1. Folkhälsan Research Center, Helsinki, Finland and Medicum, University of Helsinki , FI-00290 Helsinki , Finland
2. Klinik und Poliklinik für Neurologie, Sektion Neuromuskuläre Erkrankungen, Universitätsklinikum Bonn , D-53127 Bonn , Germany
3. Neuromuscular Research Center, Tampere University Hospital and Fimlab Laboratories , FI-33520 Tampere , Finland
4. Harry Perkins Institute of Medical Research, Centre for Medical Research, University of Western Australia , Nedlands WA , Australia