Background: The number of molecular causes of MELAS (a syndrome consisting of mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes) and Leigh syndrome (LS) has steadily increased. Among these, mutations in the ND5 gene (OMIM 516005) of mitochondrial DNA are important, and the A13513A change has emerged as a hotspot.
Objective: To describe the clinical features, muscle pathological and biochemical characteristics, and molecular study findings of 12 patients harboring the G13513A mutation in the ND5 gene of mitochondrial DNA compared with 14 previously described patients with the same mutation.
Design: Clinical examinations and morphological, biochemical, and molecular analyses.
Setting: Tertiary care university hospital and molecular diagnostic laboratory.
Patients: Three patients had the typical syndrome features of MELAS; the other 9 had typical clinical and radiological features of LS.
Results: Family history suggested maternal inheritance in a few cases; morphological studies of muscle samples rarely showed typical ragged-red fibers and more often exhibited strongly succinate dehydrogenase-reactive blood vessels. Biochemically, complex I deficiency was inconsistent and generally mild. The mutation load was relatively high in the muscle and blood specimens.
Conclusion: The G13513A mutation is a common cause of MELAS and LS, even in the absence of obvious maternal inheritance, pathological findings in muscle, or severe complex I deficiency.