Ataxia telangiectasia (A-T) is a rare genetic disorder that progressively damages the nervous system and immune system, typically appearing in early childhood. It affects roughly 1 in 40,000 to 1 in 100,000 births worldwide, with all races and ethnicities affected equally. The condition is caused by mutations in a single gene responsible for repairing damaged DNA, which leads to a cascade of problems: worsening coordination, weakened immunity, and a significantly elevated cancer risk.
What Causes A-T
A-T is an autosomal recessive condition, meaning a child must inherit a faulty copy of the ATM gene from both parents to develop the disease. Parents who each carry one mutated copy typically have no symptoms themselves.
The ATM gene produces a protein that acts as a master alarm system inside your cells. When DNA suffers a double-strand break, one of the most dangerous types of genetic damage, the ATM protein detects it and triggers a coordinated response: it halts cell division so the damage doesn’t spread, activates repair crews, and if the damage is too severe, signals the cell to self-destruct rather than become cancerous. Without functioning ATM protein, cells can’t accurately repair broken DNA. Over time, this leads to accumulating genetic errors, particularly in cells that divide frequently, like immune cells and certain brain cells.
This repair deficit also makes cells from people with A-T dramatically sensitive to ionizing radiation, such as X-rays. That sensitivity is important to know about because it affects how cancers in A-T patients can be treated.
Early Signs and Neurological Decline
The hallmark symptom is ataxia, a progressive loss of coordination that usually appears before age 2 in the classic form of the disease. Parents often first notice their child having trouble walking, with an unsteady, wide-based gait. What initially looks like it might be a mild developmental delay becomes clearly progressive over the following years.
Beyond basic coordination, A-T affects multiple aspects of movement. Children develop difficulty controlling eye movements (a feature called oculomotor apraxia), making it hard to track objects smoothly or shift gaze on command. Involuntary movements like dystonia and myoclonus appear as the disease progresses, with myoclonus being especially common in A-T compared to similar conditions. Peripheral neuropathy, damage to the nerves in the hands and feet, adds another layer of difficulty. In the classic form, most children become wheelchair-dependent around age 10.
Milder forms of A-T do exist. Some individuals develop ataxia later in childhood or even adolescence, with slower progression and delayed or absent wheelchair dependency. In these cases, the neurological picture can be limited to mild cerebellar symptoms for years, with onset anywhere from age 1.5 to the early twenties.
Telangiectasias and Other Visible Signs
The second part of the disease’s name refers to telangiectasias: tiny, dilated blood vessels that become visible on the surface of the skin and eyes. These typically appear between ages 3 and 6, most often on the whites of the eyes and on sun-exposed areas like the ears and cheeks. They’re not painful or dangerous on their own, but they’re a distinctive clinical clue that helps distinguish A-T from other childhood ataxias.
Immune Problems and Infections
Most people with A-T have some degree of immune deficiency, though its severity varies widely. The immune system relies on cells that must rearrange their DNA to produce antibodies and fight infections, a process that depends heavily on the same DNA repair machinery that A-T disrupts. The result is often low levels of certain antibody types, reduced numbers of infection-fighting white blood cells, or both.
In practical terms, this means frequent respiratory infections: sinus infections, bronchitis, and pneumonia. Over time, repeated lung infections can cause lasting damage, a condition called bronchiectasis, where the airways become permanently widened and scarred. Respiratory complications, including pneumonia and chronic lung disease, are one of the leading causes of death in A-T.
Cancer Risk
Between 30 and 40 percent of people with A-T develop cancer during their lifetime. About 80 percent of those cancers are lymphoid, meaning they arise from the immune system itself, primarily lymphomas and leukemias. This makes sense given the underlying biology: immune cells undergo extensive DNA rearrangement as part of their normal development, and without proper ATM-mediated repair, these rearrangements go wrong at a much higher rate.
Cancer treatment in A-T is complicated by the extreme radiation sensitivity of the patient’s cells. Standard chemotherapy regimens and radiation therapy can cause severe, even fatal, side effects at doses that would be routine for other patients. Oncologists treating someone with A-T must use modified protocols with reduced doses.
How A-T Is Diagnosed
Diagnosis usually begins when a young child presents with progressive ataxia that can’t be explained by other causes. Several key findings point toward A-T specifically.
- Elevated alpha-fetoprotein (AFP): This blood protein, normally high in newborns but declining to low levels by age 1, remains persistently elevated in A-T. Levels above 65 micrograms per liter are highly suggestive of A-T, as opposed to similar conditions where AFP is lower or normal.
- Low or absent ATM protein: Lab tests can directly measure ATM protein levels in blood cells or assess how well cells respond to radiation-induced DNA damage.
- Genetic testing: Sequencing the ATM gene confirms the diagnosis by identifying the specific mutations.
- Immune markers: Blood tests often reveal low immunoglobulin levels and reduced lymphocyte counts.
The AFP threshold is particularly useful for distinguishing A-T from two conditions that look similar: ataxia with oculomotor apraxia types 1 and 2 (AOA1 and AOA2). Both share features like early-onset ataxia, difficulty with eye movements, nerve damage, and cerebellar shrinkage on brain imaging. However, AOA1 tends to have AFP levels between 7 and 15 micrograms per liter, AOA2 between 15 and 65, while A-T consistently exceeds 65. AOA1 and AOA2 also lack the visible telangiectasias and the recurrent infections that characterize A-T.
Treatment and Daily Management
There is currently no cure for A-T and no treatment that slows the neurological progression. Management focuses on addressing each of the disease’s components as they arise.
For the immune deficiency, some individuals benefit from immunoglobulin replacement therapy, which provides the antibodies their own immune system can’t produce in sufficient quantities. Aggressive treatment of respiratory infections and proactive pulmonary care, including chest physiotherapy, help preserve lung function for as long as possible. Physical and occupational therapy can help maintain function and adapt to changing abilities as motor control declines. Speech therapy becomes important as the muscles involved in speaking and swallowing are affected.
Cancer surveillance is a routine part of care, given the high malignancy risk. Because standard imaging with CT scans involves radiation, clinicians generally prefer MRI and ultrasound when possible.
Life Expectancy
Median survival for people with classic A-T falls between 19 and 25 years, based on two large patient cohorts, one prospective and one retrospective. The range is wide, and some individuals with milder forms of the disease live significantly longer. The most common causes of death are cancer (and complications of its treatment), respiratory infections like pneumonia, and chronic lung disease. A smaller number of patients experience acute neurological deterioration related to abnormal blood vessel formations in the brain.
Many of these deaths come from relatively sudden complications, particularly cancer or acute infections, rather than a slow, predictable decline. This unpredictability is one of the more difficult aspects of the disease for families, as the severity of someone’s neurological or immune problems at any given point doesn’t reliably predict their overall prognosis.