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Homozygosity for the C9orf72 GGGGCC repeat expansion in frontotemporal dementia

Fratta, Pietro, Poulter, Mark, Lashley, Tammaryn, Rohrer, Jonathan D., Polke, James M., Beck, Jon, Ryan, Natalie, Hensman, Davina, Mizielinska, Sarah, Waite, Adrian James, Lai, Mang-Ching, Gendron, Tania F., Petrucelli, Leonard, Fisher, Elizabeth M. C., Revesz, Tamas, Warren, Jason D., Collinge, John, Isaacs, Adrian M. and Mead, Simon 2013. Homozygosity for the C9orf72 GGGGCC repeat expansion in frontotemporal dementia. Acta Neuropathologica 126 (3) , pp. 401-409. 10.1007/s00401-013-1147-0

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Abstract

An expanded hexanucleotide repeat in the C9orf72 gene is the most common genetic cause of frontotemporal dementia and amyotrophic lateral sclerosis (c9FTD/ALS). We now report the first description of a homozygous patient and compare it to a series of heterozygous cases. The patient developed early-onset frontotemporal dementia without additional features. Neuropathological analysis showed c9FTD/ALS characteristics, with abundant p62-positive inclusions in the frontal and temporal cortices, hippocampus and cerebellum, as well as less abundant TDP-43-positive inclusions. Overall, the clinical and pathological features were severe, but did not fall outside the usual disease spectrum. Quantification of C9orf72 transcript levels in post-mortem brain demonstrated expression of all known C9orf72 transcript variants, but at a reduced level. The pathogenic mechanisms by which the hexanucleotide repeat expansion causes disease are unclear and both gain- and loss-of-function mechanisms may play a role. Our data support a gain-of-function mechanism as pure homozygous loss of function would be expected to lead to a more severe, or completely different clinical phenotype to the one described here, which falls within the usual range. Our findings have implications for genetic counselling, highlighting the need to use genetic tests that distinguish C9orf72 homozygosity.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Medicine
MRC Centre for Neuropsychiatric Genetics and Genomics (CNGG)
Subjects: R Medicine > RC Internal medicine > RC0321 Neuroscience. Biological psychiatry. Neuropsychiatry
Uncontrolled Keywords: C9orf72; ALS; FTD
Publisher: Springer
ISSN: 0001-6322
Date of First Compliant Deposit: 30 March 2016
Last Modified: 04 Jun 2017 06:31
URI: http://orca-mwe.cf.ac.uk/id/eprint/61463

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