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Ataxia telangiectasia (AT) is a rare neurodegenerative genetic disorder due to bi-allelic mutations in the Ataxia Telangiectasia Mutated (ATM) gene. The aim of this paper is to better define the immunological profile over time, the clinical immune-related manifestations at diagnosis and during follow-up, and to attempt a genotype–phenotype correlation of an Italian cohort of AT patients. Retrospective data of 69 AT patients diagnosed between December 1984 and November 2019 were collected from the database of the Italian Primary Immunodeficiency Network. Patients were classified at diagnosis as lymphopenic (Group A) or non-lymphopenic (Group B). Fifty eight out of 69 AT patients (84%) were genetically characterized and distinguished according to the type of mutations in truncating/truncating (TT; 27 patients), non-truncating (NT)/T (28 patients), and NT/NT (5 patients). In 3 patients, only one mutation was detected. Data on age at onset and at diagnosis, cellular and humoral compartment at diagnosis and follow-up, infectious diseases, signs of immune dysregulation, cancer, and survival were analyzed and compared to the genotype. Lymphopenia at diagnosis was related per se to earlier age at onset. Progressive reduction of cellular compartment occurred during the follow-up with a gradual reduction of T and B cell number. Most patients of Group A carried bi-allelic truncating mutations, had a more severe B cell lymphopenia, and a reduced life expectancy. A trend to higher frequency of interstitial lung disease, immune dysregulation, and malignancy was noted in Group B patients. Lymphopenia at the onset and the T/T genotype are associated with a worst clinical course. Several mechanisms may underlie the premature and progressive immune decline in AT subjects.

Most of the ATM variants associated with Ataxia Telangiectasia are still classified as variants with uncertain significance. Ataxia Telangiectasia is a multisystemic disorder characterized by “typical” and “atypical” phenotypes, with early-onset and severe symptoms or with late-onset and mild symptoms, respectively. Here we classified the c.7157C > A ATM variant found in homozygosity in two brothers of Lebanese ethnicity. The brothers presented with an atypical phenotype, showing less than 50% of the positive criteria considered for classification. We performed several in silico analyses to predict the effect of c.7157C > A at the DNA, mRNA and protein levels, revealing that the alteration causes a missense substitution in a highly conserved alpha helix in the FAT domain. 3D structural analyses suggested that the variant might be pathogenic due to either loss of activity or to a structural damage affecting protein stability. Our subsequentin vitrostudies showed that the second hypothesis is the most likely, as indicated by the reduced protein abundance found in the cells carrying the variant. Moreover, two different functional assays showed that the mutant protein partially retains its kinase activity. Finally, we investigated thein vitroeffect of Dexamethasone showing that the drug is able to increase both protein abundance and activity. In conclusion, our results suggest that the c.7157C > A variant is pathogenic, although it causes an atypical phenotype, and that dexamethasone could be therapeutically effective on this and possibly other missense ATM variants.

Centrosomal p53 has been described for three decades but its role is still unclear. We previously reported that, in proliferating human cells, p53 transiently moves to centrosomes at each mitosis. Such p53 mitotic centrosome localization (p53-MCL) occurs independently from DNA damage but requires ATM-mediated p53Ser15 phosphorylation (p53Ser15P) on discrete cytoplasmic p53 foci that, through MT dynamics, move to centrosomes during the mitotic spindle formation. Here, we show that inhibition of p53-MCL, obtained by p53 depletion or selective impairment of p53 centrosomal localization, induces centrosome fragmentation in human nontransformed cells. In contrast, tumor cells or mouse cells tolerate p53 depletion, as expected, and p53-MCL inhibition. Such tumor- and species-specific behavior of centrosomal p53 resembles that of the recently identified sensor of centrosome-loss, whose activation triggers the mitotic surveillance pathway in human nontransformed cells but not in tumor cells or mouse cells. The mitotic surveillance pathway prevents the growth of human cells with increased chance of making mitotic errors and accumulating numeral chromosome defects. Thus, we evaluated whether p53-MCL could work as a centrosome-loss sensor and contribute to the activation of the mitotic surveillance pathway. We provide evidence that centrosome-loss triggered by PLK4 inhibition makes p53 orphan of its mitotic dock and promotes accumulation of discrete p53Ser15P foci. These p53 foci are required for the recruitment of 53BP1, a key effector of the mitotic surveillance pathway. Consistently, cells from patients with constitutive impairment of p53-MCL, such as ATM- and PCNT-mutant carriers, accumulate numeral chromosome defects. These findings indicate that, in nontransformed human cells, centrosomal p53 contributes to safeguard genome integrity by working as sensor for the mitotic surveillance pathway.

Introduction: Ataxia Telangiectasia (AT) is an autosomal recessive disorder due to mutations in the ATM gene (11q22.3), which encodes a kinase, which initiates and propagates the cellular response ...

Ataxia-telangiectasia (A-T) is a multisystem disorder caused by biallelic pathogenic variants in the gene encoding A-T mutated (ATM) kinase, a master regulator of the DNA damage response (DDR) pathway. Most A-T patients show cellular and/or humoral immunodeficiency that has been associated with cancer risk and reduced survival, but NK cells have not been thoroughly studied. Here we investigated NK cells of A-T patients with a special focus on the NKG2D receptor that triggers cytotoxicity upon engagement by its ligands (NKG2DLs) commonly induced via the DDR pathway on infected, transformed, and variously stressed cells. Using flow cytometry, we examined the phenotype and function of NK cells in 6 A-T patients as compared with healthy individuals. NKG2D expression was evaluated also by western blotting and RT-qPCR; plasma soluble NKG2DLs (sMICA, sMICB, sULBP1, ULBP2) were measured by ELISA. Results showed that A-T NK cells were skewed towards the CD56neg anergic phenotype and displayed decreased expression of NKG2D and perforin. NKG2D was reduced at the protein but not at the mRNA level and resulted in impaired NKG2D-mediated cytotoxicity in 4/6 A-T patients. Moreover, in A-T plasma we found 24-fold and 2-fold increase of sMICA and sULBP1, respectively, both inversely correlated with NKG2D expression. Overall, NK cells are disturbed in A-T patients showing reduced NKG2D expression, possibly caused by persistent engagement of its ligands, that may contribute to susceptibility to cancer and infections and represent novel targets for therapeutic interventions.

