[The history of mitochondrial encephalomyopathies]

At the end of the XIXth century, the first cases of primary progressive ophthalmoplegia reported were related to a primary degeneration of the oculomotor nuclei; and this concept was accepted until there were considered of purely muscular origin in the 1950's. From this time and during twenty years these cases were reported as ocular myopathies. However the coexistence of neurological abnormalities and above all, the presence of mitochondrial abnormalities in the muscles, the brain and the tissues rich in energy, gave ground to the concept of mitochondrial encephalomyopathies. Then the nature of the dysfunctioning was assessed through biochemical studies, mainly the enzyme deficits of the respiratory chain mitochondria. But correlations between clinical and biochemical data were still difficult as these cases corresponded either to muscular damage (myalgia, exercise intolerance), either to various neurological alterations (epilepsy, cerebellar syndrome) or to multisystemic manifestations. Molecular biology technics introduced the notion of mitochondrial inheritance which contributed to underline the identity of certain varieties, mainly the Kearns and Sayre Syndrome. The increasing number of cases with mitochondrial abnormalities leads to the inverse approach: in central or peripheral damage of the nervous system or in very variable muscular alterations, the investigation of a mitochondrial dysfunctioning is justified and shows the way to possible therapies. This evolution of concept is remarkable in the history of medicine. An abnormality which, at first, was considered as an esthetic alteration, became the subject of the study which, through the advances of the clinical data, of the pathological anatomy, biochemistry and genetics, explained the mechanism of several alterations of the muscles and of the nervous system.