Ataxia Telangiectasia Syndrome

**Semantic type:** Disease or Syndrome

**Definition:** Rare hereditary disease characterized by extreme sensitivity to ionizing radiation or radiomimetic drugs because of a defect in DNA repair. AT heterozygosity is estimated to occur in more than 2% of the U.S. population; heterozygotes exhibit increased radiation sensitivity and are at increased risk for several types of cancer. The normal version of the gene that is defective in AT appears to activate the p53-dependent response to DNA damage.

**Synonyms:** - Ataxia Telangiectasia - Ataxia-Telangiectasia Syndrome - Ataxia-telangiectasia - Louis-Bar Syndrome - ataxia-telangiectasia