1 Department of Paediatrics, University of Cologne, 50924 Cologne, Germany. Electronic address: anne.koy@uk-koeln.de.
2 Evelina Children's Hospital, Guy's and St Thomas' NHS Foundation Trust, London, UK.
3 University of Southern California, Los Angeles, CA, USA.
4 Cook Children's Medical Center, Fort Worth, TX, USA.
5 University of Rochester Medical Center, Rochester, NY, USA.
6 Department of Neurology, University of Cologne, 50924 Cologne, Germany; Department of Neurology, University of Giessen and Marburg, 35043 Marburg, Germany.