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Mitochondrial myopathy, Encephalopathy, Lactic Acidosis, and Stroke-like episodes (MELAS) is a rare mitochondrial disorder. Diagnostic criteria for MELAS include typical manifestations of the disease: stroke-like episodes, encephalopathy, evidence of mitochondrial dysfunction (laboratorial or histological) and known mitochondrial DNA gene mutations. Clinical features of MELAS are not necessarily uniform in the early stages of the disease, and correlations between clinical manifestations and physiopathology have not been fully elucidated. It is estimated that point mutations in the tRNALeu(UUR) gene of the DNAmt, mainly A3243G, are responsible for more of 80% of MELAS cases. Morphological changes seen upon muscle biopsy in MELAS include a substantive proportion of ragged red fibers (RRF) and the presence of vessels with a strong reaction for succinate dehydrogenase. In this review, we discuss mainly diagnostic criterion, clinical and laboratory manifestations, brain images, histology and molecular findings as well as some differential diagnoses and current treatments.

ObjectiveTo identify the molecular basis and elucidate the pathogenesis of a fatal congenital myasthenic syndrome.MethodsWe performed clinical electrophysiology studies, exome and Sanger sequencing, and analyzed functional consequences of the identified mutation.ResultsClinical electrophysiology studies of the patient revealed several‐fold potentiation of the evoked muscle action potential by high frequency nerve stimulation pointing to a presynaptic defect. Exome sequencing identified a homozygous c.340delA frameshift mutation in synaptobrevin 1 (SYB1), one of the three SNARE proteins essential for synaptic vesicle exocytosis. Analysis of both human spinal cord gray matter and normal human muscle revealed expression of the SYB1A and SYB1D isoforms, predicting expression of one or both isoforms in the motor nerve terminal. The identified mutation elongates the intravesicular C‐terminus of the A isoform from 5 to 71, and of the D isoform from 4 to 31 residues. Transfection of either mutant isoform into bovine chromaffin cells markedly reduces depolarization‐evoked exocytosis, and transfection of either mutant isoform into HEK cells significantly decreases expression of either mutant compared to wild type.InterpretationThe mutation is pathogenic because elongation of the intravesicular C‐terminus of the A and D isoforms increases the energy required to move their C‐terminus into the synaptic vesicle membrane, a key step for fusion of the synaptic vesicle with the presynaptic membrane, and because it is predicted to reduce expression of either isoform in the nerve terminal.

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Pompe disease (PD) can be diagnosed by measuring alpha-glucosidase levels or by identifying mutations in the gene enzyme. Muscle biopsies can aid diagnosis in doubtful cases.Methods:A review of muscle biopsy from 19 cases of PD (infantile, 6 cases; childhood, 4 cases; and juvenile/adult, 9 cases).Results:Vacuoles with or without glycogen storage were found in 18 cases. All cases had increased acid phosphatase activity. The vacuole frequency varied (almost all fibers in the infantile form to only a few in the juvenile/adult form). Atrophy of type 1 and 2 fibers was frequent in all forms. Atrophic angular fibers in the NADH-tetrazolium reductase and nonspecific esterase activity were observed in 4/9 of the juvenile/adult cases.Conclusion:Increased acid phosphatase activity and vacuoles were the primary findings. Most vacuoles were filled with glycogen, and the adult form of the disease had fewer fibers with vacuoles than the infantile or childhood forms.

In this review, we discuss the therapies used in the treatment of patients with Duchenne muscular dystrophy since the first description of the disease. A short description is given of the various theories based on disease pathogenesis, which give the substrates for the many therapeutic interventions. A brief review of the methods of evaluation used in therapeutic trials is made. Of all the treatments, the only drugs that are still considered able to modify the course of the disease are the corticosteroids (prednisone/prednisolone/deflazacort). Other drugs (coenzyme Q10 and creatine) have had a little effect in a few functions without adverse reactions. Idebenone seems to improve the respiratory function in the long term. The trials with mRNA transcription, through nonsense mutations or exon 51 skipping, show some beneficial results in a few functional tests, but they are limited to a small set of DMD patients.