Huntington disease is caused by a CAG repeat expansion in the huntingtin gene. A repeat length of 35 CAGs has long been accepted as the cut-off point beyond which the expansion becomes pathological, but recent findings indicate that intermediate expansions (27–35 repeats) are associated with either a distinct behavioural phenotype or an endophenotype.
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Acknowledgements
F. Squitieri gratefully thanks patients and associated family members at Lega Italiana Ricerca Huntington and Related Diseases (http://www.lirh.it) for their continued support, and Dr Alba Di Pardo for her comments and technical support on the figure.
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Squitieri, F. 'Fifty shades of grey' in the Huntington disease gene. Nat Rev Neurol 9, 421–422 (2013). https://doi.org/10.1038/nrneurol.2013.128
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DOI: https://doi.org/10.1038/nrneurol.2013.128
