Clonal hematopoiesis driven by mutated DNMT3A promotes inflammatory bone loss.

Clonal hematopoiesis of indeterminate potential (CHIP) arises from aging-associated acquired mutations in hematopoietic progenitors, which display clonal expansion and produce phenotypically altered leukocytes. We associated CHIP-DNMT3A mutations with a higher prevalence of periodontitis and gingival inflammation among 4,946 community-dwelling adults. To model DNMT3A-driven CHIP, we used mice with the heterozygous loss-of-function mutation R878H, equivalent to the human hotspot mutation R882H. Partial transplantation with Dnmt3aR878H/+ bone marrow (BM) cells resulted in clonal expansion of mutant cells into both myeloid and lymphoid lineages and an elevated abundance of osteoclast precursors in the BM and osteoclastogenic macrophages in the periphery. DNMT3A-driven clonal hematopoiesis in recipient mice promoted naturally occurring periodontitis and aggravated experimentally induced periodontitis and arthritis, associated with enhanced osteoclastogenesis, IL-17-dependent inflammation and neutrophil responses, and impaired regulatory T cell immunosuppressive activity. DNMT3A-driven clonal hematopoiesis and, subsequently, periodontitis were suppressed by rapamycin treatment. DNMT3A-driven CHIP represents a treatable state of maladaptive hematopoiesis promoting inflammatory bone loss.

Clonal hematopoiesis, somatic mosaicism, and age-associated disease.

Somatic mosaicism, the occurrence of multiple genetically distinct cell clones within the same tissue, is an evitable consequence of human aging. The hematopoietic system is no exception to this, where studies have revealed the presence of expanded blood cell clones carrying mutations in preleukemic driver genes and/or genetic alterations in chromosomes. This phenomenon is referred to as clonal hematopoiesis and is remarkably prevalent in elderly individuals. While clonal hematopoiesis represents an early step toward a hematological malignancy, most individuals will never develop blood cancer. Somewhat unexpectedly, epidemiological studies have found that clonal hematopoiesis is associated with an increase in the risk of all-cause mortality and age-related disease, particularly in the cardiovascular system. Studies using murine models of clonal hematopoiesis have begun to shed light on this relationship, suggesting that driver mutations in mature blood cells can causally contribute to aging and disease by augmenting inflammatory processes. Here we provide an up-to-date review of clonal hematopoiesis within the context of somatic mosaicism and aging and describe recent epidemiological studies that have reported associations with age-related disease. We will also discuss the experimental studies that have provided important mechanistic insight into how driver mutations promote age-related disease and how this knowledge could be leveraged to treat individuals with clonal hematopoiesis.

Clonal Hematopoiesis and Its Impact on Human Health.

Aging is associated with increased mutational burden in every tissue studied. Occasionally, fitness-increasing mutations will arise, leading to stem cell clonal expansion. This process occurs in several tissues but has been best studied in blood. Clonal hematopoiesis is associated with an increased risk of blood cancers, such as acute myeloid leukemia, which result if additional cooperating mutations occur. Surprisingly, it is also associated with an increased risk of nonmalignant diseases, such as atherosclerotic cardiovascular disease. This may be due to enhanced inflammation in mutated innate immune cells, which could be targeted clinically with anti-inflammatory drugs. Recent studies have uncovered other factors that predict poor outcomes in patients with clonal hematopoiesis, such as size of the mutant clone, mutated driver genes, and epigenetic aging. Though clonality is inevitable and largely a function of time, recent work has shown that inherited genetic variation can also influence this process. Clonal hematopoiesis provides a paradigm for understanding how age-related changes in tissue stem cell composition and function influence human health.

Association of clonal hematopoiesis and mosaic chromosomal alterations with solid malignancy incidence and mortality.

