CONCORDANCE OF SOMATIC GENETIC TESTING IN BLOOD VS. BONE MARROW IN SHWACHMAN-DIAMOND SYNDROME

Methods: We performed single-cell multimodal sequencing of RNA and surface proteins on diagnostic BM aspirates from pMDS-RCC patients without genetic predisposition (n=6; ages 9-17) and age-matched healthy controls (n=4).Samples were FACS-enriched for hematopoietic stem and progenitor cells (HSPCs) and mesenchymal stromal cells (MSCs), alongside non-enriched fractions.Spatial transcriptomics was performed on trephine biopsies from pMDS-RCC patients (n=4; ages 9-16 years) and non-cancerous controls (n=10; ages 1-17).Results: We profiled 44,747 cells from pMDS-RCC patients and 40,400 cells from controls.Comparative analysis revealed reduced HSPCs and myeloid populations in pMDS-RCC, with increased frequencies of T-cell populations, except for regulatory T-cells.There was no difference in T-cell activation markers, indicating an absence of an inflammatory state.Cell cycle analysis showed more HSPCs in the G2M phase in pMDS-RCC, consistent with impaired differentiation and cell cycle arrest.This was accompanied by downregulation of key HSPC maintenance genes (e.g.AREG, SRGN) and a loss of HSPC-MSC interactions (e.g.KIT-KITL).Spatial transcriptomics analysis (42,073 cells) confirmed a disorganized BM microenvironment with disrupted spatial relationships between HSPCs, MSCs and immune cells. Conclusion:This study provides a detailed single-cell overview of pMDS-RCC BM, revealing a dysfunctional niche that impairs HSPC maintenance and lineage commitment, driving ineffective hematopoiesis and immune imbalance in pMDS-RCC patients.