Medical advances have dramatically improved the long-term prognosis of children and adolescents with inborn errors of immunity (IEIs). Transfer of the medical care of individuals with pediatric IEIs to adult facilities is also a complex task because of the large number of distinct disorders, which requires involvement of patients and both pediatric and adult care providers. To date, there is no consensus on the optimal pathway of the transitional care process and no specific data are available in the literature regarding patients with IEIs. We aimed to develop a consensus statement on the transition process to adult health care services for patients with IEIs. Physicians from major Italian Primary Immunodeficiency Network centers formulated and answered questions after examining the currently published literature on the transition from childhood to adulthood. The authors voted on each recommendation. The most frequent IEIs sharing common main clinical problems requiring full attention during the transitional phase were categorized into different groups of clinically related disorders. For each group of clinically related disorders, physicians from major Italian Primary Immunodeficiency Network institutions focused on selected clinical issues representing the clinical hallmark during early adulthood.

Primary immunodeficiencies (PIDs) are heterogeneous disorders, characterized by variable clinical and immunological features. National PID registries offer useful insights on the epidemiology, diagnosis, and natural history of these disorders. In 1999, the Italian network for primary immunodeficiencies (IPINet) was established. We report on data collected from the IPINet registry after 20 years of activity. A total of 3352 pediatric and adult patients affected with PIDs are registered in the database. In Italy, a regional distribution trend of PID diagnosis was observed. Based on the updated IUIS classification of 2019, PID distribution in Italy showed that predominantly antibody deficiencies account for the majority of cases (63%), followed by combined immunodeficiencies with associated or syndromic features (22.5%). The overall age at diagnosis was younger for male patients. The minimal prevalence of PIDs in Italy resulted in 5.1 per 100.000 habitants. Mortality was similar to other European registries (4.2%). Immunoglobulin replacement treatment was prescribed to less than one third of the patient cohort. Collectively, this is the first comprehensive description of the PID epidemiology in Italy.

BackgroundAtaxia telangiectasia (A-T) is a neurodegenerative disorder. While patients with classic A-T generally die in their 20s, some patients with variant A-T, who have residual ataxia-telangiectasia mutated (ATM) kinase activity, have a milder phenotype. We noticed two commonly occurring ATM mutations that appeared to be associated with prolonged survival and decided to study patients carrying one of these mutations.MethodsData were retrospectively collected from the Dutch, Italian, German and French A-T cohorts. To supplement these data, we searched the literature for patients with identical genotypes.ResultsThis study included 35 patients who were homozygous or compound heterozygous for the ATM c.3576G>A; p.(Ser1135_Lys1192del58) mutation and 24 patients who were compound heterozygous for the ATM c.8147T>C; p.(Val2716Ala) mutation. Compared with 51 patients with classic A-T from the Dutch cohort, patients with ATM c.3576G>A had a longer survival and were less likely to develop cancer, respiratory disease or immunodeficiency. This was also true for patients with ATM c.8147T>C, who additionally became wheelchair users later in life and had fewer telangiectasias. The oldest patient with A-T reported so far was a 78-year-old patient who was compound heterozygous for ATM c.8147T>C. ATM kinase activity was demonstrated in cells from all patients tested with the ATM c.8147T>C mutant protein and only at a low level in some patients with ATM c.3576G>A.ConclusionCompared with classic A-T, the presence of ATM c.3576G>A results in a milder classic phenotype. Patients with ATM c.8147T>C have a variant phenotype with prolonged survival, which in exceptional cases may approach a near-normal lifespan.

Oxidative stress has been shown to play a crucial role in the pathophysiology of the neurodegenerative disease Ataxia Telangiectasia. We have recently demonstrated that Dexamethasone treatment is able to counteract the oxidative state by promoting nuclear factor erythroid 2-related factor 2 (NRF2) nuclear accumulation. However, substantial gaps remain in our knowledge of the underlying molecular mechanism(s) according to which Dexamethasone acts as an NRF2 inducer. Herein we investigate the possible effects of the drug on the main NRF2 activation pathways by initially focusing on key kinases known to differently affect NRF2 activation. Neither AKT nor ERK1/2, known to be NRF2-activating kinases, were found to be activated upon Dexamethasone treatment, thus excluding their involvement in the transcription factor nuclear shift. Likewise, GSK3 inactivating kinase was not inhibited, thus ruling out its role in NRF2 activation. On the other hand, p38 MAPK, another NRF2-inhibitory kinase, was indeed switched-off in Ataxia Telangiectasia cells by Dexamethasone-mediated induction of DUSP1 phosphatase, and therefore it appeared that it might account for NRF2 triggering. However, this mechanism was excluded by the use of a selective p38 inhibitor, which failed to cause a significant NRF2 nuclear shift and target gene induction. Finally, dexamethasone effects on the classical oxidative pathway orchestrated by KEAP1 were addressed. Dexamethasone was found to decrease the expression of the inhibitor KEAP1 at both mRNA and protein levels and to induce the shift from the reduced to the oxidized form of KEAP1, thus favouring NRF2 translocation into the nucleus. Furthermore, preliminary data revealed very low levels of the negative regulator Fyn in Ataxia Telangiectasia cells, which might account for the prolonged NRF2-activated gene expression.

Ataxia telangiectasia (A-T) is a rare incurable neurodegenerative disease caused by biallelic mutations in the gene for ataxia-telangiectasia mutated (ATM). The lack of a functional ATM kinase leads to a pleiotropic phenotype, and oxidative stress is considered to have a crucial role in the complex physiopathology. Recently, steroids have been shown to reduce the neurological symptoms of the disease, although the molecular mechanism of this effect is largely unknown. In the present study, we have demonstrated that dexamethasone treatment of A-T lymphoblastoid cells increases the content of two of the most abundant antioxidants [glutathione (GSH) and NADPH] by up to 30%. Dexamethasone promoted the nuclear accumulation of the transcription factor nuclear factor (erythroid-derived 2)-like 2 to drive expression of antioxidant pathways involved in GSH synthesis and NADPH production. The latter effect was via glucose 6-phosphate dehydrogenase activation, as confirmed by increased enzyme activity and enhancement of the pentose phosphate pathway rate. This evidence indicates that glucocorticoids are able to potentiate antioxidant defenses to counteract oxidative stress in ataxia telangiectasia, and also reveals an unexpected role for dexamethasone in redox homeostasis and cellular antioxidant activity.

