Welcome to the MDS 2023 Congress Calendar

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DDX41, located on the long arm of chromosome 5 (5q35.3), encodes a DEAD-box helicase family protein that is essential for cell growth and viability. The precise function of DDX41 is unknown, but several studies suggested its activities in RNA splicing, processing pathways, and myeloid differentiation.

DDX41 germline mutations (DDX41MutGl) are the most common genetic predisposition to myeloid malignancies, including myelodysplastic syndrome (MDS). They represent 5% of patients with a diagnosis of acute myeloid leukemia (AML) and might represent 5 to 10% of MDS patients. Although family history of hematological malignancy is highly suggestive of germline predisposition including DDX41MutGl, we and others founded that most patients with DDX41MutGl MDS/AML at diagnosis didn’t report any family history. These observations are in line with a more recent report on DDX41MutGl penetrance in Japanese population, which founded an approximately 50% lifetime risk of leukemia in DDX41MutGl relatives.

DDX41MutGl patients are mostly male, in their seventh decade. Accordingly, penetrance associated with DDX41MutGl is significantly higher in male than female, the risk of myeloid malignancy being almost negligible before 40 years. Male sex skewing and older age of hematological disease onset are specific patterns associated to DDX41 predisposition and contrast with other MDS/AML predisposition syndromes that mostly arise in children and young adults (SAMD9/SAMD9LMutGl, RUNX1MutGl or GATA2MutGl).

In comparison with other sporadic MDS/AML, DDX41MutGl patients have bone marrow blast infiltration between 10 to 35%, low leukocyte count, normal cytogenetics and few of the additional somatic mutations frequently associated with myeloid malignancies.

The most frequent somatic alteration detected in bone marrow DDX41MutGl patients is a second DDX41 mutation (DDX41MutSom), which was reported in several large studies in more than half of DDX41MutGl patients. By contrast, isolated DDX41MutSom variants are rarely found in sporadic MDS/AML patients, implying that, like CEBPAMutGl and RUNX1MutGl, DDX41MutGl predispose to a secondary hit on the other allele. Of note, DDX41MutGl patients’ oncogenic events are not enriched with 5q deletion, somatic deletions affecting DDX41 locus, or somatic uniparental disomy. In either circumstance including mouse models, total inactivation of DDX41 appears to be lethal. While DDX41MutGl variants are spread over the protein domains with different hotspots depending on ethnic origin, DDX41MutSom affected mainly two hotpots: p.R525H and p.G530D/C/S located on the helicase domain. The precise timing of clonal evolution and subsequent onset of overt symptoms are not yet elucidated. However, it was shown that ddx41MutSom cells exacerbate ineffective hematopoiesis in ddx41MutGl mouse model and clonal architecture inference on primary patient’s cells suggests that DDX41MutSom is the first main driver event leading to bone marrow blast accumulation.

Regarding prognosis, it seems that IPSS-R/IPSS-M or ELN could not be applied to MDS or AML DDX41MutGl patients. Retrospective studies but also post-hoc analysis of prospective trials comparing DDX41MutGl and DDX41Wt patients reported high response rates to intensive chemotherapy or hypomethylating agents and prolonged survival in these patients. Hematopoietic stem cell transplantation (HSCT) seems to be challenging in DDX41MutGl patients, first for donor selection in the context of a familial predisposition, but also for the induced HSCT toxicity in this frail population.

DDX41MutGl MDS and AML represent a specific and significant entity in myeloid neoplasms, larger studies are needed to establish specific guidelines regarding management and therapeutic options in these patients.

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Background

Germline DDX41 variants have been implicated in autosomal dominant late-onset myeloid neoplasms (MNs). Despite an increasing number of publications regarding this gene, many important features of DDX41-mutated (DDX41^mut) MNs remain to be elucidated, including disease penetrance.

