Mitochondrial disorders present with a wide range of symptoms and syndromes depending on the mutation and mutation load in tissues. Symptoms usually arise from the brain, nerves, skeletal and cardiac muscle, as these tissues have a high energy demand. The patients may suffer from muscle weakness, exercise intolerance, impaired balance and coordination, seizures, learning deficits, impaired vision, hearing loss and heart defects. Age at disease onset varies and the disease can debut throughout life.