Ataxia telangiectasia (A-T) is a neurodegenerative disorder. While patients with classic A-T generally die in their 20s, some patients with variant A-T, who have residual ataxia-telangiectasia mutated (ATM) kinase activity, have a milder phenotype. We noticed two commonly occurringData were retrospectively collected from the Dutch, Italian, German and French A-T cohorts. To supplement these data, we searched the literature for patients with identical genotypes.This study included 35 patients who were homozygous or compound heterozygous for theCompared with classic A-T, the presence of

Ataxia telangiectasia (A-T) is an incurable and rare hereditary syndrome. In recent times, treatment with glucocorticoid analogues has been shown to improve the neurological symptoms that characterize this condition, but the molecular mechanism of action of these analogues remains unknown. Hence, the aim of this study was to gain insight into the molecular mechanism of action of glucocorticoid analogues in the treatment of A-T by investigating the role of Dexamethasone (Dexa) in A-T lymphoblastoid cell lines. We used 2DE and tandem MS to identify proteins that were influenced by the drug in A-T cells but not in healthy cells. Thirty-four proteins were defined out of a total of 746±63. Transcriptome analysis was performed by microarray and showed the differential expression of 599 A-T and 362 wild type (WT) genes and a healthy un-matching between protein abundance and the corresponding gene expression variation. The proteomic and transcriptomic profiles allowed the network pathway analysis to pinpoint the biological and molecular functions affected by Dexamethasone in Dexa-treated cells. The present integrated study provides evidence of the molecular mechanism of action of Dexamethasone in an A-T cellular model but also the broader effects of the drug in other tested cell lines.

Ataxia telangiectasia (AT) is a rare incurable genetic disease caused by biallelic mutations in the Ataxia telangiectasia-mutated gene. Intra-erythrocyte infusion of dexamethasone improves clinical outcomes in AT patients; however, the molecular mechanisms that lead to this improvement remain unknown. Hence, to gain a better understanding of these mechanisms, we assessed the effects of glucocorticoid administration on gene expression in the blood of AT patients. Whole blood was obtained from nine children enrolled in a phase two clinical trial, who were being treated with dexamethasone (AT Dexa), from six untreated AT patients (AT) and from six healthy volunteers (WT). CodeLink Whole Genome Bioarrays were used to assess transcript expression. The reliability of the differentially expressed genes (DEGs) was verified by qRT-PCR analysis. The enriched Gene Ontology (GO) terms and the pathways of the Kyoto Encyclopedia of Genes and Genomes (KEGG) of DEGs obtained by group comparisons were achieved using the Database for Annotation, Visualization and Integrated Discovery (DAVID). Functional network analyses were computed by Reactome FI. The likely involved transcription factors were revealed by iRegulon. Among the identified DEGs influenced by the pathology and restored by dexamethasone, we detected 522 upregulated probes coding for known proteins, while 22 probes were downregulated, as they were in healthy subjects. These results provide useful information and represent a first step towards gaining a better understanding of the underlying mechanisms of the effects of dexamethasone on AT patients.

The ataxia telangiectasia mutated (ATM) protein is a pivotal multifunctional protein kinase predominantly involved in DNA damage response, as well as in maintaining overall functional integrity of the cells. Apart from playing its major role in regulating the cellular response to DNA damage, ATM, when mutated, can additionally determine oxidative stress, metabolic syndrome, mitochondrial dysfunction and neurodegeneration. In the present paper we aim to investigate the levels of oxidative stress potentially induced by the oxidizing rodent renal carcinogen KBrO3 in ATM-defective lymphoblastoid cell lines (LCLs) established from four classical AT patients (with different ATM mutations), one AT variant with reduced hypersensitivity to X rays, obligate AT heterozygotes and wild type intrafamilial control. A possible modulatory involvement of PARP in potentially induced oxidative stress is also evaluated following its inhibition with 3-aminobenzamide (3-AB). Treatments with KBrO3 clearly showed a marked hypersensitivity of the ATM-defective LCLs, including the AT variant. A marked and statistically significant reduction of KBrO3-induced chromosomal damage following inhibition of PARP by 3-AB, was observed in all AT LCLs, but not in those from the AT variant, AT heterozygotes and wild type intrafamilial control. This result is suggestive of a modulatory involvement of PARP in the hypersensitivity of ATM-defective cells to DNA oxidative damage.

DNA lesions encountered by replicative polymerases threaten genome stability and cell cycleprogression. Here we report the identification of mutations in TRAIP, encoding an E3 RING ubiquitinligase, in patients with microcephalic primordial dwarfism/Seckel syndrome. We establish that TRAIPrelocalizes to sites of DNA damage where it is required for optimal phosphorylation of H2AX andRPA2 during S-phase in response to UV irradiation, as well as fork progression through UV-inducedDNA lesions. TRAIP is necessary for efficient cell cycle progression and mutations in TRAIP thereforelimit cellular proliferation, providing a potential mechanism for microcephaly and dwarfismphenotypes. Human genetics thus identifies TRAIP as a novel component of the DNA damageresponse to replication-blocking DNA lesions.

Background Ataxia Telangiectasia (AT) is a rare incurable genetic disease, caused by biallelic mutations in the Ataxia Telangiectasia-Mutated (ATM) gene. Treatment with glucocorticoid analogues has been shown to improve the neurological symptoms that characterize this syndrome. Nevertheless, the molecular mechanism underlying the glucocorticoid action in AT patients is not yet understood. Recently, we have demonstrated that Dexamethasone treatment may partly restore ATM activity in AT lymphoblastoid cells by a new ATM transcript, namely ATMdexa1. Results In the present study, the new ATMdexa1 transcript was also identified in vivo, specifically in the PMBCs of AT patients treated with intra-erythrocyte Dexamethasone (EryDex). In these patients it was also possible to isolate new “ATMdexa1 variants” originating from canonical and non-canonical splicing, each containing the coding sequence for the ATM kinase domain. The expression of the ATMdexa1 transcript family was directly related to treatment and higher expression levels of the transcript in patients’ blood correlated with a positive response to Dexamethasone therapy. Neither untreated AT patients nor untreated healthy volunteers possessed detectable levels of the transcripts. ATMdexa1 transcript expression was found to be elevated 8 days after the drug infusion, while it decreased 21 days after treatment. Conclusions For the first time, the expression of ATM splicing variants, similar to those previously observed in vitro, has been found in the PBMCs of patients treated with EryDex. These findings show a correlation between the expression of ATMdexa1 transcripts and the clinical response to low dose dexamethasone administration. Electronic supplementary material The online version of this article (doi:10.1186/s13023-017-0669-2) contains supplementary material, which is available to authorized users.

