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. Most inherited mitochondrial diseases however are so called nuclear DNA defects with inheritance from either the mother or father, or in most cases both. Most childhood onset mitochondrial diseases are inherited although in some cases the affected child seems to be the only affected family member. Diseases resulting from mitochondrial deletions of large parts of the mitochondrial DNA molecule are usually sporadic without other affected family members.
Genetic counselling is complex for mitochondrial diseases.
Pre-natal testing is only available for a few disorders. Because of the multiple organ systems involved and the variation in the age of onset, mitochondrial diseases may be difficult to recognize. Even within the same family the same disease may affect individuals differently. A severe childhood disease such as Leigh s syndrome may occur in the same family with later onset adult neurodegenerative disease. In some families mitochondrial myopathy has found some members with deafness and diabetes in others strokes along with a mixture of other symptoms.