gained from these defined syndromes and introducing novel therapeutic opportunities to the broader oncologic community. This review highlights the clinical and genetic features of many of the known constitutional genetic syndromes that predispose to malignancy in children and young adults.

Reversible airway obstruction in children with ataxia telangiectasia

INTRODUCTION

Lung disease is a significant cause of the short life span of ataxia telangiectasia (A-T) patients. Objective lung function measurements are difficult to achieve in A-T.

AIM

To assess lung function by spirometry in relation to the clinical characteristics of A-T patients followed up at the Israeli Ataxia Telangiectasia National Clinic.

PATIENTS AND METHODS

Medical and spirometry data were collected from 27 A-T patients during 2004-2007. Laboratory, nutritional condition, mode of treatment, pulmonary status, and malignancies were assessed. The spirometry values FVC, FEV(1), FEV(0.5), FEF(25-75), PEF and time rise to peak flow were analyzed individually and values were compared to those of healthy age-matched children.

RESULTS

Eleven patients (40.7%) were found to suffer from asthma according to clinical symptoms and response to bronchodilators. We found significant reduction in FEV(1) and FEV(0.5) (z-scores: -0.84 + or - 0.7 SD, -0.7 + or - 0.6 SD; P = 0.0014 and P = 0.003, respectively), in relation to healthy predicted values. FEF(25-75) was significantly lower than that in healthy children in 5 of 11 asthmatic patients. All 27 patients showed higher than healthy FEV(1)/FVC and FEV(0.5)/FVC ratios (z-scores 0.68 + or - 0.99 SD, P < 0.0015, and 2.12 + or - 1.50 SD, P < 0.0015, respectively). The rise time to peak flow was three-fold longer than that of healthy children.

CONCLUSION

Obstructive lung disease is common among A-T patients. Maximal peak flow reduction and prolonged rise time to peak flow may be the first signs of pulmonary involvement in these patients. Early treatment with anti-asthma therapy, bronchodilators, and steroids, may prevent further pulmonary deterioration and improve the prognosis of A-T patients.

Idiopathic thrombocytopenic purpura in a boy with ataxia telangiectasia on immunoglobulin replacement therapy

Ataxia telangiectasia (AT) is an inherited cerebellar degeneration syndrome often associated with immune deficiency, notably, lymphopenia, hypogammaglobulinemia, and cellular immune dysfunction. Although autoimmunity is a common feature of many congenital and acquired immune deficiencies, it has not generally been thought to be associated with AT. We report a 7-year-old boy with AT who developed acute idiopathic thrombocytopenic purpura while on subcutaneous immunoglobulin replacement therapy for hypogammaglobulinemia. He responded promptly to high-dose intravenous immunoglobulin. This case reinforces the notion that one must be observant for autoimmune hematologic conditions in any child with qualitative or quantitative deficiencies in cellular immunity.

Haemorrhagic cystitis and polyomavirus JC infection in ataxia telangiectasia

We report the case of a young adolescent with ataxia telangiectasia (AT) and life-threatening haemorrhage from the bladder due to a combination of bladder wall telangiectasis, immunosuppressive therapy and an infection with polyomavirus JC. BK and JC are both members of the polyomavirus family. BK virus is a known cause of haemorrhagic cystitis in bone-marrow and nephropathy in kidney transplant patients, whereas JC virus is mainly associated with progressive multifocal leukoencephalopathy and only rarely found in haemorrhagic cystitis. Although opportunistic infections are uncommon in AT and virus replication was described as being down-regulated in ATM (AT mutated protein)-deficient cells, clinicians should be aware that severe haematuria in a patient with AT and undergoing immunosuppressive therapy is suggestive for polyomavirus JC-induced haemorrhagic cystitis.