To ensure efficient genome duplication, cells have evolved numerous factors that promote unperturbed DNA replication and protect, repair and restart damaged forks. Here we identify downstream neighbor of SON (DONSON) as a novel fork protection factor and report biallelic DONSON mutations in 29 individuals with microcephalic dwarfism. We demonstrate that DONSON is a replisome component that stabilizes forks during genome replication. Loss of DONSON leads to severe replication-associated DNA damage arising from nucleolytic cleavage of stalled replication forks. Furthermore, ATM- and Rad3-related (ATR)-dependent signaling in response to replication stress is impaired in DONSON-deficient cells, resulting in decreased checkpoint activity and the potentiation of chromosomal instability. Hypomorphic mutations in DONSON substantially reduce DONSON protein levels and impair fork stability in cells from patients, consistent with defective DNA replication underlying the disease phenotype. In summary, we have identified mutations in DONSON as a common cause of microcephalic dwarfism and established DONSON as a critical replication fork protein required for mammalian DNA replication and genome stability.

Introduction: Ataxia telangiectasia (AT) is a rare autosomal recessive disorder characterized by progressive cerebellar ataxia, oculocutaneous telangiectasias, immunodeficiency, hypersensitivity to ionizing radiation, and predisposition to malignancy. AT is caused by mutations in ataxia telangiectasia mutated (ATM) gene encoding ATM, a protein kinase responsible of DNA damage response and cell cycle control. Patients with the classical form of AT survive until the second-third decade of life; the major cause of death are lung disease due to recurrent sinopulmonary infections and cancer (T-cell leukemia and lymphoma). Treatment of primary manifestations of AT has been so far unsuccessful. Early and continued physical therapy, IVIG replacement and antibiotic treatments reduce number and severity of infections prolonging the lifespan of patients. Recently, dopaminergic drugs were shown to improve the control of movement disorders and steroids were demonstrated to dramatically reduce the neurological features...

Ataxia telangiectasia is a rare genetic disease and no therapy is currently available. Glucocorticoid analogues have been shown to improve the neurological symptoms of treated patients. In the present study ataxia telangiectasia and wild type cells were used as a cellular model and treated with dexamethasone. The cells were subsequently investigated for membrane and whole cell mechanical properties by atomic force microscopy. In addition, cytoskeleton protein dynamics and nuclear shapes were assayed by fluorescence microscopy, while western blots were used to assess actin and tubulin content. At the macro level, dexamethasone directly modified the cell shape, Young's modulus and cytoskeleton protein dynamics. At the nano level, the roughness of the cell surface and the local nano-mechanical proprieties were found to be affected by Dexa. Our results show that ataxia telangiectasia and wild type cells are affected by Dexa, although there are dissimilarities in some macro-level and nano-level features between the tested cell lines. The Young's modulus of the cells appears to depend mainly on nuclear shape, with a slight contribution from the tested cytoskeleton proteins. The current study proposes that dexamethasone influences ataxia telangiectasia cell membranes contents, cell components and cell shape.

Sequencing of sarcomere protein genes in patients fulfilling the clinical diagnostic criteria for hypertrophic cardiomyopathy (HCM) identifies a disease-causing mutation in 35% to 60% of cases. Age at diagnosis and family history may increase the yield of mutations screening. In order to assess whether Next-Generation Sequencing (NGS) may fulfil the molecular diagnostic needs in HCM, we included 17 HCM-related genes in a sequencing panel run on PGM IonTorrent. We selected 70 HCM patients, 35 with early (≤25 years) and 35 with late (≥65 years) diagnosis of disease onset. All samples had a 98.6% average of target regions, with coverage higher than 20× (mean coverage 620×). We identified 41 different mutations (seven of them novel) in nine genes: MYBPC3 (17/41 = 41%); MYH7 (10/41 = 24%); TNNT2, CAV3 and MYH6 (3/41 = 7.5% each); TNNI3 (2/41 = 5%); GLA, MYL2, and MYL3 (1/41=2.5% each). Mutation detection rate was 30/35 (85.7%) in early-onset and 8/35 (22.9%) in late-onset HCM patients, respectively (p < 0.0001). The overall detection rate for patients with positive family history was 84%, and 90.5% in patients with early disease onset. In our study NGS revealed higher mutations yield in patients with early onset and with a family history of HCM. Appropriate patient selection can increase the yield of genetic testing and make diagnostic testing cost-effective.

Here we have collected evidence suggesting that chronic changes in the NO homeostasis and the rise of reactive oxygen species bioavailability can contribute to cell dysfunction in Leber’s hereditary optic neuropathy (LHON) patients. We report that peripheral blood mononuclear cells (PBMCs), derived from a female LHON patient with bilateral reduced vision and carrying the pathogenic mutation 11778/ND4, display increased levels of reactive oxygen species (ROS) and reactive nitrogen species (RNS), as revealed by flow cytometry, fluorometric measurements of nitrite/nitrate, and 3-nitrotyrosine immunodetection. Moreover, viability assays with the tetrazolium dye MTT showed that lymphoblasts from the same patient are more sensitive to prolonged NO exposure, leading to cell death. Taken together these findings suggest that oxidative and nitrosative stress cooperatively play an important role in driving LHON pathology when excess NO remains available over time in the cell environment.

We report the case of a 6-year-old female patient with Ataxia Telangiectasia, an extremely rare condition, who developed in addition a left cerebellar astrocytoma and a right cerebellar infarction, considered as two independent events. Children with AT have an increased risk of developing cancer, but only few cases of glioma are reported and, at our knowledge, no other case of unrelated cerebellar glioma and cerebellar infarction in with the same AT patient have been described. The molecular analysis of ATM (Ataxia Telangiectasia Mutated) gene showed that the patient is compound heterozygote for two previously unreported mutations: c.3291delC (p.Phe1097fs) at exon 25 and c.8198A>C (p.Gln2733Pro) at exon 58. The role of the identified ATM gene mutations in the pathogenesis of Ataxia Telangiectasia and the coexisting cerebellar disorders is discussed.

