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Abstract For most patients with childhood myelodysplastic syndrome (cMDS), allogeneic hematopoietic stem cell transplantation (allo‐HSCT) remains the only curative option. In the case of increased blasts (cMDS‐IB), the benefit of pretransplant cytoreductive therapy remains controversial. In this multicenter retrospective study, the outcomes of all French children who underwent allo‐HSCT for cMDS reported in the SFGM‐TC registry between 2000 and 2020 were analyzed (n = 84). The median age at transplantation was 10.2 years. HSCT was performed from matched sibling donors (MSD) in 29% of the cases, matched unrelated donors (MUD) in 44%, haploidentical in 6%, and cord blood in 21%. Myeloablative conditioning was used in 91% of cases. Forty‐eight percent of patients presented with cMDS‐IB at diagnosis (median BM blasts: 8%). Among them, 50% received pretransplant cytoreductive therapy. Five‐year overall survival (OS), cumulative incidence of nonrelapse mortality (NRM), and relapse were 67%, 26%, and 12%, respectively. Six‐month cumulative incidence of grade II–IV acute graft‐versus‐host disease was 46%. Considering the whole cohort, age under 12, busulfan/cyclophosphamide/melphalan conditioning or MUD were associated with poorer 5‐year OS. In the cMDS‐IB subgroup, pretransplant cytoreductive therapy was associated with a better OS in univariate analysis. This seems to be mainly due to a decreased NRM since no impact on the incidence of relapse was observed. Overall, those data may argue in favor of cytoreduction for cMDS‐IB. They need to be confirmed on a larger scale and prospectively.

Abstract Context Mucopolysaccharidosis (MPS) requires urgent treatment to prevent neurological damage. While gene therapy holds promise for effectively treating these diseases with minimal toxicity, access remains limited for most patients. Consequently, advancing allogeneic hematopoietic stem cell transplantation (HSCT) for young children is crucial. Since the 2010s, cord blood (CB) transplants with reduced‐toxicity conditioning (RTC) have become the standard of care. Patients and methods Recent reports in France indicate a significant incidence of graft failures (GF), prompting a large‐scale retrospective study from the French‐speaking bone marrow transplantation society's registry, to understand GF risks, guide clinicians in selecting transplant platforms, and describe outcomes of second HSCT in young patients. Results This report analyses 93 children who underwent HSCT for MPS between 2000 and 2020. The GF rate was notably high (22.6% at day 100), primarily associated with the donor's HLA compatibility and the recipient's age. Well‐matched CB and RTC were not found to be risk factors for GF. This study also details the procedures for second and third transplants in patients who rejected their first HSCT. Conclusion In the era of RTC, CB remains a viable and expedient option for MPS transplantation.