Functional and computational assessment of missense variants in the ataxia-telangiectasia mutated (ATM) gene: mutations with increased cancer risk

The functional consequences of missense variants are often difficult to predict. This becomes especially relevant when DNA sequence changes are used to determine a diagnosis or prognosis. To analyze the consequences of 12 missense variants in patients with mild forms of ataxia-telangiectasia (A-T), we employed site-directed mutagenesis of ataxia-telangiectasia mutated (ATM) cDNA followed by stable transfections into a single A-T cell line to isolate the effects of each allele on the cellular phenotype. After induction of the transfected cells with CdCl2, we monitored for successful ATM transcription and subsequently assessed: 1) intracellular ATM protein levels; 2) ionizing radiation (IR)-induced ATM kinase activity; and 3) cellular radiosensitivity. We then calculated SIFT and PolyPhen scores for the missense changes. Nine variants produced little or no correction of the A-T cellular phenotype and were interpreted to be ATM mutations; SIFT/PolyPhen scores supported this. Three variants corrected the cellular phenotype, suggesting that they represented benign variants or polymorphisms. SIFT and PolyPhen scores supported the functional analyses for one of these variants (c.1709T>C); the other two were predicted to be "not tolerated" (c.6188G>A and c.6325T>G) and were classified as "operationally neutral." Genotype/phenotype relationships were compared: three deleterious missense variants were associated with an increased risk of cancer (c.6679C>T, c.7271T>G, and c.8494C>T). In situ mutagenesis represents an effective experimental approach for distinguishing deleterious missense mutations from benign or operationally neutral missense variants.

Uncommon associations with ataxia-telangiectasia: vitiligo and optic disc drusen

Ataxia-telangiectasia (A-T) is an autosomal recessive condition presented by progressive cerebellar ataxia, oculocutaneous telangiectasia, humoral and cellular immunodeficiencies and a predisposition to malignancy. We report on a 13 years old male patient with the diagnosis of A-T associated with uncommon clinical features; optic disc drusen and vitiligo. To our knowledge, this is the first report of A-T associated with these findings.

Approach to the patient with recurrent infections

Children with a history of recurrent or unusual infections present a diagnostic challenge. Differentiation between frequent infections caused by common risk factors, versus primary immune dysfunction should be based on a detailed history and physical examination and, if indicated, followed by appropriate laboratory studies. A high index of suspicion could lead to an early diagnosis and treatment of an underlying immune deficiency disease. This article presents to physicians an approach to the evaluation of children with recurrent infections. Important details from the history and physical examination, and an appropriate choice of screening laboratory test to be ordered in a given situation are discussed.

Vesical varices and telangiectasias in a patient with ataxia telangiectasia

A Japanese boy with ataxia telangiectasia (AT) developed severe gross hematuria and recurrent bladder tamponade, requiring an extensive blood transfusion. He had received intermittent intravenous cyclophosphamide pulse therapy (cumulative dose of 1.3 g) for refractory steroid-resistant and intravenous immunoglobulin-resistant severe autoimmune thrombocytopenia 3 years previously. A cystoscopy revealed multiple varices and severe telangiectasias in the bladder wall. The intensive treatment, such as repeatedly selective embolization of the vesical arteries, proved to be partially effective. Finally, a surgical cystotomy resulted in a gradual improvement in clinical symptoms. To the best of our knowledge, this is the first report of a patient with AT who developed refractory bladder hemorrhage caused by widespread vesical telangiectasias.

Immunodeficiency in ataxia telangiectasia is correlated strongly with the presence of two null mutations in the ataxia telangiectasia mutated gene

