Myelodysplastic syndrome with dual germline RUNX1 and DDX41 variants: a rare genetic predisposition case.

Germline variants in RUNX1 and DDX41 are well-established contributors to hereditary myeloid neoplasms and are increasingly recognized as critical predisposing factors in the developing myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). This case report details a 51-year-old male diagnosed with MDS with excess blasts-1 (MDS-EB1), who harbored a rare combination of pathogenic germline variants in RUNX1 and a novel potentially pathogenic variant in DDX41 variant, alongside a somatic DDX41 mutation. The coexistence of these germline variants highlights the genetic complexity underlying hereditary myeloid neoplasms and reinforces the necessity of comprehensive genomic testing to ensure accurate diagnosis and informed clinical management. The interplay between RUNX1 and DDX41 variants may drive leukemogenesis, with the germline RUNX1 variant potentially fostering a cellular environment that enables the acquisition of somatic DDX41 mutations, leading to hematological malignancies. Conversely, the germline DDX41 variant may disrupt hematopoiesis and, when combined with RUNX1 dysfunction, contribute to disease progression. This case underscores the importance of screening germline variants in patients with myeloid neoplasms. It emphasizes the need to confirm the origin of these variants in non-hematopoietic tissues, such as fibroblasts (gold standard), to avoid misinterpretation caused by clonal hematopoiesis. Further research is warranted to elucidate the molecular mechanisms driving the interaction between RUNX1 and DDX41 variants and their collective impact on disease progression, treatment outcomes, and familial risk.