Summary We report the case of a 19-year-old boy, presenting several congenital malformations (facial dysmorphisms, cardiac and musculoskeletal abnormalities), mental retardation, recurrent respiratory infections during growth and delayed puberty. Although previously hospitalised in other medical centres, only psychological support had been recommended for this patient. In our department, genetic, biochemical/hormonal and ultrasound examinations were undertaken. The karyotype was 49,XXXXY, a rare aneuploidy with an incidence of 1/85 000–100 000, characterised by the presence of three extra X chromosomes in phenotypically male subjects. The hormonal/biochemical profile showed hypergonadotropic hypogonadism, insulin resistance and vitamin D deficiency. The patient was then treated with testosterone replacement therapy. After 12 months of treatment, we observed the normalisation of testosterone levels. There was also an increase in pubic hair growth, testicular volume and penis size, weight loss, homeostatic model assessment index reduction and the normalisation of vitamin D values. Moreover, the patient showed greater interaction with the social environment and context. Learning points In cases of plurimalformative syndrome, cognitive impairment, recurrent infections during growth and, primarily, delayed puberty, it is necessary to ascertain as soon as possible whether the patient is suffering from hypogonadism or metabolic disorders due to genetic causes. In our case, the diagnosis of hypogonadism, and then of 49,XXXXY syndrome, was unfortunately made only at the age of 19 years. The testosterone replacement treatment, even though delayed, induced positive effects on: i) development of the reproductive system, ii) regulation of the metabolic profile and iii) interaction with the social environment and context. However, earlier and timely hormonal replacement treatment could probably have improved the quality of life of this subject and his family.

Ataxia with oculomotor apraxia type 2 (AOA2) is an autosomal recessive neurodegenerative disorder characterized by cerebellar ataxia and oculomotor apraxia. The gene mutated in AOA2, SETX, encodes senataxin (SETX), a putative DNA/RNA helicase. The presence of the helicase domain led us to investigate whether SETX might play a role in DNA damage repair and telomere stability. We analyzed the response of AOA2 lymphocytes and lymphoblasts after treatment with camptothecin (CPT), mitomycin C (MMC), H 2 O 2 and X-rays by cytogenetic and Q-FISH (quantitative-FISH) assays. The rate of chromosomal aberrations was normal in AOA2 cells after treatment with CPT, MMC, H 2 O 2 and X-rays. Conversely, Q-FISH analysis showed constitutively reduced telomere length in AOA2 lymphocytes, compared to age-matched controls. Furthermore, CPT- or X-ray-induced telomere shortening was more marked in AOA2 than in control cells. The partial co-localization of SETX with telomeric DNA, demonstrated by combined immunofluorescence–Q-FISH and chromatin immunoprecipitation, suggests a possible involvement of SETX in telomere stability.

Background: Do ATM heterozygous (ATM-htz) carriers have an increased risk of developing breast cancer? Do they have an increased sensitivity to ionizing radiation (IR)? Definitive information does not yet exist to answer these questions. Case-control studies have suggested a link between single copy ATM gene mutation and increased breast cancer risk. Lymphoblasts and skin fibroblasts from ATM-htz carriers are less sensitive to IR than cells from Ataxia Telangiectasia (AT) patients, but more sensitive than cells from the general population. Because of the clinical and environmental implication of these aspects, large studies are in progress to better understand the interaction between ATM-htz and increased breast cancer risk or radio-sensitivity. However, to be performed on the general population rather than on the obligate ATM-htz carriers, i.e., the rare parents of children affected by AT, these studies must relay on the expensive sequencing of the entire ATM gene (approximately 160Kb of genomic DNA, a 13Kb transcript of 66 exons, and more than 400 unique mutations that extend across the full length of the gene). Materials and Methods: Based on a serendipitous discovery, we have development of a new, non-invasive, easy, quick, and inexpensive test to identify AT patients and, more interestingly, the ATM-htz carriers. In particular, we found that, in mitosis, p53 localizes at centrosomes, the cytoplasmic organelles that organize the interphase cytoskeleton and contribute to bipolar spindle formation during mitotic cell division. In addition, we demonstrated that ATM is required for p53 localization at centrosome. These findings allowed us to identify a particular phenotype of peripheral blood lymphocytes (PBL) from AT patients or their parents, the obligate ATM-htz that should allow to easily discriminate the ATM-htz carries in the general population with a very high statistical significance (P Discussion: Beside an accurate assessment of the relative contribution of ATM heterozygosity to tumor susceptibility, this study will open the possibility of performing large screening for ATM-htz carries in the general population for different clinical aspects, such as IR sensitivity, genetic counseling, cancer predisposition, or selection for specific targeted therapies. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P3-06-01.

ObjectiveAtaxia-telangiectasia (AT) is a rare, severe, and ineluctably progressive multisystemic neurodegenerative disease. Variant AT phenotypes have been described in patients with mild- and late-onset neurologic deterioration and atypical features (dystonia and myoclonus). We report on the clinical characteristics and transcriptome profile of patients with a typical AT presentation and genotype who experienced an unexpected favorable course.MethodsA 24-year-old woman developed, by the age of 3 years, all the classic symptoms of AT associated with increased alpha-fetoprotein levels, a compound AT-mutated (ATM) genotype with an inframe deletion c.2250G>A (p.Glu709_Lys750del42) and a missense mutation c.8122G>A (p.Asp2708Gln), and no residual ATM protein expression. By the age of 12 years, ataxia slowly disappeared, and a very mild choreic disorder was the only neurologic feature in adulthood. Brain MRI was normal. The blood transcriptome profile was assessed and compared with that of healthy controls and patients with the classic AT phenotype.ResultsThe atypical clinical course of the patient was associated with a transitional transcriptome profile: while 90% of transcripts were expressed as in patients with the classic AT presentation, 10% of transcripts were expressed as in healthy controls.ConclusionsThe unexpected mild clinical outcome and transcriptome profile of this patient with AT suggest the existence of individual resilience to the altered ATM synthesis. Because of their possible prognostic and therapeutic implications, the identification of modifier factors affecting the phenotype would deserve further studies.

We report on a 3-year-old boy with prenatal onset of proportionate dwarfism, postnatal severe microcephaly, high forehead with receded hairline, sparse scalp hair, beaked nose, mild retrognathia and hypotonia diagnosed at birth as Seckel syndrome. At age 3 years, he became paralyzed due to a cerebrovascular malformation. Based on the clinical and radiological features showing evidence of skeletal dysplasia, the diagnosis was revised to Majewski osteodysplastic primordial dwarfism type II (MOPD II) syndrome. Western blot analysis of the patient's lymphoblastoid cell line lysate showed the absence of the protein pericentrin. Subsequent molecular analysis identified a novel homozygous single base insertion (c.1527_1528insA) in exon 10 of the PCNT gene, which leads to a frameshift (Treo510fs) and to premature protein truncation. PCNT mutations must be considered diagnostic of MOPD II syndrome. A possible role of pericentrin in the development of cerebral vessels is suggested.

