A history of mitochondrial diseases

This articles reviews the development of mitochondrial medicine from the premolecular era (1962-1988), when mitochondrial diseases were defined on the basis of clinical examination, muscle biopsy, and biochemical criteria, through the molecular era, when the full complexity of these disorders became evident. In a chronological order, I have followed the introduction of new pathogenic concepts that have shaped a rational genetic classification of these clinically heterogeneous disorders. Thus, mitochondrial DNA (mtDNA)-related diseases can be divided into two main groups: those that impair mitochondrial protein synthesis in toto, and those that affect specific respiratory chain proteins. Mutations in nuclear DNA can affect components of respiratory chain complexes (direct hits) or assembly proteins (indirect hits), but they can also impair mtDNA integrity (multiple mtDNA mutations), replication (mtDNA depletion), or mtDNA translation. Besides these disorders that affect the respiratory chain directly, defects in other mitochondrial functions may also affect oxidative phosphorylation, including problems in mitochondrial protein import, alterations of the inner mitochondrial membrane lipid composition, and defects of mitochondrial dynamics. The enormous and still ongoing progress in our understanding of mitochondrial medicine was made possible by the intense collaboration of an international cadre of "mitochondriacs." Having published my first paper on a patient with mitochondrial myopathy 37 years ago (DiMauro et al., 1973), I feel qualified to write a history of the mitochondrial diseases, a fascinating, still evolving, and continuously puzzling area of medicine. In each section, I follow a chronological order of the salient discoveries and I show only the portraits of distinguished deceased mitochondriacs and those whose names became eponyms of mitochondrial diseases.