Ataxia-telangiectasia is a rare genetic disorder that affects the nervous system, immune system, and other parts of the body. Some synonyms for this condition include A-T, Louis-Bar syndrome, cerebello-oculo-cutaneous syndrome, and Boder-Sedgwick syndrome. The term "ataxia" refers to the lack of muscle coordination and balance that is one of the hallmark symptoms of the condition. "Telangiectasia" refers to the enlarged blood vessels that often appear on the surface of the skin in individuals with A-T. Because this condition can affect many areas of the body and have a wide range of symptoms, it may be referred to by many different names depending on the context in which it is discussed.