Methods

Here, we enrolled 9,082 cases with various MNs of divergent ethnicity. Tumor-derived DNA was available for all cases at one or more time points. In particular, diagnostic or treatment-naive tumor samples were obtained in 7,697 cases, of which 2,359 had survival data. Germline DNA was available for 1,350 patients. Bone marrow (BM)- or blood-derived tumor DNA was subjected to whole genome, exome and/or targeted sequencing using different driver gene panels, which included DDX41 and an additional 36 genes in common. We also enrolled 20,238 individuals from different Japanese biobanks for population controls.

Results

We identified a total of 346 (3.8%) MNs with pathogenic/likely-pathogenic (P/LP) germline and/or somatic DDX14 mutations among 9,082 MN cases. Among these, 293 (84.7%) had a germline variant, whereas 53 (15.3%) carried somatic variants alone of which biallelic lesions were suspected for 52%. As many as 66.6% of germline variants are truncating, which was rarely true of somatic variants. Based on the genotyping of known leukemia predisposition genes in consecutively enrolled 1,039 Japanese cases with MNs, DDX41 variants explains ~80% of all known predisposition to adult MNs in Japan. We determined the penetrance of MNs for P/LP DDX41 alleles through a kin-cohort analysis involving a total of 288 and 237 first-degree relatives of patients with MNs with and without P/LP DDX41 germline variants, respectively. The risk is almost negligible (~0%) under the age of 40 years, but rapidly increases to 49.3% (95%CI: 29.8-68.2) by the age of 90. In population analysis, five DDX41 alleles showed a significant enrichment in MNs in Japanese populations and therefore represent P/LP alleles (Odds ratio (OR) of ~10; 95%CI: 4.5-22.8, on average), which was more prominent in female than in male (20.7 vs. 5.0 in OR). Accordingly, the penetrance in males (52.5%) almost double that in females (28.7%). DDX41^mut patients with MDS showed a significantly faster progression to AML, which however, confined to those cases having truncating variants, while those with non-truncating variants showed a rather slower progression compared with DDX41^WT patients. Co-mutation patterns at diagnosis and at progression to AML are substantially different between DDX41^mut and DDX41^WT patients. Particularly, CUX1 mutations were overrepresented in DDX41^mut cases. Conspicuously, unlike other MDS cases, DDX41^mut MDS were not significantly enriched for mutations in AML-related genes, such as RAS and other signaling pathway genes. In contrast to DDX41^WT cases, none of the co-mutations significantly affected clinical outcomes. Even biallelic TP53 mutations did not affect overall survival (OS) and as expected, neither IPSS-R nor IPSS-M scores do so. DDX41^mut patients showed a significantly better OS than DDX41^WT cases with higher-risk MDS and sAML patients and a survival comparable to that of DDX41^WT lower-risk MDS cases. OS in patients who received hypomethylating agent (HMA) was significantly better for DDX41^mut than DDX41^WT patients and so in those who received hematopoietic stem cell transplantation (HSCT), which however, confined to those who received HMA prior to HSCT, highlighting a role of HMA treatment in DDX41^mut cases.

Conclusion

P/LP germline DDX41variants explain the largest risk of adult MNs with very high penetrance. DDX41^mut MNs have distinct genetic and clinical/hematological features, representing a unique subset of MNs. IPSS-R/IPSS-M prognostication may not be applied to DDX41^mut MDS.

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Genetic predisposition to MDS is increasingly recognized in a growing subset of MDS patients. Diagnosis of genetic predisposition to MDS informs medical care and treatment decisions. This presentation will discuss recent advances in our understanding of clonal evolution and somatic reversion in Shwachman-Diamond syndrome and Telomere Biology Disorders. Distinct patterns of somatic mutations in patients with germline predisposition to MDS can either alleviate the germline genetic stress resulting in somatic rescue or disrupt cellular checkpoints resulting in increased leukemogenic potential. Tailored considerations guiding recommendations for MDS surveillance will be explored. Evidence for hematologic surveillance strategies that incorporate clinical, pathologic, and molecular data to risk-stratify patients with germline predisposition to MDS will be discussed.