Immunodeficiency affects over half of all patients with ataxia telangiectasia (A-T) and when present can contribute significantly to morbidity and mortality. A retrospective review of clinical history, immunological findings, ataxia telangiectasia mutated (ATM) enzyme activity and ATM mutation type was conducted on 80 consecutive patients attending the National Clinic for Ataxia Telangiectasia, Nottingham, UK between 1994 and 2006. The aim was to characterize the immunodeficiency in A-T and determine its relationship to the ATM mutations present. Sixty-one patients had mutations resulting in complete loss of ATM kinase activity (group A) and 19 patients had leaky splice or missense mutations resulting in residual kinase activity (group B). There was a significantly higher proportion of patients with recurrent sinopulmonary infections in group A compared with group B (31 of 61 versus four of 19 P = 0.03) and a greater need for prophylactic antibiotics (30 of 61 versus one of 19 P = 0.001). Comparing group A with group B patients, 25 of 46 had undetectable/low immunoglobulin A (IgA) levels compared with none of 19; T cell lymphopenia was found in 28 of 56 compared with one of 18 and B cell lymphopenia in 35 of 55 compared with four of 18 patients (P = 0.00004, 0.001 and 0.003 respectively). Low IgG2 subclass levels and low levels of antibodies to pneumococcal polysaccharide were more common in group A than group B (16 of 27 versus one of 11 P = 0.01; 34/43 versus six of 17 P = 0.002) patients. Ig replacement therapy was required in 10 (12.5%) of the whole cohort, all in group A. In conclusion, A-T patients with no ATM kinase activity had a markedly more severe immunological phenotype than those expressing low levels of ATM activity.

Necrotizing vasculitis with a polyarteritis nodosa-like pattern and selective immunoglobulin A deficiency: case report and review of the literature

Selective immunoglobulin A deficiency (IgAD) is a primary immunodeficiency disease characterized by low levels (< 7 mg/dl) of serum immunoglobulin (Ig) A and normal serum levels of IgG and IgM. Patients with IgAD have increased risk for recurrent respiratory and gastrointestinal infections, autoimmune disease, asthma and allergy. A 26-year-old woman was admitted with sudden onset of painful cutaneous lesions on her lower extremities, pyrexia and arthromyalgia. Her medical history was remarkable for recurrent respiratory tract infections, self-limited episodes of acute diarrhea, atopy, splenomegaly and a 4-year history of a lung granulomatous lesion. Laboratory and imaging tests ruled out severe life-threatening infection, connective tissue disease and neoplasm. Serum protein electrophoresis showed a low IgA serum level (6.67 mg/dl), with normal serum levels of IgG and IgM, conducting to a diagnosis of selective IgAD. A skin biopsy showed necrotizing vasculitis without any sign of internal organ disease. We report a patient with IgAD and granulomatous involvement of lungs, spleen and medium-sized arteries of the skin. Although IgAD results from a failure of B-cell differentiation, we propose that deregulated immune response with production of cross-reactive antibodies and hyperstimulation of T cells and macrophages could contribute to this widespread granulomatous reaction.

Steroid-induced improvement of neurological signs in ataxia-telangiectasia patients

A recent clinical observation reported on a dramatic improvement of neurological symptoms following short-term betamethasone administration in a child affected with ataxia-teleangiectasia (A-T). The aim of this study was to extend this observation to additional A-T patients followed at a single Immunodeficiency Center. Six consecutive patients (three males; mean age 16.3 years, range 5-30 years) were enrolled into this monocentric before-after trial. A cycle of oral betamethasone at the dosage of 0.1 mg/kg/day was administered for 10 days. The neurological evaluation was performed through the Scale for the Assessment and Rating of Ataxia. Overall, five of the six patients exhibited a clear amelioration of the neurological performances. Only in two patients, a slight amelioration persisted 7 days after the therapy withdrawal, whilst in the other patients the score reached approximately the pre-treatment value at the end of the therapy. Twenty-eight of the 46 evaluated neurological items (60%) improved during therapy. The speech disturbance, finger chase and nose-finger test showed the more significant improvement. The clinical amelioration was inversely correlated with the level of cerebellum atrophy, as revealed by the magnetic resonance. Our data indicate that neurological signs in A-T are susceptible of beneficial pharmacological intervention even years after the disease onset.

Genetic immunodeficiency diseases

The approach to the patient with genetic immunodeficiency is multidisciplinary, and requires close interaction between the primary care physician, immunologist, and other specialists. Dermatologists may play a key role in both the diagnosis of immunodeficiency based on recurrent infection or specific cutaneous abnormalities and in the management of cutaneous complications. The availability of bone marrow and stem cell transplantation has been life-saving for many affected children. The underlying genetic basis is now known for most forms of immunodeficiency, which has facilitated confirmation of patient diagnosis and prenatal diagnosis. Gene therapy has already been initiated for severe combined immunodeficiency, and will certainly play a growing role in therapy of this group of disorders in the future.

