Molecular Genetics and Metabolism 84 (2005) 176–188 www.elsevier.com/locate/ymgme 1096-7192/$ - see front matter  2004 Elsevier Inc. All rights reserved. doi:10.1016/j.ymgme.2004.10.003 Contrasting phenotypes in three patients with novel mutations in mitochondrial tRNA genes Roberto Anitori a,1 , Kara Manning a , Franklin Quan a , Richard G. Weleber b , Neil R.M. Buist c , Eric A. Shoubridge d , Nancy G. Kennaway a,¤ a Department of Molecular and Medical Genetics, Oregon Health & Science University, Portland, OR 97239, USA b Department of Molecular and Medical Genetics and the Casey Eye Institute, Oregon Health & Science University, Portland, OR 97239, USA c Departments of Pediatrics and Molecular and Medical Genetics, Oregon Health & Science University, Portland, OR 97239, USA d The Montreal Neurological Institute, McGill University, Montreal, Que., Canada Received 29 July 2004; received in revised form 1 October 2004; accepted 2 October 2004 Available online 15 December 2004 Abstract We studied three patients, each harboring a novel mutation at a highly conserved position in a diVerent mitochondrial tRNA gene. The mutation in patient 1 (T5543C) was associated with isolated mitochondrial myopathy, and occurred in the anticodon loop of tRNA Trp . In patient 2, with mitochondrial myopathy and marked retinopathy, the mutation (G14710A) resulted in an anticodon swap (Glu to Lys) in tRNA Glu . Patient 3, who manifested mitochondrial encephalomyopathy and moderate retinal dysfunction, har- bored a mutation (C3287A) in the TC loop of tRNA Leu(UUR) . The mutations were heteroplasmic in muscle in all cases, and sporadic in two cases. PCR-RFLP analysis in all patients showed much higher amounts of mutated mtDNA in aVected tissue (muscle) than unaVected tissue (blood), and signiWcantly higher levels of mutated mtDNA in cytochrome c oxidase (COX)-negative muscle Wbers than in COX-positive Wbers, conWrming the pathogenicity of these mutations. The mutation was also detected in single hair roots from all three patients, indicating that each mutation must have arisen early in embryonic development or in maternal germ cells. This suggests that individual hair root analyses may reXect a wider tissue distribution of mutated mtDNA than is clinically apparent, and might be useful in predicting prognosis and, perhaps, the risk of transmitting the mutation to oVspring. Our data suggest a corre- lation between clinical phenotype and distribution of mutated mtDNA in muscle versus hair roots. Furthermore, the high threshold for phenotypic expression in single muscle Wbers (92–96%) suggests that therapies may only need to increase the percentage of wild- type mtDNA by a small amount to be beneWcial.  2004 Elsevier Inc. All rights reserved. Keywords: Mitochondrial myopathy; Mitochondrial encephalomyopathy; Pigmentary retinopathy; Mitochondrial DNA; Mitochondrial tRNA mutation; Complex I deWciency; Complex IV deWciency; Cytochrome c oxidase negative Wbers; Hair root analysis; Pathogenesis of mitochondrial tRNA mutations Introduction The mitochondrial myopathies and encephalomy- opathies (MIM251900) encompass a diverse group of disorders of mitochondrial function, frequently associ- ated with defects of the respiratory chain [1,2]. The diversity of these disorders reXects not only the com- plexity of the respiratory chain itself, made up of >80 individual proteins that are organized into Wve major complexes (I–V), but also the unique properties of mtDNA which encodes 13 of these polypeptides: 7 (ND1-6 and 4L) in complex I (NADH:ubiquinone oxi- doreductase; EC 1.6.5.3.); 1 (cytochrome b) in complex * Corresponding author. Fax: +1 503 494 7645. E-mail address: kennaway@ohsu.edu (N.G. Kennaway). 1 Present address: Australian Centre for Astrobiology, Macquarie University, North Ryde, 2109, NSW, Australia.