BACKGROUND: Understanding the impact of clonal hematopoiesis of indeterminate potential (CHIP) and mosaic chromosomal alterations (mCAs) on solid tumor risk and mortality can shed light on novel cancer pathways. METHODS: The authors analyzed whole genome sequencing data from the Trans-Omics for Precision Medicine Women's Health Initiative study (n = 10,866). They investigated the presence of CHIP and mCA and their association with the development and mortality of breast, lung, and colorectal cancers. RESULTS: CHIP was associated with higher risk of breast (hazard ratio [HR], 1.30; 95% confidence interval [CI], 1.03-1.64; p = .02) but not colorectal (p = .77) or lung cancer (p = .32). CHIP carriers who developed colorectal cancer also had a greater risk for advanced-stage (p = .01), but this was not seen in breast or lung cancer. CHIP was associated with increased colorectal cancer mortality both with (HR, 3.99; 95% CI, 2.41-6.62; p < .001) and without adjustment (HR, 2.50; 95% CI, 1.32-4.72; p = .004) for advanced-stage and a borderline higher breast cancer mortality (HR, 1.53; 95% CI, 0.98-2.41; p = .06). Conversely, mCA (cell fraction [CF] >3%) did not correlate with cancer risk. With higher CFs (mCA >5%), autosomal mCA was associated with increased breast cancer risk (HR, 1.39; 95% CI, 1.06-1.83; p = .01). There was no association of mCA (>3%) with breast, colorectal, or lung mortality except higher colon cancer mortality (HR, 2.19; 95% CI, 1.11-4.3; p = .02) with mCA >5%. CONCLUSIONS: CHIP and mCA (CF >5%) were associated with higher breast cancer risk and colorectal cancer mortality individually. These data could inform on novel pathways that impact cancer risk and lead to better risk stratification.

Clonal hematopoiesis of indeterminate potential and risk of neurodegenerative diseases.

BACKGROUND: Little is known regarding the association between clonal hematopoiesis of indeterminate potential (CHIP) and risk of neurodegenerative diseases. OBJECTIVE: To estimate the risk of neurodegenerative diseases among individuals with CHIP. METHODS: We conducted a community-based cohort study based on UK Biobank and used Cox regression to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for the risk of any neurodegenerative disease, subtypes of neurodegenerative diseases (including primary neurodegenerative diseases, vascular neurodegenerative diseases, and other neurodegenerative diseases), and specific diagnoses of neurodegenerative diseases (i.e., amyotrophic lateral sclerosis [ALS], Alzheimer's disease [AD], and Parkinson's disease [PD]) associated with CHIP. RESULTS: We identified 14,440 individuals with CHIP and 450,907 individuals without CHIP. Individuals with CHIP had an increased risk of any neurodegenerative disease (HR 1.10, 95% CI: 1.01-1.19). We also observed a statistically significantly increased risk for vascular neurodegenerative diseases (HR 1.31, 95% CI 1.05-1.63) and ALS (HR 1.50, 95% CI 1.05-2.15). An increased risk was also noted for other neurodegenerative diseases (HR 1.13, 95% CI 0.97-1.32), although not statistically significant. Null association was noted for primary neurodegenerative diseases (HR 1.06, 95% CI 0.96-1.17), AD (HR 1.04, 95% CI 0.88-1.23), and PD (HR 1.02, 95% CI 0.86-1.21). The risk increase in any neurodegenerative disease was mainly observed for DNMT3A-mutant CHIP, ASXL1-mutant CHIP, or SRSF2-mutant CHIP. CONCLUSION: Individuals with CHIP were at an increased risk of neurodegenerative diseases, primarily vascular neurodegenerative diseases and ALS, but potentially also other neurodegenerative diseases. These findings suggest potential shared mechanisms between CHIP and neurodegenerative diseases.

Clonal Hematopoiesis of Indeterminate Potential and Long-term Outcomes in Heart Transplantation.

BACKGROUND: Clonal hematopoiesis of indeterminate potential (CHIP) mutations, a trait of aging, has been associated with the progression of cardiovascular disease and the development of malignancy. Uncertainty prevails regarding a robust association between CHIP and heart-transplantation (HT) outcomes. OBJECTIVES: To determine the prevalence of CHIP mutations in HT and their association with long-term outcomes, including cardiac allograft vasculopathy (CAV), graft failure, malignancy, and all-cause mortality. METHODS: We conducted a mixed retrospective-prospective observational study of HT recipients with targeted sequencing for CHIP mutations (variant allele frequency [VAF] of ≥ 2%). The primary composite outcome was the first occurrence of CAV grade ≥ 2, graft failure, malignancy, cardiac retransplantation, or all-cause death. Secondary outcomes were the individual components of the composite primary outcome. Sensitivity analyses with base-case and extreme scenarios were performed. RESULTS: Among 95 HT recipients, 30 had CHIP mutations (31.6%). DNMT3A mutations were most common (44.7%), followed by PPM1D (13.2%), SF3B1 (10.5%), TET2 (7.9%), and TP53 (7.9%). The only significant independent predictor of CHIP was age at enrollment or age at transplantation. After multivariable adjustment, CHIP mutations were not associated with the primary outcome, which occurred in 44 (46.3%) patients (HR = 0.487; 95% CI:0.197-1.204; P = 0.119), nor were they associated with mlalignancy alone, or death. CONCLUSION: We demonstrated no association between CHIP mutations and post-transplant outcomes, including CAV, graft failure, malignancy, and all-cause mortality. In line with previously published data, our analysis provides additional evidence about the lack of clinical value of using CHIP mutations as a biomarker for surveillance in outcomes after HT.

