1. Wellcome Trust Mitochondrial Research Centre and the John Walton Muscular Dystrophy Research Centre, Institute of Genetic Medicine, Newcastle University, Central Parkway, Newcastle upon Tyne, UK
2. Present address: Department of Clinical Neurosciences, Cambridge and MRC Mitochondrial Biology Unit, University of Cambridge, Cambridge, UK
3. Newcastle Eye Centre, Royal Victoria Infirmary, Newcastle upon Tyne, UK
4. NIHR Biomedical Research Centre at Moorfields Eye Hospital and UCL Institute of Ophthalmology, London, UK