What Is the ATM Gene and How Does It Affect Health?

The ATM gene provides instructions for making a large protein kinase that acts as one of the body’s most important guardians against DNA damage. When the gene works normally, its protein detects broken DNA strands and orchestrates the repair process, keeping cells from accumulating the kind of genetic errors that lead to cancer. When ATM is disrupted, the consequences range from a severe childhood neurological condition called ataxia-telangiectasia (when both copies of the gene are lost) to a moderately elevated cancer risk (when just one copy carries a harmful variant). The gene’s influence reaches further than most people expect, touching immunity, fertility, cellular aging, and even how a person responds to radiation therapy.

What the ATM Protein Actually Does

ATM stands for “ataxia-telangiectasia mutated,” named after the disease that led to its discovery. The gene was identified in 1995 through positional cloning on chromosome 11, and its protein turned out to resemble a class of enzymes already known to be involved in cell signaling.¹ Everyone carries two copies of ATM, one inherited from each parent. The protein it encodes sits in an inactive state inside cells until something goes wrong with DNA.

The most critical job of ATM is responding to double-strand breaks, which are among the most dangerous forms of DNA damage. When both strands of the DNA helix snap, a sensor complex detects the break and recruits ATM to the site, triggering a cascade of chemical signals that pause the cell cycle, summon repair machinery, and, if the damage is beyond repair, push the cell toward self-destruction.² Without this system, broken DNA gets passed to daughter cells, piling up mutations that can eventually drive cancer.

ATM does not work alone. A related kinase called ATR responds to a different kind of DNA stress, particularly problems that arise when DNA is being copied. Although the two kinases respond to distinct triggers, they share many of the same downstream targets and can partially back each other up.³ That partial overlap is why losing ATM is survivable: ATR picks up some of the slack. But the redundancy is incomplete, and the gaps show up as disease.

ATM’s Surprising Role in Oxidative Stress

For years, researchers thought of ATM mainly as a DNA-break responder. That picture has expanded considerably. ATM also functions as a sensor of oxidative stress, a form of cellular damage caused by reactive oxygen species. When levels of these molecules climb too high, ATM can be activated independently of any DNA breaks, triggering pathways that boost the cell’s antioxidant defenses.⁴

One key mechanism involves the pentose phosphate pathway, a metabolic route that generates a molecule called NADPH, which cells need to neutralize reactive oxygen species. ATM promotes the activity of an enzyme at the entrance of this pathway, effectively cranking up the cell’s ability to mop up oxidative damage. Cells without functional ATM show impaired mitochondrial respiration, lower membrane potential, and elevated levels of mitochondrial reactive oxygen species. ATM even localizes to mitochondria themselves and can be activated by mitochondrial damage in the complete absence of nuclear DNA lesions.⁵ This dual role helps explain why ATM loss causes problems in tissues that are not dividing rapidly and rarely encounter double-strand breaks, like neurons in the cerebellum.

Ataxia-Telangiectasia, the Full-Loss Condition

When a child inherits two nonfunctional copies of ATM, one from each parent, the result is ataxia-telangiectasia, often shortened to A-T. It is a rare autosomal recessive disorder, meaning both parents must be carriers for a child to be affected. A-T typically becomes apparent in early childhood when a toddler begins to show progressive difficulty with balance and coordination, the hallmark cerebellar ataxia.

The neurological decline is driven by loss of Purkinje cells in the cerebellum. Research in primate models has confirmed that ATM-deficient animals develop cerebellar atrophy, significant Purkinje cell loss, and motor impairments that mirror the human disease, along with growth retardation, elevated alpha-fetoprotein, and dilated blood vessels on the skin and eyes called telangiectasias.⁶ Vascular abnormalities extend to the retina as well: mouse models of A-T show reduced retinal blood flow, leaky vessels, and progressive functional deficits in vision even at young ages, suggesting that vascular problems may worsen the neurodegeneration.⁷

The immune system is also hit hard. A-T produces a highly variable immune deficiency that, in some patients, leads to recurrent lung and sinus infections severe enough to be a major cause of illness and death.⁸ Respiratory problems in A-T go beyond infections, though. A European Respiratory Society statement notes that swallowing dysfunction from the underlying neurodegeneration causes aspiration, cough becomes inefficient, and some patients develop interstitial lung disease or pulmonary fibrosis.⁹

Cancer Risk in People With A-T

Children with A-T face a dramatically elevated risk of developing cancer, estimated at roughly 25% over their lifetime, with blood cancers predominating.¹⁰ In a large international series of over 200 children with A-T and blood cancers, about 45% presented with mature B-cell lymphomas, 41% with acute lymphoblastic leukemia or lymphoma, and 10% with Hodgkin lymphoma.¹¹ Treating these cancers is complicated by the fact that many standard chemotherapy and radiation protocols are themselves DNA-damaging, and A-T patients are exquisitely sensitive to such damage. Oncologists must carefully adjust treatment intensity.