The role of clonal progression leading to the development of therapy-related myeloid neoplasms.

Therapy-related myeloid neoplasms (t-MN) are characterized by aggressive features and a dismal prognosis. Recent evidence suggests a higher incidence of t-MN in individuals harboring clonal hematopoiesis of indeterminate potential (CHIP). In order to gain insight into CHIP-driven malignant progression, we gathered data from ten published reports with available detailed patient characteristics at the time of primary malignancy and t-MN development. Detailed clinical and molecular information on primary malignancy and t-MN were available for 109 patients: 43% harbored at least one somatic mutation at the time of the primary malignancy. TET2 and TP53 mutations showed an increasing variant allele frequency from CHIP to t-MN. ASXL1-associated CHIP significantly correlated with the emergence of TET2 and CEBPA mutations at t-MN, as well as U2AF1-driven CHIP with EZH2 mutation and both IDH2 and SRSF2-driven CHIP with FLT3 mutation. DNMT3A-driven CHIP correlated with a lower incidence of TP53 mutation at t-MN. In contrast, TP53-driven CHIP correlated with a complex karyotype and a lower tendency to acquire new mutations at t-MN. Patients with multiple myeloma as their first malignancy presented a significantly higher rate of TP53 mutations at t-MN. The progression from CHIP to t-MN shows different scenarios depending on the genes involved. A deeper knowledge of CHIP progression mechanisms will allow a more reliable definition of t-MN risk.

Clonal Hematopoiesis of Indeterminate Potential Is Associated With Coronary Microvascular Dysfunction In Early Nonobstructive Coronary Artery Disease.

BACKGROUND: Clonal hematopoiesis (CH) of indeterminate potential (CHIP) is a risk factor for cardiovascular disease. The relationship between CHIP and coronary microvascular dysfunction (CMD) is unknown. The current study examines the association between CHIP and CH with CMD and the potential relationships in risk for adverse cardiovascular outcomes. METHODS: In this retrospective observational study, targeted next-generation sequencing was performed for 177 participants with no coronary artery disease who presented with chest pain and underwent routine coronary functional angiogram. Patients with somatic mutations in leukemia-associated driver genes in hematopoietic stem and progenitor cells were examined; CHIP was considered at a variant allele fraction ≥2%; CH was considered at a variant allele fraction ≥1%. CMD was defined as coronary flow reserve to intracoronary adenosine of ≤2. Major adverse cardiovascular events considered were myocardial infarction, coronary revascularization, or stroke. RESULTS: A total of 177 participants were examined. Mean follow-up was 12±7 years. A total of 17 patients had CHIP and 28 had CH. Cases with CMD (n=19) were compared with controls with no CMD (n=158). Cases were 56±9 years, were 68% women, and had more CHIP (27%; P=0.028) and CH (42%; P=0.001) than controls. CMD was associated with independent risk for major adverse cardiovascular events (hazard ratio, 3.89 [95% CI, 1.21-12.56]; P=0.023), and 32% of this risk was mediated by CH. The risk mediated by CH was ≈0.5× as large as the direct effect of CMD on major adverse cardiovascular events. CONCLUSIONS: In humans, we observe patients with CMD are more likely to have CHIP, and nearly one-third of major adverse cardiovascular events in CMD are mediated by CH.

Shared and Reciprocal Mechanisms Between Heart Failure and Cancer　- An Emerging Concept of Heart-Cancer Axis.

