Overall cancer risk in people with deleterious germline <i>DDX41</i> variants

Germline loss-of-function (LoF) DDX41 variants predispose to late-onset hematopoietic malignancies (HM), predominantly of myeloid lineage. Among 43 families with germline DDX41LoF variants, bone marrow (BM) biopsies in those without (N=8) or with malignancies (N=21) revealed mild dysplasia in peripheral blood (57%) and BM (88%), long before the average age of DDX41-related HM onset. Therefore, we recommend baseline BM biopsies in people with germline DDX41LoF alleles to avoid over-diagnosis of myelodysplastic syndromes. A variety of solid tumors were also observed in our cohort, with 24% penetrance by age 75. Although acquired DDX41 mutations are common in HM, we failed to identify such alleles in solid tumors arising in those with germline DDX41LoF variants (N=15), suggesting an alternative mechanism driving solid tumor development. Furthermore, 33% of pedigrees in which ≥15% of first-degree relatives including the proband were diagnosed with a solid tumor had second germline deleterious variants in other cancer-predisposition genes, likely serving as primary cancer drivers. Finally, both lymphoblastoid cell lines and primary peripheral blood from individuals with germline DDX41LoF variants exhibited differential levels of inflammation-associated proteins. These data provide evidence of inflammatory dysfunction mediated by germline DDX41LoF alleles that may contribute to solid tumor growth in the context of additional germline cancer- associated variants. For those with HM and personal/family histories of solid tumors, we recommend broad germline testing. DDX41 may be an indirect modifier of solid tumor pathogenesis compared to its tumor suppressor function within hematopoietic tissues, a hypothesis that can be addressed in future work.