AT Fact Sheet
Ataxia:
AT (Ataxia Telangiectasia)
RELATED GENES:
ATM
MUTATION TYPE:
ATM -> Pathogenic variants
LOCATION:
Chromosome 11 ( 11q22.3)
HERITAGE:
Autosomal Recessive
LAST UPDATE:
September 23, 2025 by Marcio Galvão
Content generated with the support of Generative AI, reviewed by the author.
1. ABOUT AT
Ataxia telangiectasia (AT) is a rare, genetic, degenerative condition that manifests in childhood and affects multiple systems of the human body. The disease is caused by mutations in the ATM gene , which was identified in 1995 by a team of researchers in Israel. The ATM gene contains instructions for encoding (producing) a protein also called ATM. Because of the gene mutation, in people affected by AT, the ATM protein is not produced, or is produced defectively.
The ATM protein controls many important functions in cells, such as "DNA repair"—the task of orchestrating the complex response to damage to our genetic code caused by ionizing radiation. Given the importance of the ATM protein in maintaining the integrity of our DNA, which is critical for our cellular health, a lack of this protein creates problems for several systems in our body, especially the nervous, immune, and reproductive systems (Ref. [1] ). The following diagram was generated using artificial intelligence and shows, in a very simplified way, the role of the ATM protein in the DNA repair process.
2. TYPICAL SYMPTOMS
The main symptoms of AT are [1, 2] :
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Neurological difficulties (see Note 1) are the first symptoms of AT, with typical symptoms of cerebellar ataxia affecting motor coordination, balance, and difficulty walking, making the child appear "clumsy." Other neurological signs may follow, such as problems with fine motor coordination (e.g., difficulty writing by hand), involuntary movements such as tremors, abnormal eye movements, and difficulty speaking (dysarthria).
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Telangiectasias - Small blood vessels in the corners of the eyes, appearing like small "spider webs" in the conjunctiva (whites of the eyes) and in the skin of the face, ears, or in skin folds. See Note 2.
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Lung problems, respiratory infections.
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Greater sensitivity to radiation such as X-ray exposure and radiotherapy, due to the lower capacity to recover from DNA damage at the cellular level (due to the absence of the ATM protein).
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Increased risk of developing cancer (approximately 25% higher). In particular, patients with AT have a higher predisposition to developing some type of cancer, usually leukemia or lymphoma. See Note 3 .
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Weaker immune system , which can cause recurrent respiratory infections.
Notes
1 - Other neurological manifestations are choreoatosis and dystonia, which occur in 90% of patients.
2 - Telangiectasias typically appear between the ages of 3 and 5. They are generally preceded by oculomotor apraxia (difficulty moving the eyes from side to side without also moving the head).
3 - Other tumors such as medulloblastomas and gliomas occur more frequently in AT.
Source: [4]
4 - Other symptoms may appear, varying from person to person. For example, as the condition progresses, peripheral neuropathy may occur, leading to weakness or sensory loss in the hands, legs, and feet. Some children may develop insulin-resistant diabetes, and premature graying of the hair, dysphagia (difficulty swallowing), excessive salivation, and slower growth may also occur.
Variation in Severity
Source [6] distinguishes between "Classic AT" (more severe symptoms) and "Variant AT" (less severe symptoms).
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Classic AT is characterized by the early onset (in childhood) of neurological manifestations—initially cerebellar ataxia, typically followed by extrapyramidal symptoms and peripheral neuropathy, immune deficiencies, lung disease (resulting from recurrent infections due to immune deficiency, aspiration, and neurological abnormalities), and an increased cancer risk.
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Variant AT follows a much milder course. Although cerebellar ataxia may be absent, movement disorders due to extrapyramidal involvement are common—typically dystonia and tremors—and many individuals present with signs of peripheral neuropathy. Unlike Classic AT, immune function is usually normal, meaning respiratory infections and lung disease are uncommon. However, the risk of malignancy is still elevated.
3. ONSET
The diagnosis of AT can come as a shock to parents, given that there are no clear indications of the disease at birth, and most children appear healthy compared to other children in the first year of life.