Cancer Risks for Carriers With One Working Copy

Far more common than A-T is the situation where a person carries one functional and one nonfunctional copy of the ATM gene. Roughly 1 to 2% of the general population falls into this category, usually without knowing it. These carriers do not develop ataxia-telangiectasia, but they do face moderately increased cancer risks across several organ systems.

Breast cancer is the best-studied association. Women carrying a single harmful ATM variant have a lifetime breast cancer risk of roughly 20 to 25%, compared with about 12% in the general female population.¹²¹³ The majority of ATM-related breast cancers are estrogen-receptor-positive, which has implications for treatment options.

The risk extends beyond the breast. A large study of germline variants found that the strongest cancer association for ATM carriers was with pancreatic cancer, where carriers faced roughly a fourfold increase in risk. Gastric and prostate cancers also showed marked elevations.¹⁴ For pancreatic cancer specifically, a systematic review found that after BRCA2, ATM had the highest frequency of harmful germline variants among people diagnosed with the disease.¹⁵ The same ACMG guideline notes that analysis from a large prostate cancer consortium found ATM carrier status associated with more than a fourfold increase in lifetime prostate cancer risk and a higher chance of early-onset disease.

Screening Recommendations for ATM Carriers

Given these elevated risks, medical guidelines have begun to address screening for people who learn they carry an ATM variant. For breast cancer, modeling studies suggest that annual mammography alone starting at age 40 reduces mortality by about 36 to 39%. Adding annual MRI starting at age 30 to 35, followed by combined MRI and mammography from age 40, can push that mortality reduction above 50%.¹² The tradeoff is a higher rate of false-positive results and benign biopsies, which is worth discussing with a healthcare provider but generally considered acceptable given the stakes.

For pancreatic cancer, some guidelines now recommend that ATM carriers with a family history of the disease consider surveillance with endoscopic ultrasound or MRI, though the evidence for pancreatic screening in any population remains thinner than for breast screening. Prostate cancer screening conversations for male carriers should start earlier than typical guidelines suggest, given the association with early-onset disease.

Radiation Sensitivity and Treatment Decisions

One of the most clinically consequential aspects of ATM variants is their potential effect on how people respond to radiation therapy. ATM’s core job is repairing the exact kind of damage that radiation inflicts, so it makes biological sense that a person with reduced ATM function might handle radiation poorly. The clinical reality, however, is not straightforward.

Some carriers tolerate standard radiation without unusual side effects, while others develop unexpectedly severe reactions. Case series have documented patients with ATM variants who experienced sudden severe skin toxicity at moderate radiation doses, while other carriers receiving higher doses had only mild reactions.¹⁶ Among prostate cancer patients treated with brachytherapy, possession of ATM sequence variants, particularly those causing amino acid substitutions, was predictive of adverse radiotherapy responses.¹⁷

For breast cancer specifically, a large epidemiological study found that women carrying rare, predicted-deleterious ATM variants who were exposed to radiation had a significantly higher risk of developing cancer in the opposite breast compared to unexposed women with the same variants, with risk ratios in the range of 3 to 6.¹⁸ This does not mean radiation therapy is always contraindicated for ATM carriers. Some data even suggest improved tumor response to radiation in certain carriers. The evidence remains mixed, which means the decision to use radiation for an ATM carrier with cancer often requires careful individual assessment and a frank discussion about uncertainty.¹⁹

The Problem of Variants of Uncertain Significance

Genetic testing for ATM variants is increasingly accessible through both clinical panels and direct-to-consumer services. But the results are not always clear-cut. Many people who undergo testing receive a result classified as a “variant of uncertain significance,” or VUS. This means the lab found a change in the ATM gene, but there is not yet enough evidence to say whether that change is harmful or harmless.

