Germline DDX41 mutations define a unique subtype of myeloid neoplasms

: Germline DDX41 variants have been implicated in late-onset myeloid neoplasms (MNs). Despite an increasing number of publications, many important features of DDX41-mutated MNs remain to be elucidated. Here, enrolling a total of 346 patients with DDX41 pathogenic/likely pathogenic (P/LP) germline variants and/or somatic mutations from 9,082 MN patients, together with 525 first-degree relatives of DDX41-mutated and wild-type (WT) patients, we performed a comprehensive characterization of DDX41-mutated MNs. P/LP DDX41 germline variants explained ~80% of known germline predisposition to MNs in adults. These risk variants were 10-fold more enriched in Japanese MN cases (n=4,461) compared to a Japanese general population (n=20,238). This enrichment of DDX41 risk alleles was much more prominent in male than female (20.7 vs. 5.0). P/LP DDX41 variants conferred a large risk of developing MNs, which was negligible until 40 years old but rapidly increased to 49% by 90 years of age. DDX41-mutated MDS patients rapidly progressed to AML, which was, however, confined to those having truncating variants. Co-mutation patterns at diagnosis and at progression to AML were substantially different between DDX41-mutated and -WT cases, where none of the co-mutations affected clinical outcomes. Even TP53 mutations made no exceptions and their dismal effect, including multi-hit allelic status, on survival was almost completely mitigated by the presence of DDX41 mutations. Finally, outcomes were not affected by the conventional risk stratifications including the revised/molecular International Prognostic Scoring System (IPSS-R/M). Our findings establish that DDX41-mutated MDS defines a unique subtype of MNs that is distinct from other MNs.