Symptoms generally appear in early childhood and progressively worsen, often leading to wheelchair use around early adolescence (second decade of life, around age 10). At this stage, the child requires assistance with daily tasks due to increasing difficulty writing, increased difficulty speaking (slurred or unclear speech), difficulty reading (eye control), etc. However, AT does not cause cognitive problems, and children (and adults) with AT do not have learning or social difficulties [1] .
4. ANTICIPATION
Anticipation is not observed in AT, given that the disease "skips generations".
5. INHERITANCE
ATM is transmitted autosomal recessively . This means that individuals of both sexes have the same probability of inheriting the mutated gene. Additionally, an individual only develops symptoms of the disease if they inherit two mutated copies (alleles) of the ATM gene (one from the biological father, the other from the mother). If they inherit only one copy of the mutated gene (from either father), they will not develop the disease, but will be a carrier of the mutated gene. In people who are carriers (i.e., those who have only one mutated allele of the ATM gene), the "normal" copy of the gene takes precedence over the defective copy, and therefore carriers do not develop symptoms. In people who inherit two defective copies (pathogenic variants) of the ATM gene, the disease will manifest at some point in their lives (see Section 3. Onset ).
Probability of children inheriting the disease
Statistically, if both parents are carriers:
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The probability of each of the children developing the disease (= inheriting one mutant allele from the mother and another from the father) is 25% .
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The probability of each of the children not developing the disease and also becoming a carrier (= inheriting only one copy (allele) with the gene mutation, either from the father or the mother) is 50% .
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The probability of each child not inheriting any mutant allele (neither from the father nor from the mother) and not developing the disease nor becoming an asymptomatic carrier is 25% .
Genetic counseling
Since inheritance is hereditary (it can be passed on to future generations), once a pathogenic variant of the ATM gene has been identified in a family member, genetic counseling is recommended for adult carriers who intend to have children.
Note: "Autosomal" means the gene is located on any chromosome except the X and Y sex chromosomes. Genes, like chromosomes, typically exist in pairs (we have a pair of each gene; one copy of the gene is inherited from the mother, the other from the father). Thus, men and women are equally likely to inherit a mutated gene that can cause hereditary ataxia. "Recessive" means that two mutated copies (alleles) of the gene must be inherited (one from the biological father, the other from the mother) for a person to develop the disease.
Figure 1 - Source: MedlinePlus, US National Library of Medicine .
6. PREVALENCE
AT is estimated to occur in approximately 1 in 300,000 births (data for England). Because there are difficulties in diagnosis due to similarities with other diseases (e.g., ataxia due to cerebral palsy) and difficulties in accessing genetic testing, underreporting is likely to occur [1, 4].
7. ADDITIONAL INFORMATION
Telangiectasias that appear up to 5 years of age can help the pediatrician in the diagnosis (Figure 2).
On the one hand, the diagnosis of AT can be difficult in very young children, as they do not yet exhibit all of the characteristic symptoms and are typically less cooperative during neurological examinations.
On the other hand, the diagnosis of ataxia telangiectasia can be relatively simple in people with all the characteristic symptoms, but it can be more difficult in those with fewer symptoms.
Blood levels of a liver protein called alpha-fetoprotein are usually high, and levels of certain immunoglobulins may be low. Neurological and skin features may be noted on a physical examination.
Figure 2 - Image generated with AI support
On MRI, the typical finding is cerebellar atrophy . In laboratory tests, the concentration of alpha-fetoprotein (AFP) is higher (10 ng/mL) in approximately 95% of individuals with AT.
Diagnosis
Diagnosis of AT by molecular genetic testing (DNA tests) is available (both specific tests for the ATM gene and panels for other genes of interest, such as PP2A). For more information, see [6] .
Circumstances to avoid
According to [6] , rubella vaccination should be avoided in patients with AT who have more severe immunological problems, as this may increase the risk of granulomas. Exposure to any source of ionizing radiation (x-rays and gamma rays) should also be avoided, and radiation-based therapy is contraindicated due to the greater sensitivity of these patients to radiation, which can lead to serious complications.