In this study, the modulating effect of L-carnitine on tert-butyl-hydroperoxide-induced DNA damage was compared with that of mannitol, a well known scavenger of hydroxyl radicals, both in normal and Ataxia telangiectasia mutated (ATM)-deficient lymphoblastoid cell lines established from A. telangiectasia (A-T) patients. The alkaline version of the comet assay was employed to measure the frequency of single-strand breaks (SSBs) and alkali-labile sites induced by t-butyl-OOH immediately after treatment and at different recovery times in normal and A-T cell lines, with and without pre-treatment with L-carnitine. In addition, both the yield of induced chromosomal damage and the effect on cell proliferation were evaluated. Our results show that pre-treatment of cells with L-carnitine produced an enhancement of the rate and extent of DNA repair in A-T cell lines at early recovery time; furthermore, in samples pre-treated with L-carnitine a reduction of all types of chromosomal aberration was observed, both in A-T and in wild-type cell lines. The reducing effect of L-carnitine pre-treatment on oxidative DNA damage was more prominent than that of pre-treatment with mannitol. In conclusion, we demonstrated a protective effect of L-carnitine on oxidative stress-induced DNA damage in A-T cells, suggesting its possible role in future pharmacological applications in A-T therapy.

In Italy, little is known about the spectrum of adverse fetal effects related to maternal alcohol use during pregnancy. In this paper, we report on the phenotype of Italian children with fetal alcohol spectrum disorders (FASD). These data were gathered as part of a field study assessing the prevalence of FASD in children in an in-school study in a rural area near Rome. The purposes of this paper are: (1) to completely characterize the clinical phenotype of a large cohort of Italian children with FASD; (2) to correlate and contrast the phenotype of this population with that observed in other populations and reported in the medical literature; (3) to discuss the drinking habits of Italian women, before, during and after pregnancy; and (4) to suggest mechanisms for intervention and prevention of FASD based on data gathered from this study.

Background PIK3CA-related overgrowth spectrum (PROS) include a group of disorders that affect only the terminal portion of a limb, such as type I macrodactyly, and conditions like fibroadipose overgrowth (FAO), megalencephaly-capillary malformation (MCAP) syndrome, congenital lipomatous asymmetric overgrowth of the trunk, lymphatic, capillary, venous, and combined-type vascular malformations, epidermal nevi, skeletal and spinal anomalies (CLOVES) syndrome and Hemihyperplasia Multiple Lipomatosis (HHML). Heterozygous postzygotic PIK3CA mutations are frequently identified in these syndromes, while timing and tissue specificity of the mutational event are likely responsible for the extreme phenotypic variability observed. Methods We carried out a combination of Sanger sequencing and targeted deep sequencing of genes involved in the PI3K/AKT/mTOR pathway in three patients (1 MCAP and 2 FAO) to identify causative mutations, and performed immunoblot analyses to assay the phosphorylation status of AKT and P70S6K in affected dermal fibroblasts. In addition, we evaluated their ability to grow in the absence of serum and their response to the PI3K inhibitors wortmannin and LY294002 in vitro. Results and Conclusion Our data indicate that patients’ cells showed constitutive activation of the PI3K/Akt pathway. Of note, PI3K pharmacological blockade resulted in a significant reduction of the proliferation rate in culture, suggesting that inhibition of PI3K might prove beneficial in future therapies for PROS patients.

Ataxia-Telangiectasia is a rare multisystem autosomal recessive disorder [OMIM 208900], caused by mutations in Ataxia-Telangiectasia Mutated gene. It is characterized by neurological, immunological and cutaneous involvement. Granulomas have been previously reported in Ataxia-Telangiectasia patients, even if acne rosacea has not been described. We report a case of a young Ataxia-Telangiectasia patient with a severe immunological and neurological involvement, who developed granulomatous skin lesions diagnosed by skin biopsy as acne rosacea. Considering the severe clinical picture and the lack of improvement to multiple topic and systemic therapies, treatment with Isotretinoin was started and the skin lesions disappeared after five months. However the therapy was stopped due to drug-hepatotoxicity. Systemic treatment with Isotretinoin should be carefully considered in patient with Ataxia-Telangiectasia for the treatment of multi-drug resistant acne rosacea, however its toxicity may limit long-term use and the risk/benefit ratio of the treatment should be evaluated.

Objective: Ataxia-telangiectasia (AT) is a rare, devastating neurodegenerative disease presenting with early-onset ataxia, oculocutaneous telangiectasia, immunodeficiency, radiosensitivity, and proneness to cancer. In a previous phase 2 study, we showed that 6 monthly infusions of autologous erythrocytes loaded with dexamethasone (EryDex; EryDel, Urbino, Italy) were effective in improving neurologic impairment in young patients with AT. The present article reports the results of the extension of this study for an additional 24-month period. Methods: After the end of the first trial, 4 patients continued to be treated with monthly EryDex infusions for an additional 24 months, and their clinical outcome was compared with that of 7 age-matched patients who stopped the treatment after the first 6 infusions. The protocol included serial assessment of ataxia (by International Cooperative Ataxia Rating Scale) and adaptive behavior (by Vineland Adaptive Behavior Scales) and clinical and laboratory tests revealing treatment- and steroid-dependent adverse effects, if present. Results: Patients in the extended study experienced a continuous neurologic improvement with respect to their pretreatment status, whereas controls showed a progressive neurologic deterioration (according to the natural history of the disease) after the discontinuation of the treatment. The delivery system we adopted proved to be safe and well-tolerated, and none of the side effects usually associated with the chronic administration of corticosteroids were observed during the entire trial. Conclusions: These promising preliminary results call for a large-scale controlled study on protracted treatment of patients with AT with dexamethasone-loaded erythrocytes. Neurol

