This study is performed by Eline Beert, PhD student in the lab for neurofibromatosis research, as part of achieving the degree of 'Doctor in Biomedical Sciences', with Prof. Dr. Eric Legius as promotor and main researcher. Only the Catholic University of Leuven and other foreign universities, but no commercial partners (like companies) will participate in this study. The results obtained from the described experiments have to be considered as pure scientific information and none will be reported to the patients.