Diagnosis of the mitochondrial encephalomyopathies.

In few fields of medicine has recent progress been as fast and exciting as in the area of mitochondrial diseases. Although the clinical manifestations of mitochondrial dysfunction are extremely variable, biochemical and genetic classification of these disorders is now possible and recent advances in morphologic analysis and genetic testing aid in the identification of patients. What makes these diseases uniquely interesting from a genetic point of view is the fact that mitochondria contain their own DNA, which has distinct genetic properties. It is in the area of mitochondrial DNA defects that there has been extraordinary progress in the past few years, and a new chapter of human genetics, "mitochondrial genetics," has opened up and is becoming increasingly important in the differential diagnosis and in genetic counseling.