ABSTRACT
About 3000 genes are necessary for growth, maintenance, and recycling of mitochondria. Thirty-seven of these genes are encoded by mitochondrial DNA (Figure 8.1), with the nucleus harboring the remainder. Mutations in both mtDNA and nuclear genes cause mitochondrial diseases. Mitochondrial diseases most often affect children, and many are lethal. However, adult-onset or age-dependent mitochondrial diseases are becoming more common. Dysfunctional mitochondria appear to cause the most damage to cells of the brain, heart, liver, skeletal muscles, kidney, and endocrine and respiratory systems. Some symptoms of mitochondrial diseases include muscle weakness and pain, loss of motor control, gastrointestinal disorders, swallowing difculties, poor growth, cardiac disease, liver disease, diabetes, respiratory complications, seizures, visual and hearing problems, mild to fatal lactic acidosis, developmental delays, and susceptibility to infection. This wide range of symptoms is not surprising given that mitochondria produce more than 90 percent of the energy needed by the body to sustain life.
