1 National Specialized Children's Hospital Okhmatdyt, Kyiv, Ukraine.
2 Department of Medical and Laboratory Genetics, National University PL Shupik, Kyiv, Ukraine.
3 MDUK Oxford Neuromuscular Centre and NIHR Oxford Biomedical Research Centre, University of Oxford, Oxford OX3 9DU, UK; Neuromuscular Reference Center, Department of Paediatrics, University Hospital of Liege and University of La Citadelle, Liege, Belgium. Electronic address: laurent.servais@paediatrics.ox.ac.uk.