Abstract: Introduction Recent studies indicate that particularly in a subgroup of younger patients, acute myeloid leukemia (AML) develops due to an inherited genetic predisposition linked to mutations in genes such as ANKRD26, SAMD9, SAMD9-L, GATA-2, genes causing telomere biology disorders or Shwachman-Diamond syndrome. However, the prevalence of so-called "AML predisposition syndromes" (APS) underlying newly diagnosed cases with AML is unknown. Actual screening strategies for APS are based on the family history and clinical/genetic features. There is growing evidence that APS frequently manifest themselves with an oligosymptomatic phenotype or are lacking specific symptoms altogether. Furthermore, molecular analysis of the clonal population without additional analysis of non-clonal cells do not allow the discrimination between inherited and acquired changes. Thus, new approaches to identify the subset of patients with underlying APS in adult newly diagnosed AML patients are needed. One frequent feature observed in APS is younger age at the time of diagnosis and the initial presence of an aberrant karyotype. Along this line, we retrospectively screened the German SAL-AML registry using age and the presence of an aberrant karyotype as pre-defining parameters to analyze the prevalence of APS in this selected cohort. Patients and methods The database of the German SAL-AML registry includes over 5207 patients with AML. We screened for patients below 35 years of age and with any type of numerical or structural chromosomal aberration at first diagnosis. DNA samples of patients achieving cytological remission (CR) and available samples of peripheral blood or bone marrow were selected. CR samples were chosen to reduce potential contamination by malignant AML blasts. Patients were screened for pathogenic variants using a self-designed NGS panel containing the entire coding sequences of ACD, ANKRD26, CTC1, DDX41, DKC1, ERCC6, ETV6, GATA1, GATA2, LIG4, NHP2, NOP10, PARN, POT1, RPA1, RPL11, RPL15, RPL26, RPL35A, RPL5, RPS10, RPS17, RPS19, RPS24, RPS26, RPS7, RTEL1, SAMD9, SAMD9L, SBDS, SRP72, TERC, TERF1, TERF2, TERT, TINF2, TPP1 and WRAP53. An inherited variant was considered in all patients with a variant allele frequency between 40-60% for heterozygous variants and & gt;90% for homozygous ones. To analyze the functional consequence of SAMD9 variants, proliferation assays with HEK293 cells transfected with the respective identified variant was carried out. Results and discussion On the basis of the inclusion criteria mentioned above, we were able to identify 41 patients. All cases except one were considered de novo AML by the treating physicians and received an anthracycline/cytarabine based induction chemotherapy. Mean age of the 41 patients was 26 ± 5 years (mean ± S.D.). Predominant karyotypic aberration were abnormalities of chromosome 8 (18/41) as well as a complex aberrant karyotype (29/41). NGS analysis revealed five different heterozygous mutations in approx. 10% (4/41) of patients: GATA2 c.1009C & gt;T p.(Arg337Ter), SBDS c.183_184delInsCT and c.258+2T & gt;C (both mutations in the same patient), TINF2 c.848C & gt;A p.(Pro283His), SAMD9 c.2854G & gt;C p.(Gly952Arg). The variants in GATA2, SBDS and TINF2 are known to be pathogenic. For SAMD9, in vitro experiments showed increased inhibition of cell growth compared to wild-type supporting the pathogenicity of the mutation. Focusing on the clinical outcome, 50% (2/4) of the identified APS patients received allogeneic transplantation during follow-up compared to 65% (24/37) in the group without detectable mutations. Median survival in the APS group was significantly shorter with 3.2 months compared to 105.3 months in the remaining 37 AML patients (p & lt;0.001). Conclusions Using age and karyotype as selection criteria, we were able to identify an inherited APS in 10% of newly diagnosed AML patients below 35 years with chromosomal aberrations reaching CR. Obviously, our study is limited by rather stringent inclusion criteria not allowing overall conclusions on the incidence of APS in newly diagnosed AML. However, age and karyotype might provide simple clinical parameters to trigger genetic screening for inherited APS in addition to the actual recommendations. Given the significant difference in survival in patients with and without underlying APS, our study clearly supports inclusion of screening for APS in this cohort pending prospective validation. Figure Disclosures Röllig: Amgen, Astellas, BMS, Daiichi Sankyo, Janssen, Roche: Consultancy; Abbvie, Novartis, Pfizer: Consultancy, Research Funding. Müller-Tidow:Daiichi Sankyo: Research Funding; Pfizer: Research Funding, Speakers Bureau; Janssen-Cilag GmbH: Speakers Bureau; BiolineRx: Research Funding. Panse:Blueprint Medicines: Consultancy, Membership on an entity's Board of Directors or advisory committees; Alexion: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Boehringer Ingelheim: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Chugai: Speakers Bureau; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; F. Hoffmann-La Roche Ltd: Consultancy, Membership on an entity's Board of Directors or advisory committees; MSD: Consultancy, Membership on an entity's Board of Directors or advisory committees; Grunenthal: Consultancy, Membership on an entity's Board of Directors or advisory committees; BMS: Consultancy, Membership on an entity's Board of Directors or advisory committees; Apellis: Consultancy, Membership on an entity's Board of Directors or advisory committees. Brümmendorf:Pfizer: Consultancy, Honoraria, Other: Travel, Accommodation, Expenses, Research Funding; Novartis: Consultancy, Other: travel, accommodation, expenses, Research Funding; Janssen: Consultancy; Merck: Consultancy; Takeda: Consultancy. Jost:Roche: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Astellas: Membership on an entity's Board of Directors or advisory committees; Celgene: Other: travel support; JAZZ: Other: travel support.

