Slowly progressive encephalopathy with hearing loss due to a mutation in the mtDNA tRNA(Leu(CUN)) gene.

Pathogenic mutations in the tRNA(Leu(UCN)) gene of mitochondrial DNA (mtDNA) have been invariably accompanied by skeletal myopathy with or without chronic progressive external ophthalmoplegia (CPEO). We report a young woman with a heteroplasmic m.12276G>A mutation in tRNA(Leu(UCN)), who had childhood-onset and slowly progressive encephalopathy with ataxia, cognitive impairment, and hearing loss. Sequencing of the 22 tRNA mitochondrial genes is indicated in all unusual neurological syndromes, even in the absence of maternal inheritance.