This is a real and growing challenge. ATM is a large gene, and the sheer number of possible changes means that many detected variants have been seen only a handful of times, not enough to determine their effect. Research has highlighted the need to resolve the pathogenicity of these variants, because the difference between a VUS and a confirmed pathogenic variant has major implications for cancer surveillance, family testing, and treatment decisions.²⁰ If you receive a VUS result for ATM, the standard recommendation is to follow up with a genetic counselor and not to make drastic medical decisions based on the VUS alone, since its classification may change as more data accumulate.

Targeted Therapies That Exploit ATM Loss

While ATM deficiency is a vulnerability for the patient, it is also a vulnerability for the tumor, and researchers are trying to turn that weakness against cancer cells. Tumors that have lost both copies of ATM are impaired in a major DNA repair pathway called homologous recombination. This opens them up to a class of drugs called PARP inhibitors, which block a backup DNA repair route, creating a situation where the cancer cell has no way to fix its DNA and dies.

Laboratory studies have shown that cells completely lacking ATM are sensitized to the PARP inhibitor niraparib, and in patient-derived tumor models of non-small cell lung cancer carrying two ATM-damaging mutations, niraparib caused significant tumor shrinkage in about a third of cases.²¹ This approach mirrors what has already been done successfully in BRCA-mutated cancers and is an active area of clinical investigation. Other DNA-damaging agents like platinum chemotherapy drugs are also being explored for ATM-deficient tumors, though prospective clinical trials are still needed to confirm benefit in patients.

Experimental Treatments for Ataxia-Telangiectasia

For the children living with full A-T, treatment has historically been limited to managing symptoms: physical therapy for coordination problems, antibiotics and immunoglobulin replacement for immune deficiency, and careful cancer surveillance. No approved therapy restores ATM function. But several experimental approaches are generating cautious optimism.

Antisense oligonucleotides, or ASOs, are short synthetic molecules that can correct errors in the way the ATM gene’s instructions are read. Many A-T patients carry mutations that cause the cellular machinery to misread the gene, producing truncated, useless protein. ASOs can redirect this machinery to read the gene correctly, restoring production of full-length, functional ATM protein. In laboratory studies using patient-derived cells, ASOs successfully restored ATM protein and reduced sensitivity to radiation damage. The technique was replicated across multiple different splice-site mutations, and researchers have shown that by attaching the ASOs to cell-penetrating peptides, they can reach the cerebellum in mice after intravenous injection, with detectable ATM levels persisting for at least three weeks after a single treatment.²²

A different approach targets patients whose ATM gene contains a premature stop signal, causing protein production to halt partway through. Small molecules called read-through compounds can trick the cell into ignoring the premature stop and completing the full protein. Researchers have identified compounds that work across all three types of nonsense mutations found in ATM patients, restoring some functional protein in patient-derived cells.²³ Both approaches remain preclinical, but they represent the first realistic avenues toward treating the underlying genetic cause of A-T rather than just its symptoms.

ATM’s Role in Cellular Aging

ATM turns up in research on aging in a way that was not initially obvious. As cells age, their telomeres (the protective caps on chromosome ends) shorten. When telomeres become critically short, the exposed chromosome ends resemble double-strand breaks, and the cell’s DNA damage alarm goes off. ATM is the kinase that reads those alarms. In senescent human cells, telomeric damage foci form and signal through ATM to activate growth-arrest pathways. When researchers blocked ATM activity in those cells, the senescent cells re-entered the cell cycle, meaning they started dividing again despite their damaged chromosomes.²⁴ This indicates that ATM-driven signaling is required for the stable arrest that keeps damaged old cells from becoming dangerous. The connection to aging biology is still being explored, but it adds another dimension to ATM’s role as a genome guardian: not just fixing acute damage, but also enforcing the permanent retirement of cells that have accumulated too much wear.

ATM and Fertility

ATM plays a specific role in the development of sperm cells. During the process of making sperm, cells must deliberately create and then repair double-strand breaks as part of genetic recombination, the shuffling of parental DNA that ensures each sperm is genetically unique. ATM helps manage this controlled demolition and rebuilding.²⁵ When recombination intermediates persist longer than they should, ATM-dependent signaling enforces a checkpoint that pauses the process, giving the cell time to finish repairs or, if that fails, triggering the cell’s death to prevent defective sperm from being produced.²⁶ Male patients with A-T typically show reduced fertility, and male mice lacking ATM are sterile. Female fertility is also affected, though the mechanisms are less thoroughly characterized. For carriers with one working copy, fertility is generally normal, but the gene’s involvement in germ cell quality control is one more illustration of how deeply embedded ATM is in basic cellular housekeeping.