Date of Award

January 2024

Document Type

Open Access Thesis

Degree Name

Medical Doctor (MD)

Department

Medicine

First Advisor

Alexa J. Siddon

Abstract

Paroxysmal nocturnal hemoglobinuria (PNH) is a clonal blood disorder frequently associated with bone marrow failure that in rare instances can progress to leukemia. PNH clones of varying sizes occasionally present even in patients with hematologic malignancies and no known history of classical PNH, particularly in myelodysplastic neoplasms (MDS). Curiously, somatic driver mutations considered to be pathogenic and likely pathogenic in myeloid leukemias can be found in phenotypically normal, elderly individuals, as well as those with clonal disorders such as PNH, clonal hematopoiesis of indeterminate potential (CHIP), and age-related clonal hematopoiesis (ARCH). These mutations may be the critical link between PNH and the development of cancer. We suspect that PNH clones, derived from mutations in PIGA, may reflect a disordered bone marrow prone to additional genetic hits involved in tumorigenesis. It is uncertain, however, whether leukemic cells directly arise from PNH+ progenitors with additional genetic variants or if they are in fact distinct populations. Moreover, the specific driver mutations that underlie both PNH and myeloid neoplasms remains an area of active investigation. Our study aims to characterize the prevalence of myeloid neoplasm-associated somatic mutations in older adults and in patients who develop myeloid malignancies (MN+ patients), stratified by whether they also harbor PNH clones. We retrospectively examined the initial genetic evaluation by next-generation sequencing (NGS) of 197 individuals at Yale-New Haven Hospital and elicited the most common driver mutations and their association with age and PNH clonal presence. We demonstrated that pathogenic and likely pathogenic somatic mutations increased with age (average age of patients with one or more mutations was 69.8 years compared to 58.0 years in those with no mutations of interest, p< 0.0001). Variants in SF3B1 (average age= 74.4 years, p= 0.0015), TP53 (average age= 72.8 years, p= 0.0057), SRSF2 (average age= 72.4 years, p= 0.0024), DNMT3A (average age= 71.9 years, p= 0.0059), TET2 (average age= 70.8 years, p= 0.0032), ASXL1 (average age= 70 years, p= 0.0052), and U2AF1 (average age= 69.7 years, p= 0.0082) were most commonly present in adults who were significantly older than those with no relevant mutations.

Those with a diagnosis of a myeloid neoplasm were drastically more likely to harbor driver mutations (81.1% with at least one variant of interest vs. 23.5% among those without a myeloid neoplasm, p< 0.0001), and had a greater number of mutations on average (1.95 vs. 0.38 mutations per patient, p< 0.0001). Interestingly, MN+ patients who had a PNH clone ≥0.01% were significantly more likely to possess a neoplasm-associated mutation than those with no PNH clones (91.9% vs. 60.6%, p= 0.0005), indicating that the presence of PNH clones augments the odds of possessing cancer-related genetic lesions as early as the time of the initial evaluation. Specifically, patients who were both MN+ and PNH+ were more likely than their PNH- counterparts to have one or two pathogenic and likely pathogenic variants (58.1% vs. 27.3%), though they were equally likely to possess three or more mutations (33.9% vs. 33.3%). Furthermore, among all patients in the cohort ≥70 years, PNH presence significantly increased the overall likelihood of discovering relevant gene variants (78.9% vs. 48.7%, ?2 p= 0.0027).

Among all patients, PNH clone presence was correlated with mutations in SF3B1 (85.7% of cases with SF3B1 variants had PNH clones compared 56.8% of cases with no mutations had PNH clones, Fisher’s exact test, p= 0.0402), and to a lesser degree, with RUNX1 (83.3% PNH+ cases, p= 0.0686) and DNMT3A (80.0% PNH+ cases, p= 0.0914). Finally, we qualitatively described that mutations in ASXL1, TET2, and SRSF2 tended to occur together; there were also concomitant mutations in TET2 with EZH2 and in SF3B1 with RUNX1.

Therefore, we recommend early genetic screening of all elderly patients ≥70 years who present with PNH clones of any size in the peripheral blood as these patients have a higher likelihood of harboring pathogenic and likely pathogenic driver mutations. We demonstrated that certain neoplasm-associated mutations are common in elderly patients, while others correlated with PNH clone presence, and that some variants tend to co-occur. Future studies should address the molecular mechanisms of these lesions in leukemogenesis. The observation that PNH clone presence is significantly correlated with somatic mutations in MN+ disease suggests an important relationship between PNH clones and cancer, either as direct tumor precursor populations or as an incidental consequence of high genetic mutability in a vulnerable bone marrow.

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