Ataxia-Telangiectasia affects the nervous system, immune system, and other body systems and is characterized by progressive difficulty with coordinating movements beginning in early childhood leading to difficulty walking, problems with balance and hand coordination, involuntary jerking movements, muscle twitches, and disturbances in nerve function. 

People often have a weakened immune system, and many develop chronic lung infections and are also at an increased risk of developing cancer, particularly leukemia and lymphoma.  Although people with ataxia-telangiectasia usually live into adulthood, their life expectancy is reduced.