Mitochondrial disorders are a group of diseases that affect mitochondrial energy metabolism (OXPHOS or electron transport chain defect). The human body breaks down foodstuffs to form energy packets (ATP) to perform all of its bodily functions. ATP is made in the mitochondria, the powerhouses of the body’s cells. Disorders affecting mitochondria result in decreased energy production and impairment of energy consuming body functions. Affected individuals can show a wide range of symptoms including any combination of developmental delays, seizures, vision and hearing problems, autonomic nervous system dysfunction (apnea, temperature instability, irregular heart rate), other heart, liver, and kidney problems, muscle weakness, and growth difficulties. The presentation and prognosis of a particular mitochondrial disorder can be very variable, even among affected individuals within the same family.