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Puneet Opal, MD, PhD
Francisco A Bonilla, MD, PhD
Section Editors
Marc C Patterson, MD, FRACP
E Richard Stiehm, MD
Deputy Editor
John F Dashe, MD, PhD


Hereditary ataxia has a variety of causes. One cause is an autosomal recessive disorder associated with defective DNA repair mechanisms: ataxia-telangiectasia (AT; MIM 208900). Patients with AT develop progressive cerebellar ataxia, abnormal eye movements, other neurologic abnormalities, oculocutaneous telangiectasias, and immune deficiency.

This topic will review the genetics and clinical aspects of AT. A closely related disorder, ataxia-telangiectasia-like disorder (ATLD), is also discussed in this review. (See 'Ataxia-telangiectasia-like disorder' below.)

The hereditary ataxias are reviewed elsewhere. (See "Overview of the hereditary ataxias".)


Ataxia-telangiectasia (AT) is an autosomal recessive genetic disorder. The defective gene in AT has been mapped to chromosome 11q22.3, and designated the ATM gene (for AT Mutated) [1,2]. The ATM gene product has one region similar to that of phosphatidylinositol (PI)-3 kinases and another region similar to DNA repair/cell checkpoint genes. It is expressed in all tissues in the body.

ATM is involved in the detection of DNA damage, and plays an important role in cell cycle progression [3]. The latter function is exerted at the transition between the G1 and S phase, when a cell initiates DNA synthesis in preparation for DNA replication. It also functions at the G2 to M transition, during which the cell begins to divide.


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