MDM4-related bone marrow failure

We report 6 unrelated individuals with variable BMF phenotypes and hypocellular MDS. The median age at presentation was 10 years (4 weeks - 53 years). Unbiased genomic analysis revealed germline heterozygous variants in MDM4, including 4 null (frameshift, nonsense, and splice-site resulting in premature truncation confirmed by RNA sequencing) and 2 missense variants. Mechanistically, MDM4 mutations lead to loss-of-function with enhanced p53 activation. We used CRISPR/Cas9 to delete MDM4 in healthy donor hematopoietic stem and progenitor cells (HSPCs). The resulting MDM4-haploinsufficient HSPCs exhibited increased p53 activity, impaired colony-forming capacity, and reduced engraftment potential in immunodeficient mice. Complementation studies revealed the functional necessity of both p53-binding and RING-finger domains in MDM4-mediated hematopoietic regulation. To study variant effect in a genetic background free of potential confounders, we introduced patient-specific MDM4 variants into induced pluripotent stem cells (iPSCs). MDM4-mutant iPSCs yielded significantly reduced erythroid and myeloid cell populations and exhibited increased p53 activity, as evidenced by elevated p21 expression, confirming the role of MDM4 in regulating hematopoiesis through p53 modulation. Transcriptome analysis of iPSC-derived hematopoietic cells revealed upregulation of p53 pathway. Importantly, one patient acquired TP53 mutations, suggesting clonal rescue in the context of MDM4 deficiency. Our findings establish MDM4 deficiency as a new “TP53-opathy” BMF syndrome with variable hematopoietic manifestations. This study also highlights the critical role of the MDM4-p53 axis in maintaining hematopoietic homeostasis.