Footnotes

• Contributors JCS wrote the initial manuscript and contributed to the analysis and interpretation of data. SMM, ID, RP, GA, SN, FB, PG and MMR contributed to drafting and rewriting the initial manuscript as well as to the analysis and interpretation of data. All authors give approval for publication. PG and MMR contributed equally to this manuscript.

• Funding This work was supported by the National Institutes of Neurological Diseases and Stroke and office of Rare Diseases, Grant number U54NS065712 (to SMM, MMR), Ataxia UK (SN, PG) the Medical Research Council and the Muscular Dystrophy Campaign (MMR).

• Competing interests SMM has received support for her research from the National Institutes of Neurological Diseases and Stroke and office of Rare Diseases (U54NS065712). SN has received research grant funding from Ataxia UK. PG has received research grant funding from Ataxia UK. MMR serves on the editorial boards of the Journal of Neurology, Neurosurgery and Psychiatry, Neuromuscular Disorders and the Journal of the Peripheral Nervous System and on the editorial advisory board of Brain. MMR is grateful to the Medical Research Council (MRC) and the National Institutes of Neurological Diseases and Stroke and office of Rare Diseases (U54NS065712) for their support. This work was undertaken at University College London Hospitals/University College London, which received a proportion of funding from the Department of Health's National Institute for Health Research Biomedical Research Centres funding scheme.

• Provenance and peer review Not commissioned; externally peer reviewed.