The prevalence and common clinical manifestations of the mitochondrial DNA 3243A > G mutation in children in a defined population in Finland were studied at the Universities of Oulu and Turku and other centers. Three probands were detected with encephalopathy, diabetes mellitus, or sensorineural hearing impairment, and 27 children as potential mutation carriers, with a prevalence of 18.4 in 100,000. Clinical features in 24 children in 5 families with 3243A > G mutation included migraine and learning disabilities, short stature, sensorineural hearing loss, exercise intolerance, delayed motor and speech development, and progressive encephalopathy. The prevalence was relatively high in the pediatric population, but morbidity in children is low, .
COMMENT. The 3243A > G mutation is the most common cause of the MELAS syndrome. Infants may present with the classic mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes while others show failure to thrive, hypotonia, seizures, cardiomyopathy, and lactic acidosis, dependent on the amount of mutant gene in different tissues. The clinical phenotype varies widely in symptoms and their severity. Many children with the 3243A > G mutation are asymptomatic, and those with symptoms usually present with sensorineural hearing loss, short stature, migraine, exercise intolerance, and learning difficulties. Encephalomyopathy is uncommon and morbidity relatively low.