Background and Aims: The natural course and severity of rating scale of mitochondrial myopathy, encephalopathy, lactic acidosis and stroke (MELAS) has not been clarified. The specific aim of the present study is to estimate the incidence, natural course and severity of the disease based on a Japanese cohort study.
Methods: Demography of MELAS is collected by questionnaire. The questionnaire was constructed based on Japanese mitochondrial disease rating scale. We analysed the age, symptoms of onset, survival rate and clinical progression of MELAS.
Results: We found 233 MELAS patients in Japan. There is a bimodal distribution in the onset of the disease. First symptoms were noted at the mean age of 9 years in juvenile and 32.2 years in the adult type. Death was described at a mean age of 15 years in juvenile and 40 years in the adult type. Convulsion, stroke-like episodes, headache and muscle weakness were the most frequent first symptoms in both forms. Using the Japanese mitochondrial disorders rating scale, juvenile type showed a rapid increase of their exacerbation within 5–9 years after the onset of disease. Using Kaplan–Meier survival analysis, juvenile type has 3.2 times more chance of death than those with the adult type. Seventy eight per cent of MELAS has an A3243G mutation and all showed abnormality in muscle biopsy. l-Arginine therapy may improve the progression of the disease in the entire course.
Conclusions: MELAS, the most commen mitochondrial disorder, shows vascular dementia in the progressive stage and turns out to be a rapidly progressive degenerating disorder in Japan. l-Arginine therapy is a good candidate for a clinical trial on MELAS.