1. Neurology Department, Institute of Neurological Sciences, Queen Elizabeth University Hospital, Glasgow G51 4TF, UK
2. Genetics Department, West Scotland Regional Genetics Service, Queen Elizabeth University Hospital, Glasgow G51 4TF, UK
3. Wellcome Trust Centre for Mitochondrial Research, Newcastle University, Newcastle-upon-Tyne, UK
4. Department of Geographical and Earth Sciences, University of Glasgow, Glasgow, G20 8QQ, UK