Life expectancy
AT is a rare and very serious condition, which causes a reduction in the life expectancy of affected people in cases of "Classic AT", generally due to respiratory complications or cancer [4] .
8. THERAPIES AND DRUGS IN TESTS FOR AT
Consult the ACTION FOR AT portal for updates on ongoing research projects for ataxia telangiectasia, including ASO (Antisense Oligonucleotide) gene therapies and CRISPR/Cas9 gene editing.
Note! There is a 2022 study (Maryam Saberi-Karimian and colleagues) that indicates the benefits of Dexamethasone (Dexamethasone) - an orally administered anti-inflammatory drug - in improving AT symptoms.
9. TREATMENTS
There is currently no cure or treatments available to slow the progression of Ataxia-Telangiectasia (AT). However, the treatment of infections and early cancer detection can contribute to a longer and healthier life. Regular neurofunctional physical therapy, occupational therapy, and speech therapy (in cases of dysarthria and/or dysphagia), along with other supportive measures, can improve mobility, communication abilities, and overall quality of life. It is advisable that children with suspected or confirmed AT be evaluated by a pediatric neurologist or a pediatrician with clinical experience in this type of ataxia.
Source [6] recommends providing supportive care to patients with AT in order to improve quality of life and reduce the risk of complications, involving a multidisciplinary team composed of specialists in pediatric neurology, pulmonology, immunology, pediatrics (for children), and internal medicine (for adults), as well as professionals in rehabilitation medicine, physical therapy, speech-language pathology (in cases of dysarthria and/or dysphagia), occupational therapy, and nutrition. Specific cases may require support from other specialists such as oncologists, clinical geneticists, endocrinologists, orthopedists, dermatologists, and mental health professionals.
For more information on managing AT symptoms and preventing secondary complications, see the Management section in source [6].
In Brazil - It is advisable to contact the association Projeto AT Brasil, which brings together more than 100 patients with this condition and maintains connections with AT specialist researchers in the U.S. It is possible that some Brazilian patients are currently enrolled in clinical trials in the United States.
Visit the Projeto AT Brasil Facebook page.
Worldwide - Visit the following websites for more information:
See information about medications for ataxia symptoms.
See information about treatments and care for patients.
See information about those with a recent diagnosis.
See information about Support Groups for patients and caregivers.
10. REFERENCES
The references below include academic sources and specialized organizations that supported the information in this fact sheet, including peer-reviewed articles, genetic repositories (OMIM), literature summaries (GeneReviews), and informational materials from ataxia foundations. For more information, see the ataxia.info References list .
Ref #1
Source:
Action for AT website
Copyright © 2023 Action for AT
Language:
English
Date:
ND
Ref #2
Source:
AT Society website
Registered Charity No: 1105528
Language:
English
Date:
ND
Ref #3
Source:
GARD - Genetic and Rare Diseases Information Center.
Copyright © National Center for Advancing Translational Sciences - National Institutes of Health (NIH).
Language:
English
Date:
Last Updated: February 2025
Ref #4
Source:
OMIM ® - An Online Catalog of Human Genes and Genetic Disorders.
Copyright © Johns Hopkins University.
Language:
English
Date:
Edit History: carol: 06/21/2022
Ref #5
Source:
NEUROMUSCULAR DISEASE CENTER (Alan Pestronk, MD)
Washington University, St. Louis, MO - USA
Language:
English
Date:
Last Updated: Please see https://neuromuscular.wustl.edu/rev.htm
Ref #6
Source:
Stefanie Veenhuis et al
Copyright © GeneReviews. GeneReviews ® is a registered trademark of the University of Washington, Seattle.
Language:
English
Date:
Last Update: October 5, 2023.
Ref #7
Source:
Website
Copyright © 2024 AT Children's Project
Language:
English
Date:
2024
Ref #8
Source:
Osmosis from Elsevier
Youtube - Copyright © 2024 Elsevier. All rights reserved.
Language:
English
Date:
Apr 12, 2022