[Molecular pathology of mitochondrial disorders].

In the last few years morphological-cytochemical investigations and molecular genetic analysis have considerably increased the knowledge about disorders of mitochondrial functions. Molecular genetic studies have revealed that specific mutations of mitochondrial DNA are associated with specific clinical diseases and may therefore be of value in genetic counseling. Since the mitochondrial DNA is present in a high copy number in the cells a threshold exists for the biochemical manifestation of mutated mitochondrial DNA and there is no strict correlation between geno- and phenotype. Biochemical-cytochemical studies therefore are still the standard diagnostic procedures for demonstrating the clinical importance of mitochondrial mutations. During ageing similar mutations of mitochondrial DNA accumulate especially in postmitotic organs - although at a lower rate than in mitochondrial diseases - and probably contribute to the reduced organ functions in senescence.