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MDS and AML can develop de novo or secondary to pre-existing hematologic disorders such as in inherited bone marrow failure (including Fanconi anemia [FA]), myeloproliferative neoplasms, MDS or exposure to chemotherapy. Although secondary leukemias represent a highly heterogeneous group, they frequently share features that include BM dysplasia, complex karyotype with del(7q) and frequent TP53 gene inactivation. We studied FA, a DNA damage repair disorder, as a prototypical condition leading to preleukemic clonal hematopoiesis and subsequent sAML in the context of intrinsically stressed hematopoiesis and HSC attrition.

Fanconi anemia (FA) is a genetic condition caused by the inactivation of one of the 22 FANC genes, the products of which interact in the FA pathway involved in DNA repair¹. Most FA patients will develop a progressive bone marrow failure (BMF) during childhood and the diagnosis of FA is usually made at this stage using chromosome break test and FANC genes sequencing². Later in life, during their teens or young adulthood, FA patients have a high risk of developing myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML), in approximately 40% of the patients who did not previously receive HSCT for severe cytopenia.

We performed longitudinal characterization of BM samples in a large cohort of FA patients with clonal evolution using BM morphological staging and high-throughput genomic profiling³. We found a unique somatic pattern of structural variants and mutations that share several features of BRCA-related cancers, the FA hallmark being unbalanced, microhomology-mediated translocations driving copy-number alterations. Patients developed chromosome 1q gain, driving Clonal Hematopoiesis through MDM4 overexpression downmodulating the p53 pathway, later followed by secondary-AML alterations. Functionally, MDM4 trisomy conferred greater fitness to murine and human primary FA HSPCs, rescued inflammation-mediated bone marrow failure and drove clonal dominance in FA mouse models. Conversely, targeting MDM4 impaired leukemia cells in vitro and in vivo. By contrast, mutations of other MDS/AML oncogenes and tumor suppressor genes were rarely found.

Our results identify a linear route towards secondary leukemogenesis whereby early MDM4-driven downregulation of basal p53 activation plays a pivotal role. Importantly, our comprehensive analysis suggests that timely staging and treatment, including using potential targeted therapy, should improve the care of FA patients. Beyond FA, this oncogenic sequence as highlighted in our work, i.e. clonal hematopoiesis that attenuates the p53 response, followed by additional oncogenic events leading to MDS/AML, can also be found in other “stressed hematopoiesis” conditions such as post-BMF, MDS, MPN and post-therapy leukemia, as a general canonic route leading to secondary leukemia^3,4,5.

1. Ceccaldi, R., Sarangi, P., and D’Andrea, A.D. The Fanconi anaemia pathway: new players and new functions. Nat. Rev. Mol. Cell Biol 2016. 17, 337–349.

2. Shimamura, A., and Alter, B.P. Pathophysiology and management of inherited bone marrow failure syndromes. Blood Rev 2010. 24, 101–122.

3. Sebert M, Gachet S, Leblanc T, Rousseau A, Bluteau O, Kim R, Ben Abdelali R, Sicre de Fontbrune F, Maillard L, Fedronie C, Murigneux V, Bellenger L, […], de Thé H, Antoniewski C, Bluteau D, Régis Peffault de Latour R, Soulier J. Clonal hematopoiesis driven by chromosome 1q/MDM4 trisomy defines a canonical route towards leukemia in Fanconi anemia. Cell Stem Cell 2023, Feb 2;30(2):153-170.e9

4. Kennedy, A.L., Myers, K.C., Bowman, J., Gibson, C.J., Camarda, N.D., Furutani, E., Muscato, G.M., Klein, R.H., Ballotti, K., Liu, S., et al. (2021). Distinct genetic pathways define pre-malignant versus compensatory clonal hematopoiesis in Shwachman-Diamond syndrome. Nat. Commun. 12, 1334.

