RESUMEN
Mitochondrial cytopathies are diseases due to a defect of mitochondrial respiratory chain and are characterized by the presence of morphological abnormalities of mitochondria. These diseases may be due to alterations of the mitochondrial or the nuclear genome. The clinical manifestations can be polymorphic as various organs may be involved. We report the case of a 2-year-old boy who has a declined development correlated with a distal renal tubular acidosis. His behavioural and motor development was normal until l2months when a regression of his motor milestones with a pyramidal syndrome was noted. The metabolic investigation and the cranial MRI revealed a Leigh syndrome. The biochemical and immunological studies on biopsied skeletal muscle and cultured skin fibroblasts showed a deficiency in the complex IV respiratory chain [cytochrome c oxidase or COX]