Abstract: Introduction: Acquired aplastic anemia (AA) is typically characterized by pancytopenia and bone marrow (BM) failure mostly due to an autoimmune attack against the hematopoietic stem cell compartment. Thus, AA patients frequently respond to immunosuppressive therapy (IST). Hypoplastic myelodysplastic syndrome (hMDS) frequently mimics clinical and morphological features of AA and proper clinical discrimination of hMDS from AA sometimes remains difficult. Interestingly, some cases of hMDS respond at least partially to IST and on the other hand, AA can clonally evolve to hMDS. Telomeres shorten with each cell division and telomere length (TL) reflects the replicative potential of somatic cells. Whereas it is proposed that TL can to some degree discriminate hereditary subtypes of bone marrow failure syndromes from classical acquired forms, the role of TL for disease pathogenesis in hMDS remains unclear. In this study, we therefore aimed to investigate accelerated TL shortening as a possible (bio-)marker to distinguish hMDS from AA. Patients and Methods: TL of BM biopsies at diagnosis of 12 patients with hMDS and 15 patients with AA treated in the University Hospital Düsseldorf were analyzed. Mean age was 45.2 years in AA patients and 65.2 years in patients with hMDS. Confocal Q-FISH protocol was used for TL measurement as published previously (Blood, 2012). TL analysis was performed in single-blinded fashion. 28 patients (range 18-80 years) with newly diagnosed M. Hodgkin without BM affection were used as controls for linear regression and calculation of age-adapted TL difference. For the analysis of the data, we made use of a recently developed mathematical model of TL distribution on the stem cell level allowing us to extrapolate mean TL shortening per year (TS/y) based on the individual TL distributions of captured BM biopsies. Results: Using the controls to adjust for age, we found that age-adapted TL was significantly shortened both in patients with AA (median: -2.96 kb, range -4.21 to 0.26, p=0.001) and patients with hMDS (median: -2.26, range -3.85 to -0.64, p=0.005). In direct comparison, telomere shortening was more accelerated in patients with AA as compared to hMDS (p=0.048). Next, we analyzed the TL shortening per year (TS/y) based on the individual telomere distribution. Calculating the extrapolated TL shortening per year (TS/y), we found significant increased TS/y in AA patients (mean±SD: 235,8 bp/y±202,9, p=0.001) and hMDS patients (120,5±41,7 bp/y, p=0.0001) compared to controls (37,5±18,9 bp/y). Interestingly, the extrapolated rate of TS/y remained stable at different ages in hMDS patients as observed in healthy controls. In contrast, TS/y in AA patients showed a strong age-dependence with a maximum of TS/y in patients younger than 30 years (R²=0.42, p=0.008). Finally, we set to test whether TS/y can be used to identify AA or hMDS patients. Using 150 bp TS/y as a cut-off (4-fold the mean of controls), we found significantly more AA patients (10/15, 66.7%) had accelerated TL shortening compared to hMDS (1/12, 8.3% p=0.005). Conclusion: We provide first retrospective data on TL in patients with hMDS using confocal Q-FISH. Age-adapted TL is significantly shorter in patients with AA compared to hMDS. Interestingly, telomere shortening per year is both significantly increased in AA as compared to hMDS patients as well as in both groups compared to controls. The rate of telomere shortening TS/y might represent a new marker in patients with bone marrow failure syndromes that allows to discriminate AA from hMDS patients pending prospective validation. Disclosures No relevant conflicts of interest to declare.

