Objective FUS gene mutations were recently identified in familial amyotrophic lateral sclerosis (ALS). The present studies sought to define the clinical, post-mortem and neurophysiological phenotypes in ALS families with FUS mutations and to determine the frequency of FUS mutations in familial and sporadic ALS.
Methods FUS was screened for mutations in familial and sporadic ALS cases. Clinical, post-mortem and neurophysiological features of large families with FUS mutations are described.
Results and conclusions FUS mutations were evident in 3.2% (4/124) of familial ALS, representing the second most common gene abnormality to be described in familial ALS after SOD1. No mutations were present in 247 sporadic ALS cases. The clinical presentation in 49 affected patients was consistent with a predominantly lower motor neuron disorder, supported by post-mortem findings. Upper motor neuron involvement varied, with Wallerian degeneration of corticospinal tracts present in one post-mortem case but absent in a second case from the same family. Features of cortical hyperexcitability demonstrated upper motor neuron involvement consistent with other forms of familial and sporadic ALS. One case presented with frontotemporal dementia (FTD) indicating that this may be a rare presenting feature in families with FUS mutation. Ubiquitin-positive cytoplasmic skein-like inclusions were present in lower motor neurons, but in contrast to sporadic ALS, no TDP-43 pathology was evident. Mutation-specific clinical features were identified. Patients with a R521C mutation were significantly more likely to develop disease at a younger age, and dropped-head syndrome was a frequent feature. Reduced disease penetrance was evident among most affected families.
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Funding This work was supported by the Peter Stearne grant for familial MND from the Motor Neurone Disease Research Institute of Australia (MNDRIA), a Clinical Fellowship to SV from the MNDRIA, the Stephen Buckley motor neuron disease research grant from Australian Rotary Health, a National Health and Medical Research Council of Australia (NHMRC) Career Development Award (511941) to IPB, and project grants (510233 and 570957) from the NHMRC of Australia.
Competing interests None.
Patient consent Obtained.
Ethics approval Ethics approval was provided by the Sydney South West Area Health Service, Sydney, Australia.
Provenance and peer review Not commissioned; externally peer reviewed.
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