[Benign congenital myopathy associated with a partial deficiency of complexes I and III of the mitochondrial respiratory chain]].

INTRODUCTION: Isolated or combined enzyme deficiencies of the mitochondrial respiratory chain results in a number of clinical heterogeneous conditions. When presented in the neonatal period or early in the infancy the course is usually severe, although isolated cases with benign evolution have also been described.

OBJECTIVE: To describe the clinical and biochemical characteristics of a child with a benign form of mitochondrial myopathy due to a combined deficiency of the complexes I and III of the respiratory chain.

CLINICAL CASE: A 40 days-old male, the second son of a young non-consanguineous couple, presented with axial congenital hypotonia, asymmetrical macrocephaly, mild enlargement of the liver, mild coarsening of facial features, increased CK serum values, persistently elevation of serum lactate and lactate/pyruvate ratio and external hydrocephalus. Electromyogram and histological muscle examination were normal but analysis of the respiratory chain disclosed a deficiency of the complexes I and III. From 13 months-age onwards clinical detailed abnormalities progressively ameliorated and also did it serum CK, lactate and external hydrocephalus.

CONCLUSION: We think that on clinical, basic biochemical and histological grounds there are some similarities between this case of congenital unspecific myopathy and benign reversible form of mitochondrial myopathy, arguing in favor of a possible relationship between both conditions.