RNA therapy for polyglutamine neurodegenerative diseases Lauren M. Watson 1,2 and Matthew J. A. Wood 1, * Polyglutamine neurodegenerative diseases result from the expansion of a trinucleotide CAG repeat, encoding a polyglutamine tract in the disease- causing protein. The process by which each polyglutamine protein exerts its toxicity is complex, involving a variety of mechanisms including transcriptional dysregulation, proteasome impairment and mitochondrial dysfunction. Thus, the most effective and widely applicable therapies are likely to be those designed to eliminate production of the mutant protein upstream of these deleterious effects. RNA-based approaches represent promising therapeutic strategies for polyglutamine diseases, offering the potential to suppress gene expression in a sequence-specific manner at the transcriptional and post- transcriptional levels. In particular, gene silencing therapies capable of discrimination between mutant and wildtype alleles, based on disease-linked polymorphisms or CAG repeat length, might prove crucial in cases where a loss of wild type function is deleterious. Novel methods, such as gene knockdown and replacement, seek to eliminate the technical difficulties associated with allele-specific silencing by avoiding the need to target specific mutations. With a variety of RNA technologies currently being developed to target multiple facets of polyglutamine pathogenesis, the emergence of an effective therapy seems imminent. However, numerous technical obstacles associated with design, discrimination and delivery must be overcome before RNA therapy can be effectively applied in the clinical setting. Neurodegenerative diseases represent a significant proportion of the noncommunicable disease burden in developed countries, for which few treatment options are available. A subset of these conditions, collectively known as polyglutamine (polyQ) diseases, have a well- defined genetic aetiology, making them attractive targets for gene-based therapies. There are currently nine known inherited polyQ diseases: Huntington’ s disease (HD), 1 Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK 2 Division of Human Genetics, Institute of Infectious Disease and Molecular Medicine, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa *Corresponding author: Matthew J. A. Wood, Department of Physiology, Anatomy and Genetics, University of Oxford, South Parks Road, Oxford OX1 3QX, UK. E-mail: matthew.wood@dpag.ox. ac.uk expert reviews http://www.expertreviews.org/ in molecular medicine 1 Accession information: doi:10.1017/erm.2011.1; Vol. 14; e3; January 2012 © Cambridge University Press 2012 RNA therapy for polyglutamine neurodegenerative diseases