In summary, the primary goal of this study is to evaluate the Treosulfan-based myeloablative conditioning regimen as an alternative in children and to contribute to the current PK model for Treosulfan to be able to finally give age (or body surface area [BSA]) dependent dose recommendations. The treatment regimens given in the protocol MC-FludT.16/NM are based on sufficient clinical safety and efficacy data. Considering the vital indication for allogeneic HSCT of the selected patient population, the risk-benefit assessment seems to be in favour of the study conduct.