The 2005 International Workshop on Ataxia‐Telangiectasia, ATM and the DNA Damage Response took place between 8 and 11 June 2005 on the banks of Lake Maggiore, Italy. The workshop was organized by L. Chessa and D. Delia. ![][1] This workshop on ataxia‐telangiectasia marked the tenth anniversary of the discovery of the gene that is defective in this syndrome—that is, ataxia‐telangiectasia mutated ( ATM ; Savitsky et al , 1995). At the meeting, several important developments were reported, including: an expansion of the substrate repertoire of the ATM kinase; the use of animal models to analyse the signalling pathways controlled by ATM and the functional consequences of disrupting these pathways; new insights into cell‐cycle control and the maintenance of genome stability; the influence of modifier genes on ATM function; and approaches for correcting the progressive neurodegeneration that is a part of this syndrome. Ataxia‐telangiectasia is an autosomal recessive disorder characterized by neurodegeneration, immunodeficiency, hypogonadism and susceptibility to cancer. At the cellular level, it is marked by genomic instability, which is due to a defective response to double‐stranded breaks (DSBs) in DNA. This is manifested by hypersensitivity to ionizing radiation (IR) and radiomimetic compounds, and by a decreased ability to activate the DNA‐damage‐response network, which includes the cell‐cycle checkpoints (Lavin & Shiloh, 1997; Chun & Gatti, 2004). The protein product of the ATM gene is present in the nucleus as an inactive dimer or oligomer, and is activated in response to DSBs in a process that involves autophosphorylation on serine (Ser) 1,981. This causes a dissociation of the dimer to form active monomeric forms, which are able to initiate the phosphorylation of many intermediates, such as p53 and the checkpoint kinase Chk2, which are involved in DNA repair and cell‐cycle control (Bakkenist & Kastan, 2003). However, ATM is not solely responsible for initiating this … [1]: /embed/graphic-1.gif

Ataxia telangiectasia (AT) is a rare genetic disorder caused by mutations of ATM gene. ATM kinase is a "master controller" of DNA-damage response and signal transducer of external stimuli. The complex role of ATM may explain the pleiotropic phenotype characteristic of AT syndrome, only partially. In our hypothesis, the multi-faceted phenotype of AT patients might depend on specific chromatin reorganization, which then reflects on the cellular transcription. We analyzed three lymphoblastoid cell-lines isolated from AT patients and one healthy control. The three-dimensional reconstruction disclosed marked changes of nuclear morphology and architecture in AT cells. When chromatin condensation was analyzed by differential scanning calorimetry, a remodeling was observed at the level of fiber folding and nucleosome conformation. Despite the structural differences, chromatin did not exhibit modifications of the average acetylation status in comparison to the control. Moreover, AT cells presented significant alterations in the transcription of genes involved in cell-cycle regulation and stress response. In AT3RM cells, the average chromatin decondensation went with the upregulation of c-fos, c-jun, and c-myc and downregulation of metallothioneins, p21 and p53. AT9RM and AT44RM cells were instead characterized by an increased chromatin condensation and presented a different transcription unbalance. Whereas in AT44RM all the considered genes were downregulated, in AT3RM the three oncogenes and metallothioneins were upregulated, but p53 and p21 were downregulated.

The ATM-dependent accumulation of p53 and induction of p21waf1 are key events for G1 cell-cycle checkpoint arrest following DNA damage. In ATM-null AT cells, even though the p53 and p21waf1 responses are kinetically delayed and quantitatively reduced, the G1 checkpoint is virtually disrupted, suggesting that these proteins arrive too late in G1 to enforce the arrest. As the precise mechanism remains unclear, we examined the response to DNA double-strand breaks generated by gamma-radiation (IR), to determine if ATM deficiency affects the cell-cycle phase regulation of these molecules. We find that, after irradiation, whereas normal LCL-N cells markedly increase their levels of p53 in all phases of the cell cycle, AT cells fail to show any p53 increase in the G1 phase. In addition, whereas in LCL-N p21waf1 is induced in G1 and G2-M, in AT cells this induction is partly seen in G2-M, but not in G1, indicating a different cell-cycle phase regulation of p53 and p21waf1 as a result of ATM deficiency. The levels and catalytic activity of the p53-targeting kinases ATR and DNA-PK in LCL-N and AT cells are very similar throughout the cell cycle, both before and after IR, thus excluding a phase-specific activity for these kinases. Collectively, our findings demonstrate that, in ATM-deficient cells, the p53-dependent p21waf1 response to DNA damage is not only quantitatively reduced, but also specifically suppressed in the G1 phase, thus providing a mechanistic explanation for the severe disruption of the G1 checkpoint in AT cells.

A yeast-based frameshift/stop codon assay for examining ATM (ataxia telangiectasia mutated) mutations was established. Each of six fragments of a PCR-amplified coding sequence for ATM is inserted in frame by homologous recombination into a yeast URA3 fusion protein gene, and the transformants are assayed for growth in the absence of uracil. The usefulness of this assay was verified in a panel of cell lines derived from individuals with homozygous and heterozygous ATM mutations. The assay was also shown to distinguish between specimens with wild-type alleles and those with truncating mutations: a frameshift mutation or an inserted stop codon. Using this assay M059J cells, which fail to express the catalytic subunit of DNA-dependent protein kinase (PRKDC, also known as DNA-PKcs) and are hypersensitive to ionizing radiation, were found to express two different aberrant ATM transcripts: one characterized by 4776 del 133, which corresponds to the deletion of exon 33, and the other by 4909 ins 116. Subsequent analysis of the intron sequences revealed that 4909 ins 116 is comprised of a nucleotide sequence corresponding to 84013-84128 in intron 33 with a cryptic splice site. Thus the radiosensitive phenotype of M059J cells appears to be due to a defect in PRKDC and a truncating ATM mutation.

Ataxia telangiectasia (A-T) is a rare autosomal recessive disorder caused by biallelic mutations in the Ataxia Telangiectasia-mutated gene. A-T shows a complex phenotype ranging from early-onset progressive neurodegeneration to immunodeficiencies, high incidence of infections, and tumors. Unfortunately, no therapy is up to now available for treating this condition. Recently, the short term treatment of ataxia-telangiectasia patients with glucocorticoids was shown to improve their neurological symptoms and possibly reverse cerebellar atrophy. Thus, corticosteroids represent an attractive approach for the treatment of this neurodegenerative disease. However, the molecular mechanism involved in glucocorticoid action in A-T is yet unknown. The aim of our work is to construct cDNA libraries containing those genes which are transactivated by the glucocorticoid analogue, dexamethasone, in A-T human cells. For this purpose, suppression subtractive hybridization has been performed on ATM-null lymphoblastoid cell transcriptome extracted following drug administration. Annotation of whole genes contained in the libraries has been obtained by coupling subtractive hybridization with microarray analysis. Positive transcripts have been validated by quantitative PCR. Through in silico analyses, identified genes have been classified on the basis of the pathway in which they are involved, being able to address signaling required for dexamethasone action. Most of the induced transcripts are involved in metabolic processes and regulation of cellular processes. Our results can help to unravel the mechanism of glucocorticoid action in the reversion of A-T phenotype. Moreover, the induction of a specific region of the ATM transcript has been identified as putative biomarker predictive of dexamethasone efficacy on ataxic patients.

