• Laura E Downey, Phillip D Fletcher, Hannah L Golden, Colin J Mahoney, Jennifer L Agustus, Jonathan M Schott, Jonathan D Rohrer, Jonathan Beck, Simon Mead, Martin N Rossor, Sebastian J Crutch, and Jason D Warren.
• Department of Neurodegenerative Disease, Dementia Research Centre, UCL Institute of Neurology, University College London, London, UK.
• J. Neurol. Neurosurg. Psychiatr. 2014 Sep 1; 85 (9): 101610231016-23.

BackgroundMutations in C9ORF72 are an important cause of frontotemporal dementia (FTD) and motor neuron disease. Accumulating evidence suggests that FTD associated with C9ORF72 mutations (C9ORF72-FTD) is distinguished clinically by early prominent neuropsychiatric features that might collectively reflect deranged body schema processing. However, the pathophysiology of C9ORF72-FTD has not been elucidated.MethodsWe undertook a detailed neurophysiological investigation of five patients with C9ORF72-FTD, in relation to patients with FTD occurring sporadically and on the basis of mutations in the microtubule-associated protein tau gene and healthy older individuals. We designed or adapted behavioural tasks systematically to assess aspects of somatosensory body schema processing (tactile discrimination, proprioceptive and body part illusions and self/non-self differentiation).ResultsPatients with C9ORF72-FTD selectively exhibited deficits at these levels of body schema processing in relation to healthy individuals and other patients with FTD.ConclusionsAltered body schema processing is a novel, generic pathophysiological mechanism that may link the distributed cortico-subcortical network previously implicated in C9ORF72-FTD with a wide range of neuropsychiatric and behavioural symptoms, and constitute a physiological marker of this neurodegenerative proteinopathy.Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

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