Ataxia-telangiectasia: A progressive neurodegenerative genetic disease characterized by cerebellar ataxia (incoordination and lack of balance), ocular telangiectasia ("red eyes" due to widening of small blood vessels in the conjunctiva), immune defects, and a predisposition to malignancy. Chromosomal breakage is a feature. Ataxia-telangiectasia (A-T) cells are abnormally sensitive to killing by ionizing radiation.

A-T becomes evident in early childhood, usually in the first decade of life. The hallmarks of A-T are lack of balance and slurred speech (due to the ataxia) and telangiectasias (tiny red "spider" veins), which appear in the whites of the eyes or on the surface of the ears and cheeks.

People with A-T are predisposed to leukemia and lymphoma. They are also extremely sensitive to radiation exposure. Most people with A-T have a defective immune system, making them susceptible to recurrent sinus and respiratory infections. Other features of the disease may include diabetes mellitus, premature graying of the hair, difficulty swallowing (which causes choking and drooling), and slowed growth. Children with A-T usually have and maintain normal or above normal intelligence.

There is no cure for A-T and, currently, there is no known therapy to slow the progression of the disease. Treatment is symptomatic and supportive. Physical and occupational therapy may help maintain flexibility. Speech therapy may also be useful. Intravenous immune globulin (IVIG) injections may help supplement the defective immune system. High-dose vitamin regimes have been tried. The prognosis (outlook) for people with A-T is poor. Those with the disease usually die in their teens or early 20s.

A-T is inherited as an autosomal recessive trait with both parents contributing a gene for A-T to the affected child. The gene is on chromosome 11. It is called ATM (which stands for ataxia-telangiectasia mutated). ATM encodes a protein that is predominantly confined to the nucleus of cells and that remains constant throughout all stages of the cell cycle. A disorder called the Nijmegen breakage syndrome (NBS1) is similar to A-T. The ATM and NBS1 genes appear to be in a common signaling pathway that choreographs the cell's responses to genomic damage.

See also: ATM.