Ataxia telangiectasia (AT) is a complex genetic neurodegenerative disorder that may become apparent during infancy or early childhood. The disorder is characterized by progressively impaired coordination of voluntary movements (ataxia), the development of reddish lesions of the skin and mucous membranes due to permanent widening of groups of blood vessels (telangiectasia), and impaired functioning of the immune system (i.e., cellular and humoral immunodeficiency), resulting in increased susceptibility to upper and lower respiratory infections (sinopulmonary infections). Individuals with AT also have an increased risk of developing certain malignancies, particularly of the lymphatic system (lymphomas), the blood-forming organs (e.g., leukemia), and the brain.
In those with AT, progressive ataxia typically develops during infancy and may initially be characterized by abnormal swaying of the head and trunk. As the disease progresses, the condition leads to an inability to walk (ambulation) by late childhood or adolescence. Ataxia is often accompanied by difficulty speaking (dysarthria), drooling; and an impaired ability to coordinate certain eye movements (oculomotor apraxia), including the occurrence of involuntary, rapid, rhythmic motions (oscillations) of the eyes while attempting to focus upon certain objects (fixation nystagmus). Affected children may also develop an unusually stooped posture and irregular, rapid, jerky movements that may occur in association with relatively slow, writhing motions (choreoathetosis). In addition, telangiectasias may develop by mid-childhood, often appearing on sun-exposed areas of the skin, such as the bridge of the nose, the ears, and certain regions of the extremities, as well as the mucous membranes of the eyes (conjunctiva).
AT is inherited as an autosomal recessive trait. The disorder is caused by changes (mutations) of a gene known as ATM (for "AT mutated") that has been mapped to the long arm (q) of chromosome 11 (11q22.3). The ATM gene controls (encodes for) the production of an enzyme that plays a role in regulating cell division following DNA damage.