Ataxia-telangiectasia and related diseases

Appropriate cellular signaling responses to DNA damage and the ability to repair DNA are fundamental processes that are required for organismal survival. Ataxia-telangiectasia (A-T) is a rare neurodegenerative disease that results from defective DNA damage signaling. Understanding the molecular basis of A-T has provided many critical insights into the cellular response to DNA double-strand breaks (DSBs). A-T is a syndrome that shows pronounced neurodegeneration of the nervous system coincident with immune deficiency, radiosensitivity, and cancer proneness. A-T results from inactivation of the A-T mutated (ATM) kinase, a critical protein kinase that regulates the response to DNA-DSBs by selective phosphorylation of a variety of substrates. Therefore, understanding the ATM signaling program has important biological ramifications for nervous system homeostasis. Underscoring the importance of the DNA-DSBs response in the nervous system are other diseases related to A-T that also result from defects in this signaling pathway. In particular, defects in the DNA damage sensor, the Mre11-RAD50-NBS1 complex, also lead to syndromes with neurological deficits and overlapping phenotypes to A-T. Collectively, these diseases highlight the critical importance of appropriate responses to DNA-DSBs to maintain homeostasis in the nervous system.

Immunodeficiency, radiosensitivity, and the XCIND syndrome

Through the analysis of a rare disorder called ataxia-telangiectasia (A-T), many important biological lessons have been gleaned. Today, it is clear that the underlying defect of A-T lies in the nucleus, as an inability to repair or process double strand breaks. More important, by the A-T phenotype now allows us to appreciate a much more general distinction between immunodeficiencies that are radiosensitive and those that are not.

Tolerance and autoimmunity: lessons at the bedside of primary immunodeficiencies

The recent progress in the genetic characterization of many primary immunodeficiencies (PIDs) allows for a better understanding of immune molecular and cellular mechanisms. The present chapter discusses associations between PIDs and autoimmune diseases (AIDs) in this new light. PIDs are classified according to the frequency of association with AIDs, defining four groups of conditions: systematic (more than 80% of all patients), strong (10-80%), mild (less than 10%), and absent (no available descriptions). Several general conclusions could be drawn: (1) pathological autoimmune (AI) manifestations are very frequently associated with PIDs, indicating that, contrary to conventional notions, antimicrobial protection and natural tolerance to body tissues share many basic mechanisms; (2) in some gene defects, association is so strong that one could speak of "monogenic" AIDs; (3) basic types of PIDs are selectively associated with AID of a particular set of target tissues; (4) while for some gene defects, current theory satisfactorily explains pathogenesis of the corresponding AID, other situations suggest extensive gaps in the present understanding of natural tolerance; and (5) not exceptionally, observations on the AI phenotype for the same gene defect in mouse and man are not concordant, perhaps owing to the limited genetic diversity of mouse models, often limited to a single mouse strain. Overall, clinical observations on PID support the new paradigm of "dominant" tolerance to self-components, in which AID owes to deficits in immune responses (i.e., in regulatory mechanisms), rather than from excessive reactivity.

Lung disease in ataxia-telangiectasia

Ataxia-telangiectasia (AT) is a multi-systemic disease caused by mutational inactivation of the ATM gene. We report a retrospective study of lung disease in 15 patients.

PATIENTS AND METHODS

A diagnosis of AT was made if the patient met the following criteria: neurological features and at least one the following: oculo-cutaneous telangiectasia, elevated serum alpha-feto-protein level.

RESULTS

Recurrent sino-pulmonary infections were usually present in 11 of the cases and occurred during the first 2 years of life. Other lung injuries noted were bronchiectasis, obstruction and restriction of the airways, fibrosis, pneumothorax and haemoptysis. Eleven children had immunodeficiencies.

