Clinical and translational studies of RUNX1 and FPD

RUNX1的种系突变导致家族性血小板疾病伴髓系恶性肿瘤（FPDMM），这是一种罕见的常染色体显性遗传病。患有这种疾病的患者有巨核细胞发育缺陷，血小板计数低，血小板功能缺陷导致凝血缺陷，并易患血液系统恶性肿瘤。FPDMM患者具有终身造血恶性肿瘤的风险，具有不同RUNX1种系突变的家族之间的临床表现和疾病外显率不同，甚至在具有相同RUNX1突变的单个家族中的受影响个体之间也是如此。目前还没有好的生物标志物或简单的检测方法来预测疾病的结果，患者需要每年去办公室就诊，并进行侵入性手术，如骨髓活检，以监测他们的疾病进展。许多FPD患者没有发生白血病的事实表明，RUNX1突变本身并不足以导致白血病的发生；在克隆进化之后还需要额外的体细胞突变。几项研究表明，正常RUNX1等位基因的体细胞突变可能是第二个打击之一。此外，ASXL1、CBL、CDC25C、FLT3、PHF6、SRSF2和WT1已被鉴定为反复突变基因。然而，这些研究大多是基于相对较小的患者队列，研究结果并不总是相互一致。最重要的是，目前还不清楚这些突变基因是否在白血病的发展中起作用。

Germline mutations in RUNX1 cause familial platelet disorder with associated myeloid malignancies (FPDMM), a rare autosomal dominant disease. Patients with this disorder have defective megakaryocytic development, low platelet counts, defective platelet functions that lead to clotting defects, and predisposition of the patients for hematological malignancies. FPDMM patients have a life-long risk of hematopoietic malignancies, with variable clinical presentation and disease penetrance among families with different RUNX1 germline mutations, and even between affected individuals within a single family who have the same RUNX1 mutation. Currently there are no good biomarkers or easy assays to predict disease outcome, and the patients need to have annual office visits and invasive procedures such as bone marrow biopsy to monitor their disease progress. The fact that many FPD patients do not develop leukemia suggest that RUNX1 mutation by itself is not sufficient for leukemogenesis; additional somatic mutations followed by clonal evolution are needed. Several studies suggest that somatic mutations in the normal RUNX1 allele could be one of the second hits. In addition, ASXL1, CBL, CDC25C, FLT3, PHF6, SRSF2 and WT1 have been identified as recurrently mutated genes. However, most of these studies were based on relatively small patient cohorts and the findings do not always agree with each other. Most importantly, it is not clear if any of these mutated genes play roles in leukemia development. To address these issues for better understanding of the clinical course and underlying pathogenic mechanism of FPDMM, we launched a natural history study of FPDMM at the NIH Clinical Center in early 2019. https://clinicaltrials.gov/ct2/show/NCT03854318 https://clinicalstudies.info.nih.gov/ProtocolDetails.aspx?A_19-HG-0059.html%20InternalRUNX1 The goals of the natural history study are to identify and follow patients with FPDMM with the hope of identifying biomarkers that can predict which patients will progress and develop malignancies and to identify secondary gene mutations that may impact clinical presentation, disease severity, and progression to malignancies. Through our study we hope to determine genotype-phenotype correlations for RUNX1 mutations and validate the importance of 2nd hits that cooperate with RUNX1 germline mutations for leukemogenesis. And we desire to comprehensively phenotype the patients to determine the full spectrum of the manifestations of the germline RUNX1 mutations. We started to enroll patients in July 2019 and so far, we have enrolled 49 FPDMM patients and 44 family controls from 25 families. Enrolled patients have been invited to visit NIH CC yearly for comprehensive checkups. They typically spend 1-3 days at the NIH, with extensive phenotyping at the Clinical Center, including bone marrow aspiration/biopsy as well as other clinical & research labs, procedures, imaging, and subspecialty consultations when needed. We collect peripheral blood and bone marrow samples for hematological tests as well as genomic sequencing tests. We focus our attentions on documenting clinical manifestations associated with FPDMM, including those outside of the hematopoietic system. As expected, almost all patients have reduced platelets and/or morphological/functional defects of platelet. Some patients have abnormalities affecting other blood lineages as well. Many patients have eczema and/or allergies, and others have GI problems. We are still accumulating and analyzing data to determine if any of these non-hematopoietic findings are related to RUNX1 mutations. Targeted panel sequencing, whole exome sequencing, RNA-seq, and SNP-array have been performed with bone marrow and peripheral blood samples from the patients to detect secondary mutations and clonal hematopoiesis, as well as to characterize disease progression. We plan to prospectively sequence blood and bone marrow samples obtained yearly from these FPDMM patients and correlate the findings with clinical observations. We will also use model systems, both cell culture models and animal models, to perform functional and translational studies based on our findings in the patients. We are encouraged by our successful enrollment efforts during this first full year of our clinical study, and we anticipate a fairly large cohort of FPDMM patients in the near future.