Abstract: Introduction: Telomere biology disorders (TBD) are caused by mutations affecting proper telomere maintenance resulting in premature telomere shortening. Telomere length (TL) assessment is currently being used for screening and diagnosis of TBD of which Dyskeratosis congenita (DKC) is the most prominent TBD subtype typically found in children and adolescents. In adults, TBDs are characterized by a broad spectrum of more "cryptic" diverging mono- or oligosymptomatic clinical manifestations such as bone marrow failure (BMF), hepatopathy or interstitial lung disease (ILD). However, despite growing general clinical awareness and exertion of improved TL screening strategies, insufficient data are available about the clinical course of adult, late-onset TBDs. Here, we present a series of 41 consecutive adult TBD cases from 2014 to 2021 identified through the Aachen Telomeropathy registry. Methods and Patients: Median follow-up of the cohort was 2.0 (range 0-6.2) years. In 39/41 patients TBD diagnosis was established based on coexistence of the following three criteria: 1.) Identification of pathogenic variant in a known TBD-related gene via next-generation panel sequencing (NGS) or sequential whole exome sequencing (WES). 2.) The presence of prematurely shortened TL below the 1% percentile (39/41) or 5% percentile (2/41) in the lymphocyte gate detected by flow-FISH and 3.) the presence of BMF or ILD as predominant clinical manifestation. In 2 out of 41 cases, WES did not identify a definitive pathogenic variant. Here, diagnosis of TBD was established due to short telomere below the 1% percentile, BMF and the presence of typical DKC stigmata, other TBD symptoms and a positive family history. Results: Mean age of our cohort was 35.9 ± 17.6 years. 49% (n=20) of patients were females. Results of the genetic screening revealed heterozygous pathogenic variants in TERC (n=14) and TERT (n=11) as the most frequent variants, followed by RTEL1 (n=6), TIN2 (n=1), CTC1 (n=1) and DKC1 (n=1). Homozygous or compound heterozygous pathogenic variants were found for CTC1 (n=2), NHP2 (n=2) or TCAB1 (n=1). 46% (n=19) of patients had a positive family history. BMF was the most frequent symptom with 93% (n=38) presenting with leukopenia, 78% (n=32) with anemia and 76% (n=31) with thrombocytopenia. ILD was suspected/confirmed clinically in 44% (n=18), hepatopathies in 29% (n=12) and cancer in 12% of the patients in past medical history (n=5, liposarcoma, breast cancer, Hodgkin lymphoma, diffuse large B-cell lymphoma, endometrial cancer). Symptoms of the typical DKC triad (leukoplakia, nail dystrophy, abnormal skin pigmentation) were observed in 41% (n=17). Of those, 76% (13/17) presented with only one or two clinical signs. Based on past medical history, the onset of first TBD manifestation was observed at a mean age of 26.9 ± 18.3 years. Time from first symptom observed to the diagnosis of TBD was 8.2 ± 9.5 years. 22% (n=9) patients died during follow-up with mean time of 11.7 ± 10.1 years from first manifestation of TBD to death. Regarding treatment, 39% (n=16) were listed for allogeneic stem cell transplantation (allo Tx), but only 38% (6/16) of these eventually received allo Tx. Immunosuppressive therapy with ATG and CSA was carried out in 12% (n=5) of the patients with no patient responding to treatment. Eltrombopag was given in 5% of cases (n=2) without response. 15% (n=6) received androgen treatment with danazol as the most frequently used drug in five of the six reported cases. All patients showed a response at least in one hematological lineage. Conclusions: Our data support the notion that despite the recent progress in screening and genetic diagnostics, late-onset TBD is still frequently underdiagnosed with several years from first manifestation of disease to diagnosis. Implementation of routine screening for TBD might improve the rate of correct TBD diagnosis and could help to avoid ineffective treatments. Disclosures Beier: Pfizer: Membership on an entity's Board of Directors or advisory committees; Jazz: Other: Travel reembursement; Alexion: Speakers Bureau. Roeth: Novartis: Consultancy, Honoraria; Sanofi: Consultancy, Honoraria; Kira: Consultancy, Honoraria; Bioverativ, a Sanofi company: Consultancy, Honoraria; Roche: Consultancy, Honoraria, Research Funding; Apellis Pharmaceuticals: Consultancy, Honoraria; Alexion Pharmaceuticals Inc.: Consultancy, Honoraria. Platzbecker: AbbVie: Honoraria; Novartis: Honoraria; Celgene/BMS: Honoraria; Janssen: Honoraria; Takeda: Honoraria; Geron: Honoraria. Radsak: Novartis: Consultancy, Honoraria, Other: e.g. travel support; JAZZ: Other: e.g. travel support; Takeda: Consultancy, Honoraria; Celgene/BMS: Consultancy, Honoraria, Other: e.g. travel support; Daiichi Sankyo: Consultancy, Honoraria, Other: e.g. travel support; Astellas: Other: e.g. travel support; Incyte: Consultancy, Honoraria; Corat: Consultancy, Honoraria; Cogent Biosciences: Consultancy, Honoraria; TEVA: Consultancy, Honoraria; Otsuka: Consultancy, Honoraria; Amgen: Other: e.g. travel support; Abbvie: Other: e.g. travel support. Schafhausen: Blueprint Medicines: Membership on an entity's Board of Directors or advisory committees; Alexion: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; MSD: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Swedish Orphan Biovitrum AB: Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees. Corbacioglu: Gentium/Jazz Pharmaceuticals: Consultancy, Honoraria. Heuser: AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Honoraria; BergenBio: Research Funding; BMS/Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Daiichi Sankyo: Membership on an entity's Board of Directors or advisory committees, Research Funding; Jazz: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Bayer Pharma AG: Research Funding; Astellas: Research Funding; Karyopharm: Research Funding; Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding; Roche: Membership on an entity's Board of Directors or advisory committees, Research Funding; Tolremo: Membership on an entity's Board of Directors or advisory committees. Koschmieder: Incyte: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: (e.g. travel support); Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: (e.g. travel support); Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: (e.g. travel support); Karthos: Other: Travel support; Shire: Honoraria, Other; CTI: Membership on an entity's Board of Directors or advisory committees, Other; Sanofi: Membership on an entity's Board of Directors or advisory committees, Other: Travel support; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel support, Research Funding; Geron: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: (e.g. travel support), Research Funding; Alexion: Other: Travel support; BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: (e.g. travel support); Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: (e.g. travel support), Research Funding; Ariad: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: (e.g. travel support); Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees; Baxalta: Membership on an entity's Board of Directors or advisory committees, Other; Abbvie: Other: Travel support; Image Biosciences: Other: Travel support; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel support, Research Funding; AOP Pharma: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: (e.g. travel support), Research Funding. Panse: Blueprint Medicines: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Chugai: Speakers Bureau; Pfizer: Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Boehringer Ingelheim: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Alexion: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; F. Hoffmann-La Roche Ltd: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; MSD: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Grunenthal: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol Myers Squibb: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Apellis Pharmaceuticals: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Isfort: Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel reimbursement; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel reimbursement; Ariad: Honoraria, Membership on an entity's Board of Directors or advisory committees; Incyte: Honoraria, Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria; Hexal: Other: Travel reimbursement; Mundipharma: Other: Travel reimbursement; Amgen: Other: Travel reimbursement; Roche: Other: Travel reimbursement; Alexion: Other: Travel reimbursement. Brummendorf: Bristol Myers: Research Funding; Janssen: Honoraria; Novartis: Honoraria, Patents & Royalties, Research Funding; Pfizer: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Repeat Diagnostics: Research Funding; Takepart Media: Honoraria.

