Mitochondrial diseases often involve the brain because of the tremendous energy requirements of the brain cells. Mitochondrial diseases are very variable in their features so called clinical heterogeneity. The variability results from the fact that different organ systems contain different amounts of diseased mitochondria and only those tissues with a high percentage of diseased mitochondria will be functional impaired. Mitochondrial diseases are whole body diseases but the exact features of the disease vary from one patient to another. Some patients will have predominately brain disease or nerve disease.
Many mitochondrial diseases result in the accumulation of organic acids in the body.
These are usually normal metabolic intermediates but when present in excess, the acidosis itself may be damaging or even life-threatening. Lactic acid accumulation is a common problem in mitochondrial diseases. We used to think of mitochondrial diseases as rare childhood disorders. Recently it has been discovered that many commoner disorders such as diabetes and ischemic heart disease have, in some cases, a mitochondrial basis. Some mitochondrial diseases are clearly inherited and those involving mitochondrial DNA may be inherited through the maternal side of the family as almost all mitochondria come from the mother.