The authors are also grateful to Prof. Dr. Koen Luyckx for statistical advice, Dr. Hugo Vanderstichele and Fujirebio Europe NV for practical and logistic help with collecting and analyzing the CSF samples, Prof. Dr. Jan Cools and Nicole Menten for their assistance in MTHFR genotyping and the pediatric oncology team for their dedicated care for childhood-cancer patients. Here, MTHFR is linked to cancer.