**Abstract**

Ataxia telangiectasia (AT) is an autosomal recessive disorder characterized by cerebellar degeneration, telangiectasias, immunodeficiency, recurrent sinopulmonary infections, cancer susceptibility, and radiation sensitivity. AT is a complex disorder, whose neurological symptoms most often first appear in early childhood when children begin to sit or walk. They have immunological abnormalities: immunoglobulin and antibody deficiencies and lymphopenia. AT patients have an increased predisposition for cancers, particularly of lymphoid origin. AT is caused by mutations in the *ataxia telangiectasia mutated* (*ATM*) gene, and the role of the ATM protein is the coordination of cellular signaling pathways in response to DNA double-strand breaks, oxidative stress, and other genotoxic stresses. The diagnosis of AT is usually supported by the combination of neurological clinical features and specific laboratory abnormalities (immunoglobulin A (IgA) deficiency, lymphopenia, and increased alphafetoprotein (AFP) levels). There are several other neurological and rare disorders that physicians must consider when diagnosing AT. Treatment of neurological symptoms in patients with AT is only symptomatic and supportive, as there are no known treatments that can slow or stop neurodegeneration. However, other symptoms of AT, such as antibody deficiency, lung disease, developmental disorders, diabetes, or cancer, can be effectively treated. Some hope is associated with the treatment of dexamethasone in the patient's own blood cells, which relieves neurological symptoms.

**Keywords:** ataxia telangiectasia, immunodeficiency, radiation sensitivity, DNA double-strand breaks, ATM protein
