Novel heteroplasmic mutation in the anticodon stem of mitochondrial tRNALys associated with dystonia and stroke-like episodes

Objectives - We report a novel heteroplasmic mitochondrial tRNALys mutation associated with dystonia, stroke-like episodes, sensorineural hearing loss and epilepsy in a Hungarian family. Material and methods - A 16-year-old boy, his brother and mother were investigated. Thorough clinical investigation as well as electrophysiological, neuroradiological and myopathological examinations were performed. Molecular studies included the analysis of the DYT1, DDP1/TIMM8A (deafness-dystonia peptid-1) genes and mitochondrial DNA (mtDNA). Results - The mtDNA analysis of the proband revealed a heteroplasmic A8332G substitution in the anticodon stem of the tRNALys gene. The mutation segregated in all affected family members. Besides this mutation 16 further mtDNA polymorphisms were detected. Complex I activity of the patient's fibroblast cultures showed decreased activity confirming mitochondrial dysfunction. Conclusion - The novel A8332G heteroplasmic mutation is most likely a new cause of dystonia and stroke-like episodes due to mitochondrial encephalopathy. The synergistic effect of the G8697A, A11812G and T10463C single nucleotide polymorphisms may modify the phenotype.