Mitochondrial myopathy associated with sudden death in young adults and a novel mutation in the mitochondrial DNA leucine transfer RNA(UUR) gene.

A family exhibited maternal inheritance of a variable syndrome comprising ocular, neck and proximal upper limb weakness, psychiatric features, and sudden death. Of 15 definitely or probably affected individuals, 7 had died in early adult life, probably of respiratory failure. A novel point mutation of mitochondrial DNA, in a transfer RNA gene at position 3251, was detected in all living affected family members.