5. Wong, T.N., Miller, C.A., Jotte, M.R.M., Bagegni, N., Baty, J.D., Schmidt, A.P., Cashen, A.F., Duncavage, E.J., Helton, N.M., Fiala, M., et al. (2018). Cellular stressors contribute to the expansion of hematopoietic clones of varying leukemic potential. Nat. Commun. 9, 455.

Background And Aims

Deleterious germline CHEK2 variants (CHEK2MutGL) have been associated with an increased risk of solid cancers and more recently with myeloid malignancies (MM). However, the prevalence and characteristics of CHEK2MutGL patients with MM remain to be determined.

Methods

Our analysis was initially focused on 2322 adult patients with a MM diagnosed at St-Louis hospital Paris (cohort #1) for whom capture-based NGS was performed on bone marrow or peripheral blood, and was then completed by 322 MDS patients enrolled in MDS trials AZA-plus and AZA-EPO (independent cohort #2).

Results

In cohort #1, we identified 14 pathogenic/likely pathogenic germline CHEK2 variants within 19 patients, representing a frequency of 0.8% (19/2322). Patients had mostly MDS with a median age of 72 years at diagnosis (Table 1), with normal karyotype (39%), and frequent additional driver mutations (95%). Of note, two out of them carry a second somatic hit in CHEK2 (Figure 1). Hematological and survival outcomes of the 19 patients were heterogeneous (Figure 2).

In the specific MDS cohort (#2), the frequency of CHEK2MutGL patients was 1.5 % (5/322) consistent with the high frequency of MDS in our first CHEK2MutGL cohort#1 concerning nevertheless few patients.

Conclusions

In our study, CHEK2MutGL patients represent 0.8% and 1.5% of MM and MDS, respectively. These patients do not seem to have specific hematological features and may be less frequent than previously suggested. The absence of a specific entity in CHEK2MutGL MDS patients is in line with what is reported in solid cancer.

Background And Aims

Germline DDX41 variants are implicated in late-onset myeloid neoplasms, accounting for the largest germline risk of the development of myeloid neoplasms. In typical cases, a germline loss-of-function allele is compounded by the somatic R525H mutation affecting the helicase domain in the remaining allele. The molecular mechanism by which DDX41 mutations lead to myeloid neoplasms remains to be elucidated.

Methods

To delineate the pathogenic mechanism of DDX41-mutated myeloid neoplasms, we generated mice models carrying the conditional Ddx41 knock-out and/or R525H knock-in alleles.

Results

In non-competitive bone marrow (BM) transplantation, most of the mice reconstituted with Ddx41^-/- or Ddx41^R525H/- BM died within a month due to severe BM failure. By contrast, the mice transplanted with Ddx41^+/- or Ddx41^R525H/+ BM showed significantly reduced WBC counts in long-term observation. Some of the Ddx41^+/- or Ddx41^R525H/+ BM-transplanted mice developed hypocellular BM with evidence of erythroid dysplasia without developing overt AML.

In competitive transplantation, Ddx41^-/- or Ddx41^R525H/- mice-derived cells showed markedly disadvantageous reconstitution, while Ddx41^+/- or Ddx41^R525H/+ mice-derived cells showed slightly reduced reconstitution compared to Ddx41^+/+ mice-derived cells.

Transcriptome analysis of Ddx41^R525H/--derived stem cells exhibited a significant upregulation of genes involved in innate immunity, including cGAS-STING pathways, whereas there was a downregulation of genes related to RNA metabolism and ribosome biogenesis.

Conclusions

Our results revealed that monoallelic Ddx41 loss-of function led to age-dependent impaired hematopoiesis, while compound biallelic loss-of function and R525 alleles showed a compromised function of hematopoietic stem cells, where activated innate immunity and impaired ribosome functions may play important roles.