The rationale for the use of this agent is indirect. Over the past 10 years, defects in mitochondrial oxidative phosphorylation (OXPHOS) have been implicated in a wide variety of neurodegenerative and neuromuscular diseases. One neurological symptom that has definitely been associated with OXPHOS is the movement disorder dystonia. A specific missense mutation in the mtDNA complex I (NADH dehydrogenase) gene, MTND6, has been linked to maternally inherited dystonia along with the companion phenotype, Leber's hereditary optic neuropathy. In addition, other mitochondrial diseases are also associated with movement disorders including Friedreich's ataxia (ataxia) and Leigh's disease (loss of head control and other motor skills). EPI-743 has been effective in treating children and adults with these diseases. Over time, many TS patients develop complex motor tics, which are sudden, more purposive appearing, stereotyped movements of variable duration. Examples are myriad and include facial gestures and movements such as brushing hair back, possibly in combination with head jerk, and body shrugs. Gyrating, bending, and twisting movements of the head or torso are also seen. These slow twisting movements are usually referred to as dystonic tics.