Mitochondrial diseases used to be considered rare childhood disorders. Recently it has been discovered that many commoner diseases such as diabetes and ischaemic heart disease have, in some cases, a mitochondrial basis. Also, diseases of aging such as Parkinson's disease and Alzheimer's disease may result in part from mitochondrial failure. The aging process itself may be due to a lifetime of damage in mitochondria through oxidative stress and accumulated damage in mitochondrial proteins and mitochondrial DNA.
Most childhood onset mitochondrial diseases are inherited although in some cases the affected child seems to be the only affected family member. Mitochondria can be damaged by some drugs producing mitochondrial disease and it seems likely that high fat diets and perhaps environmental toxins contribute to the mitochondrial injury of old age. In the case of late onset adult diseases involving mitochondria, the current theory is that there are multiple contributing causes.