[1] Univ London Imperial Coll Sci Technol & Med, London SW7 2AZ, England
[2] Royal Brompton & Harefield NHS Fdn Trust, London, England
[3] Northern Ireland Reg Genet Serv, Belfast, Antrim, North Ireland
[4] Queen Elizabeth Univ Hosp, Lab Med, Dept Clin Genet, Glasgow, Lanark, Scotland
[5] Wellcome Trust Ctr Mitochondrial Res, Newcastle Upon Tyne, Tyne & Wear, England