Telomere attrition is common in patients with germline RUNX1 pathogenic variants Free

Introduction Familial platelet disorder with associated myeloid malignancy (FPDMM) is a rare, autosomal dominant hematologic malignancy predisposition syndrome caused by germline RUNX1 pathogenic variants. Patients exhibit a high lifetime incidence (35-45%) of developing hematologic malignancies, making early genetic diagnosis essential. As RUNX1 encodes a transcription factor, previous research has focused mainly on transcriptomic changes. Telomeres are important for maintaining genomic stability by preventing the loss of genetic information during cell division. Shortened telomeres have been identified in several inherited blood diseases other than telomere biology disorders (TBD), all of which are associated with increased risk of leukemia development. Yet, telomere length (TL) has not been investigated in patients with germline pathogenic RUNX1 variants. ObjectiveWe hypothesized that telomere erosion is a feature of FPDMM patients in addition to thrombocytopenia, marrow dysplasia, and increased malignancy risk. In this study, we characterized the TL in FPDMM patients from the largest, single-center natural history study of FPDMM (NCT03854318). MethodsWe prospectively assessed 40 FPDMM patients between May 2024 and March 2025, encompassing 23 families with 19 unique RUNX1 variants, all pathogenic (P) or likely pathogenic (LP). Samples were also analyzed from six additional patients with variants of uncertain significance (VUS), but were not included in the main analysis. Using clinical automated multicolor flow cytometry-fluorescence in situ hybridization (flow-FISH), we determined lymphocyte and granulocyte TLs in peripheral blood samples. No patients with active or prior hematologic malignancy were included. ResultsThe median age in the study was 30 years (range 2-66). We observed shortened TL in both lymphocytes and granulocytes, which was significantly below age-adjusted 50th percentile in all patients (lymphocytes, p=1.8x10^-30); granulocytes, p=6.5x10^-42). In 87.5% of FPDMM patients, lymphocyte TL was shortened (<10th percentile), and this was even more common in granulocytes at 95%. Granulocytes showed significantly greater TL shortening than lymphocytes (-2.4 vs -1.7 kb, p=8.59x10^-7). Longitudinal data from two siblings with a shared RUNX1 frameshift mutation (Arg346Profs*249) over nine years revealed ongoing TL shortening in both, with granulocytes crossing from the 10th to below the 1st percentile. Next-generation sequencing found no mutations, and RNA sequencing of CD34+ cells showed no changes in genes related to telomere biology. Somatic mutations were identified in 32.5% of patients in our FPDMM cohort; however, clonal hematopoiesis did not affect TL severity. Lastly, surprisingly, the measured FPDMM lymphocyte TL mean deviation from age-adjusted median (ΔT) was significantly greater than that of severe aplastic anemia (SAA) (-1.7 vs -0.5 kb, p<0.0001), but significantly less than TBD; -2.9 kb (p<0.0001). The same pattern of significant differences was observed in granulocyte TLs. These data highlight the severity of telomere erosion seen in FPDMM, which was comparable to that seen in SAA and other TBD. ConclusionsPremature TL shortening is a common genomic alteration in patients with germline RUNX1 variants and FPDMM. This finding opens new avenues for hypothesis testing and future mechanistic studies. The mechanism for TL shortening is unclear, and whether RUNX1 has a direct or indirect role in telomere regulation remains to be determined. The observation that granulocyte TLs were significantly shorter than those in lymphocytes (T and B cells) could be because granulocytes require constant replenishment from hematopoietic stem cells, whereas lymphocytes are long-lived and can activate telomerase during cell division to counteract TL shortening. Interestingly, this leukocyte subtype discordance is also observed in SAA, and FPDMM TLs are significantly shorter than SAA patients. Furthermore, data from two siblings over nine years suggest that germline RUNX1 variants may be associated with accelerated telomere attrition. However, the longitudinal sample size is limited, making it difficult to draw definitive conclusions. Our data show that germline mutations in a transcription factor gene may lead to telomere shortening. Therefore, FPDMM should be considered in differential diagnosis when patients present with thrombocytopenia, short telomeres, and increased risk of malignancy.