The aim of the trial is to describe the safety and efficacy of intravenous (i.v.) Treosulfan compared to the conventional (myeloablative) dose of i.v. Busulfan, each administered as part of a standardised Fludarabine-containing conditioning regimen and to contribute to a PK model which permits - in conjunction with data comparing Treosulfan and Busulfan in adults with malignant diseases - to extend the use of Treosulfan in the paediatric population by extrapolating efficacy.

The prospective clinical phase II protocol MC-FludT.16/NM is to be conducted to verify safety and efficacy of Treosulfan-based conditioning compared to Busulfan-based conditioning in paediatric patients. Based on the given clinical experience with either Treosulfan-based or Busulfan-based conditioning in combination with Fludarabine no increased risk for graft failure is expected in paediatric patients. A potential benefit for study patients is expected with respect to a probably low non-haematological toxicity of treatment compared to myeloablative TBI-based conditioning or high-dose Busulfan-based conditioning in combination with Cyclophosphamide.

However, the allogeneic HSCT procedure itself potentially involves serious risks with regard to severe or life-threatening conditions like graft versus host disease (GvHD) and/or infectious complications as well as graft failure.

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.

Moreover, planned interim analyses will ensure the early identification of unexpected risks. Therefore, the conduct of the protocol MC-FludT.16/NM is considered reasonably justified.

Inclusion Criteria:

1. Non-malignant disease indicated for first myeloablative allogeneic HSCT, including inborn errors of metabolism, primary immunodeficiencies, haemoglobinopathies and bone marrow failure syndromes.
2. First allogeneic HSCT.
3. Available matched sibling donor (MSD), matched family donor (MFD) or matched unrelated donor (MUD). For bone marrow (BM) and peripheral blood (PB) match is defined as at least 9/10 allele matches after four digit typing in human leucocyte antigen (HLA)-A, -B, -C, -DRB1 and DQB1 antigens. For umbilical cord blood (UCB) match is defined as at least 5/6 matches after two digit typing in HLA-A and -B and four digit typing in DRB1 antigens.

Exclusion Criteria:

1. Second or later HSCT.
2. HSCT from mismatched donor (less than 9/10 BM/peripheral blood stem cells (PBSC) or less than 5/6 matched cord donor).
3. Preterm newborn infants (<37 weeks gestational age) and term newborn infants aged 0 - 27 days at time of registration.
4. Obese paediatric patients with body mass index weight (kg)/[height (m)]² > 30 kg/m².
5. Diagnosis of Fanconi anaemia and other chromosomal breakage disorders, radiosensitivity disorders (deoxyribonucleic acid (DNA) Ligase 4, Cernunnos- X-ray repair cross-complementing protein 4 (XRCC4) like factor (XLF), Nijmegen Breakage Syndrome (NBS)) and Dyskeratosis Congenita.