We sequenced the mitochondrial genome from a 40-year-old woman with myoclonus epilepsy, retinitis pigmentosa, leukoencephalopathy and cerebral calcifications. Histological and biochemical features of mitochondrial respiratory chain dysfunction were present. Direct sequencing showed a novel hetero-plasmic mutation at nucleotide 5513 in the MT-TW gene that encodes tRNA(TrP). Restriction Fragment Length Polymorphism analysis confirmed that about 80% of muscle mtDNA harboured the mutation while it was present in minor percentages in mtDNA from other tissues. The mutation is predicted to disrupt a highly conserved base pair within the aminoacyl acceptor stem of the tRNA. This is the 17 mutation in MT-TW gene and expands the known causes of late-onset mitochondrial diseases. (C) 2018 Elsevier Inc. All rights reserved.