DISCUSSION

Recurrent sino-pulmonary manifestations precede neurological complications, but the severity of neuro-degeneration and pulmonary disease were not correlated. Pulmonary status was a prognosis factor. Immunodeficiency was the main, but not the only, aetiology for lung disease in AT.

CONCLUSION

There is little dispute over the role of ATM in lung and respiratory epithelium. To reduce the morbidity associated with AT, there needs to be greater awareness of respiratory complications. Early management and monitoring lung function is necessary to minimize lung damage.

Regulation of Oxidative Stress Responses by Ataxia-Telangiectasia Mutated Is Required for T Cell Proliferation

Mutations in the gene encoding ataxia-telangiectasia (A-T) mutated (Atm) cause the disease A-T, characterized by immunodeficiency, the molecular basis of which is not known. Following stimulation through the TCR, Atm-deficient T cells and normal T cells in which Atm is inhibited undergo apoptosis rather than proliferation. Apoptosis is prevented by scavenging reactive oxygen species (ROS) during activation. Atm therefore plays a critical role in T cell proliferation by regulating responses to ROS generated following T cell activation. The inability of Atm-deficient T cells to control responses to ROS is therefore the molecular basis of immunodeficiency associated with A-T.

Rapid molecular prenatal diagnosis of ataxia-telangiectasia by direct mutational analysis

Mutations of the ataxia-telangiectasia-mutated (ATM) gene are responsible for the autosomal recessive disorder ataxia-telangiectasia (A-T). This study reports the first A-T prenatal diagnosis performed in Spain by direct molecular analysis. The pregnant woman had a previous child suffering from A-T due to a deletion in the ATM gene. The ATM coding region was sequenced in the A-T patient and her parents. Then, a specific polymerase chain reaction (PCR) to detect the deletion was performed for prenatal diagnosis. Additionally, polymorphic HLA loci were examined in order to exclude the possible contamination by maternal DNA. In this family of Gypsy origin, we carried out a rapid molecular diagnosis of A-T. Then, a prenatal diagnosis was carried out, identifying the deletion in the fetal DNA. Additionally, we performed a population study in unrelated Spanish Gypsies and in unrelated controls, showing that the deletion described could be a hotspot in the Spanish Gypsy population. The size of the coding region and the genomic structure, together with the absence of hotspots, make the mutation screening of the ATM gene difficult. The ability to identify ATM mutations provides a tool that can be applied in confirmatory diagnosis, genetic counselling, carrier prediction and prenatal diagnosis.

Intact T cell responses 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.

Exclusion/confirmation of ataxia-telangiectasia via cell-cycle testing

Ataxia telangiectasia (AT) is an autosomal recessive multisystem disorder with increased radiosensitivity and cancer susceptibility. The responsible gene (ATM) consists of 66 exons and a coding region of 9171 bp which precludes direct sequencing as a screening assay for confirmation or exclusion of the clinical suspicion of AT. Peripheral blood mononuclear cells of 330 patients referred for the exclusion of AT were exposed to ionizing radiation (IR) and incubated for 72 h in the presence of phytohemagglutinin. Using bivariate BrdU-Hoechst/ethidium bromide flowcytometry, the following cell cycle parameters were ascertained: (1) proportion of non-proliferating (G0,G1) cells as a measure of mitogen response, (2) proportion of first-cycle G2-phase cells relative to the growth fraction (G2/GF) as a measure of radiosensitivity. Of the cases tested, 94.2% could be unequivocally assigned either to the AT-negative or the AT-positive group of patients. Of the AT-positive cases, 11 were confirmed by ATM mutation analysis. Nineteen cases presented with non-conclusive results, mostly due to poor mitogen response; however, a combination of cell-cycle data with serum AFP concentrations led to the exclusion of AT in all but two of the uncertain cases. Substitution of ionizing radiation by the radiomimetic bleomycin was additionally tested in a small series of patients. We conclude that cell-cycle testing complemented by serum AFP measurements fulfills the criteria as a rapid and economical screening procedure for the differential diagnosis of juvenile ataxias.