Abstract: Introduction: Classical Dyskeratosis Congenita (DKC) is a systemic disorder characterized mainly by mucocutaneous features and bone marrow failure. DKC is caused by mutations affecting proper telomere maintenance leading to premature telomere shortening. Clinically, assessment of telomere length (TL) is being used for screening and diagnosis of DKC. Previous studies showed that androgen derivatives (AD) such as danazol or oxymetholone can improve blood counts and reduce transfusion frequency in patients with DKC. Reports from in vitro studies suggest that AD can increase the expression of telomerase and elongate telomeres reversing at least partially the mutation-related haploinsufficiency of the telomerase complex. However, whether telomere elongation can be observed in vivo is still controversial. Patients with DKC have an increased risk of developing solid tumors and acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS). Malignant transformation occurs mostly by chromosomal instability mediated by critical short telomeres and not via clonal hematopoiesis (CHIP) and eventual selection for MDS-related somatic mutations. The question whether increased telomerase activity by AD increases the risk for additional MDS-related mutations is unclear. In our study, we aimed to investigate TL and MDS-related somatic mutations in DKC patients undergoing treatment with AD. Methods and Patients: 5 patients enrolled in the Aachen Telomeropathy Registry (ATR) that underwent AD treatment were included in the analysis. All patients had molecularly confirmed DKC (4 patients having mutations in TERC, 1 patient in TERT). TERC mutated patients received danazol treatment (mean dosage 625 mg per day) while the patient with TERT mutation was treated with low dose oxymetholone (0.22mg/kg) per day. Patients were at a median age of 43.1 (range from 21.7 to 53.8) years. Median duration of treatment with AD was 14 months (3 to 29 mo) and is actually ongoing in all patients treated with danazol. Follow-up for blood counts and TL length assessment was carried out after median 14 months after treatment start with AD. TL assessment and blood counts of the patient receiving oxymetholone was carried out at the end of AD treatment after 29 months. All patients underwent next-generation sequencing (NGS) analysis using custom NGS-panel including frequent genes implicated in MDS development. Quality parameters of the NGS analysis were satisfactory (Q30 〉 85%) and 95% of the expected area was covered at minimum 300x. To minimize risk of detecting sequencing errors, a threshold of 10 (absolute) and 5% (relative) variant allele frequency (VAF) was chosen. TL assessment of peripheral blood granulocytes and lymphocytes was carried out by Flow-FISH and all results are given in kb. Results: Analysis of the peripheral blood counts revealed a significant increase in platelets counts from mean 56/nl ±50 S.D. before treatment to 88/nl ±49 (p=0.03) during treatment. Similar results were observed for leukocyte counts increasing significantly from 3.83/µl±1.86 to 4.70/µl±2.88 (p=0.04). Hemoglobin counts showed a non-significant increase from 8.9 g/dl ±2.6 to 10.2 g/dl ±2.9 (p=0.13, all student paired t-test). Focusing on TL, lymphocyte TL increased significantly from 4.32kb±0.47 to 5.13kb ±0.57 (p=0.001). TL in the granulocyte subpopulation increased from 4.73kb±0.33 before treatment start to 6.10kb±0.50 under treatment (p=0.026). Calculated median increase in TL per months for lymphocytes and granulocytes was 0.092 kb (0.019 to 0.223 kb) and 0.166 kb (0.019kb to 0.513kb). Finally, NGS analysis for possible MDS-related mutations did not reveal any mutations before and under AD treatment. Conclusions: Based on our data in this genetically homogenous cohort of 5 patients with mutations in the telomerease genes TERC and TERT and short TL, AD significantly improve blood counts and elongate telomeres in granulocytes and lymphocytes. No MDS-related somatic mutations were observed during telomerase activation with AD. Pending longer follow up, treatment with AD seems to represent an efficient and safe therapy for patients with TERT or TERC mutations. Whether AD persistently elongate telomeres in DKC patients and how much this is dependent on the underlying DKC-related mutation requires further investigation. Disclosures Kirschner: Basilea Pharmaceutica: Other: travel support; BMS: Consultancy; Bayer: Consultancy; Roche: Consultancy. Wilop:Medizinwelten-Services GmbH: Honoraria; Amgen: Consultancy; Celgene: Consultancy, Honoraria, Other: Travel grant; Bristol-Myers Squibb: Honoraria. Brümmendorf:Pfizer: Consultancy, Research Funding; Janssen: Consultancy; Novartis: Consultancy, Research Funding; Takeda: Consultancy; Merck: Consultancy. Beier:Gilead: Other: travel support; Celgene: Other: travel support.

Abstract: Dyskeratosis Congenita (DKC) is a systemic disorder caused by mutations resulting in impaired telomere maintenance. Clinical features include bone marrow failure and an increased risk of developing hematological malignancies. There are conflicting data whether androgen derivatives (AD) can elongate telomeres in vivo and whether AD treatment enhances the risk of gaining myelodysplastic syndrome‐related mutations. Seven TERC or TERT ‐mutated DKC patients underwent AD treatment. All patients revealed hematological response. Telomere length of lymphocytes and granulocytes increased significantly and no MDS‐related mutations were detected. Pending longer follow‐up, treatment with AD seems to represent an efficient and safe therapy for DKC patients.