[Mitochondrial diseases--more common than we realize?].

: The last two decades have revealed a novel group of inborn errors with defects on the pathways of aerobic energy substrates into the mitochondria or the capacity to generate reducing potential from these substrates, as well as those that block the oxidative phosphorylation pathway itself. The mitochondrial diseases are clinically heterogenous disorders that can affect multiple organ systems, mainly the skeletal muscle and nervous system (mitochondrial encephalomyopathies). There are a few distinctive syndromes such as Leigh's syndrome, Alper's syndrome, Kearns-Sayre's syndrome, myoclonus epilepsy with "ragged-red fibres" (MERRF), and MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, strokelike episodes). The last year our department has evaluated ten children with mitochondrial disorders. Among these are two siblings with Leigh's syndrome and cytochrome c-oxidase defect. The first child, a girl, developed the first symptoms at the age of four months and died 13 months old. The younger brother showed the same clinical picture as his sister. However, the clinical neurological picture was stabilized when he was 18 months old, and he is still alive at six years of age and slightly psychomotorically retarded.