Molecular pathology of ataxia telangiectasia

Ataxia telangiectasia (A-T) is one of a group of autosomal recessive cerebellar ataxias. Presentation is usually by the age of 2 years and ataxia of both upper and lower limbs develops, such that by early teenage most patients require a wheelchair for mobility. Speech and eye movement are also affected. Other important features are t(7;14) translocations, immunodeficiency, a high serum alpha fetoprotein concentration, growth retardation, telangiectasia-most noticeably on the bulbar conjunctiva-and a very high risk of developing a lymphoid tumour. Patients also show an increased sensitivity to ionising radiation. The classic form of A-T results from the presence of two truncating ATM mutations, leading to total loss of the ATM protein, a protein kinase. Importantly, A-T shows clinical heterogeneity, including milder forms where neurological progression may be slower or of later onset. In these cases there is a correlation between the preservation of neurological function, decreased radiosensitivity, and the degree of retained ATM protein kinase activity. Considerable scope remains for understanding the progress of the disorder in relation to the types of ATM mutation present.

Variability of immunodeficiency associated with ataxia telangiectasia and clinical evolution in 12 affected patients

Ataxia telangiectasia (AT) is an infrequent condition, which is difficult to diagnose in children. The objective was to describe the evolution of all affected patients controlled in our hospital and to highlight the keys for an early diagnosis considering the variability of immunological disorders. The present study is a retrospective review of all patients diagnosed and controlled of AT in our hospital. Twelve patients were found, including two couples of siblings. The most frequent reason for consultation was unstable gait. Seven patients suffered repeated infections, being pneumonia the most frequent cause of infection, followed by sinusitis. One of the patients developed Burkitt's lymphoma, and another patient, Hodgkin's lymphoma, which caused the death of the patient at the age of 11. A couple of siblings aged 17 and 22 years developed insulin-resistant diabetes mellitus. The most frequent immunity disorders were the IgG deficiency and the decrease of T lymphocytes. Seven patients were treated with non-specific gamma-globulin. By the end of the follow-up, 8 patients (ages ranged 7 to 12 years) lost gait. Molecular genetic testing was conducted in patients who are still cared for in our hospital. Clinical suspicion of this entity will lead to an early diagnosis, the treatment of complications, and to provide genetic counselling for the families.

Congenital immunodeficiencies and sepsis

OBJECTIVE

Because a hallmark of congenital immunodeficiency disorders is susceptibility to recurrent, unusual and/or severe infections, an effort was undertaken to identify a subset of these patients with an increased risk for sepsis.

DESIGN

Literature review.

RESULTS

Twenty congenital immunodeficiency disorders were identified with increased sepsis susceptibility.

CONCLUSION

Distinguishing patients with congenital immunodeficiencies from others with sepsis has important implications for the future well-being of the immunodeficient patient because many of the diseases are modified favorably by appropriate treatment. In addition, better understanding of sepsis in the setting of congenital immunodeficiency has numerous implications for both immunodeficiency and sepsis research. As a group, these disorders define components of the human immune system that are essential for defense against severe infection and demonstrate immunologic themes underlying sepsis susceptibility.

ATM and ataxia telangiectasia

Ataxia telangiectasia (AT) has long intrigued the biomedical research community owing to the spectrum of defects that are characteristic of the disease, including neurodegeneration, immune dysfunction, radiosensitivity and cancer predisposition. Following the identification of mutations in ATM (ataxia telangiectasia, mutated) as the underlying cause of the disease, biochemical analysis of this protein kinase has shown that it is a crucial nexus for the cellular response to DNA double-stranded breaks. Many ATM kinase substrates are important players in the cellular responses that prevent cancer. Accordingly, AT is a disease that results from defects in the response to specific types of DNA damage. Thus, although it is a rare neurodegenerative disease, understanding the biology of AT will lead to a greater understanding of the fundamental processes that underpin cancer and neurodegeneration.