Ataxia telangiectasia (A-T) cells are sensitive to a broad range of free-radical-producing and alkylating agents. Damage caused by such agents is in part repaired by base excision [base excision repair (BER)]. Two BER pathways have been demonstrated in mammalian cells: a single-nucleotide-insertion pathway and a long-patch pathway involving resynthesis of 2–10 nucleotides. Although early studies failed to detect DNA-repair defects in A-T cells exposed to ionizing radiation and radiomimetic agents, more recent experiments performed in non-dividing A-T cells and the demonstrated interaction of the A-T-mutated protein (ATM) with the BRCA1 gene product suggest that a DNA-repair defect may underlie, at least in part, the radiation sensitivity in A-T cells. We have analysed BER of a single abasic site or a single uracil in two A-T families, using an in vitro BER system. In both families, the mutation involved was homozygous and completely inactivated the ATM protein. No difference was observed between affected individuals and heterozygous or homozygous wild-type relatives in their capacity to perform DNA repair by either one-nucleotide insertion or the long-patch pathway. Hence, the putative DNA-repair defect in A-T cells, if any, does not involve BER.

ATM (ataxia-telangiectasia mutated) gene plays a central role in the DNA-damage response pathway. We characterized the ATM protein expression in immortalized cells from AT and AT-variant patients, and heterozygotes and correlated it with two ATM-dependent radiation responses, G1 checkpoint arrest and p53-Ser 15 phosphorylation. On Western blots, the full-length ATM protein was detected in eight of 18 AT cases, albeit at 1–32% of the normal levels, whereas a truncated ATM protein was detected in a single case, despite the prevalence among cases of truncation mutations. Of two ataxia without telangiectasia [A-(T)] cases, one expressed 20% and the other ~70% of the normal ATM levels. Noteworthy, among ten asymptomatic heterozygous carriers for AT, normal amounts of ATM protein were found in one and reduced by 40–50% in the remaining cases. The radiation-induced phosphorylation of p53 protein at serine 15, largely mediated by ATM kinase, was defective in AT, A(-T) and in 2/4 heterozygous carriers, while the G1 cell cycle checkpoint was disrupted in all AT and A(-T) cases, and in 3/10 AT heterozygotes. Altogether, our study shows that AT and A(-T) cases bearing truncation mutations of the ATM gene can produce modest amounts of full-length (and only rarely truncated) ATM protein. However, this limited expression of ATM protein provides no benefit regarding the ATM-dependent responses related to G1 arrest and p53-ser15 phosphorylation. Our study additionally shows that the majority of AT heterozygotes express almost halved levels of ATM protein, sufficient in most cases to normally regulate the ATM-dependent DNA damage-response pathway. © 2000 Cancer Research Campaign

Ataxia telangiectasia (AT) is a severe autosomal recessive disease, rare but not infrequent in Italy. Owing to the seriousness of the disease, prenatal diagnosis has been attempted in the past by means of cytogenetic, biochemical, radio-biological and indirect molecular analyses. We performed the first direct molecular prenatal diagnosis of AT on a chorionic villi sample from a 37-year-old woman at the 10th week of pregnancy. She had two previous children suffering AT and two induced abortions. At molecular analysis her affected children were compound heterozygotes for mutations 7792CT in exon 55 (from the mother) and 8283delTC in exon 59 (from the father). The prenatal diagnosis was performed by two different operators in double-blind form. Mutation 7792CT was studied by restriction enzyme analysis using TaqI. Mutation 8283delTC was screened by heteroduplex analysis. The fetus was heterozygous for the mutation 7792CT (confirmed by sequencing). In order to verify the possible contamination by maternal DNA, polymorphic loci HLA-DRB1 and HLA-DQA1, together with microsatellite markers D6S259, D11S2000, D11S29, D11S1778 and D11S2179, were examined. All these loci were informative, showing that the fetus received only one allele from each parent. The heterozygosity for ATM mutation 7792CT was confirmed by molecular studies after the birth of a healthy male baby. Copyright © 1999 John Wiley & Sons, Ltd.

SummaryAtaxia-telangiectasia (A-T) is an autosomal recessive disorder characterized by cerebellar degeneration, immunodeficiency, chromosomal instability, radiosensitivity, and cancer predisposition. A-T cells are sensitive to ionizing radiation and radiomimetic chemicals and fail to activate cell-cycle checkpoints after treatment with these agents. The responsible gene, ATM, encodes a large protein kinase with a phosphatidylinositol 3-kinase–like domain. The typical A-T phenotype is caused, in most cases, by null ATM alleles that truncate or severely destabilize the ATM protein. Rare patients with milder manifestations of the clinical or cellular characteristics of the disease have been reported and have been designated “A-T variants.” A special variant form of A-T is A-TFresno, which combines a typical A-T phenotype with microcephaly and mental retardation. The possible association of these syndromes with ATM is both important for understanding their molecular basis and essential for counseling and diagnostic purposes. We quantified ATM-protein levels in six A-T variants, and we searched their ATM genes for mutations. Cell lines from these patients exhibited considerable variability in radiosensitivity while showing the typical radioresistant DNA synthesis of A-T cells. Unlike classical A-T patients, these patients exhibited 1%–17% of the normal level of ATM. The underlying ATM genotypes were either homozygous for mutations expected to produce mild phenotypes or compound heterozygotes for a mild and a severe mutation. An A-TFresno cell line was found devoid of the ATM protein and homozygous for a severe ATM mutation. We conclude that certain “A-T variant” phenotypes represent ATM mutations, including some of those without telangiectasia. Our findings extend the range of phenotypes associated with ATM mutations.

SummaryTo facilitate the evaluation of ATM heterozygotes for susceptibility to other diseases, such as breast cancer, we have attempted to define the most common mutations and their frequencies in ataxia-telangiectasia (A-T) homozygotes from 10 ethnic populations. Both genomic mutations and their effects on cDNA were characterized. Protein-truncation testing of the entire ATM cDNA detected 92 (66%) truncating mutations in 140 mutant alleles screened. The haplotyping of patients with identical mutations indicates that almost all of these represent common ancestry and that very few spontaneously recurring ATM mutations exist. Assays requiring minimal amounts of genomic DNA were designed to allow rapid screening for common ethnic mutations. These rapid assays detected mutations in 76% of Costa Rican patients (3), 50% of Norwegian patients (1), 25% of Polish patients (4), and 14% of Italian patients (1), as well as in patients of Amish/Mennonite and Irish English backgrounds. Additional mutations were observed in Japanese, Utah Mormon, and African American patients. These assays should facilitate screening for A-T heterozygotes in the populations studied.