Epidemiological evidence of increased risks of cancer in heart failure (HF) patients and HF in cancer patients has suggested close relationships between the pathogenesis of both diseases. Indeed, HF and cancer share common risk factors, including aging and unhealthy lifestyles, and underlying mechanisms, including activation of the sympathetic nervous system and renin-angiotensin-aldosterone system, chronic inflammation, and clonal hematopoiesis of indeterminate potential. Mechanistically, HF accelerates cancer development and progression via secreted factors, so-called cardiokines, and epigenetic remodeling of bone marrow cells into an immunosuppressive phenotype. Reciprocally, cancer promotes HF via cachexia-related wasting and metabolic remodeling in the heart, and possibly via cancer-derived extracellular vesicles influencing myocardial structure and function. The novel concept of the "heart-cancer axis" will help in our understanding of the shared and reciprocal relationships between HF and cancer, and provide innovative diagnostic and therapeutic approaches for both diseases.

Pathophysiology of Acute Myeloid Leukemia.

BACKGROUND: Acute myeloid leukemia (AML) is a biologically heterogenous disease arising in clonally proliferating hematopoietic stem cells. Sequential acquisition of mutations leads to expanded proliferation of clonal myeloid progenitors and failure of differentiation, leading to fulminant AML. SUMMARY: Here, we review the pathophysiology of AML with a focus on factors predisposing to AML development, including prior chemo- and radiation therapy, environmental factors, and germline predisposition. KEY MESSAGE: Increasing genomic characterization of AML and insight into mechanisms of its development will be critical to improvement in AML prognostication and therapy.

Clonal hematopoiesis of indeterminate potential is associated with reduced risk of cognitive impairment in patients with chronic kidney disease.

INTRODUCTION: Clonal hematopoiesis of indeterminate potential (CHIP) and dementia disproportionately burden patients with chronic kidney disease (CKD). The association between CHIP and cognitive impairment in CKD patients is unknown. METHODS: We conducted time-to-event analyses in up to 1452 older adults with CKD from the Chronic Renal Insufficiency Cohort who underwent CHIP gene sequencing. Cognition was assessed using four validated tests in up to 6 years mean follow-up time. Incident cognitive impairment was defined as a test score one standard deviation below the baseline mean. RESULTS: Compared to non-carriers, CHIP carriers were markedly less likely to experience impairment in attention (adjusted hazard ratio [HR] [95% confidence interval {CI}] = 0.44 [0.26, 0.76], p = 0.003) and executive function (adjusted HR [95% CI] = 0.60 [0.37, 0.97], p = 0.04). There were no significant associations between CHIP and impairment in global cognition or verbal memory. DISCUSSION: CHIP was associated with lower risks of impairment in attention and executive function among CKD patients. HIGHLIGHTS: Our study is the first to examine the role of CHIP in cognitive decline in CKD. CHIP markedly decreased the risk of impairment in attention and executive function. CHIP was not associated with impairment in global cognition or verbal memory.

Exploring the Molecular Aspects of Myeloproliferative Neoplasms Associated with Unusual Site Vein Thrombosis: Review of the Literature and Latest Insights.

Myeloproliferative neoplasms (MPNs) are the leading causes of unusual site thrombosis, affecting nearly 40% of individuals with conditions like Budd-Chiari syndrome or portal vein thrombosis. Diagnosing MPNs in these cases is challenging because common indicators, such as spleen enlargement and elevated blood cell counts, can be obscured by portal hypertension or bleeding issues. Recent advancements in diagnostic tools have enhanced the accuracy of MPN diagnosis and classification. While bone marrow biopsies remain significant diagnostic criteria, molecular markers now play a pivotal role in both diagnosis and prognosis assessment. Hence, it is essential to initiate the diagnostic process for splanchnic vein thrombosis with a JAK2 V617F mutation screening, but a comprehensive approach is necessary. A multidisciplinary strategy is vital to accurately determine the specific subtype of MPNs, recommend additional tests, and propose the most effective treatment plan. Establishing specialized care pathways for patients with splanchnic vein thrombosis and underlying MPNs is crucial to tailor management approaches that reduce the risk of hematological outcomes and hepatic complications.

Clonal hematopoiesis of indeterminate potential and outcomes after heart transplantation: A multicenter study.

Cardiac allograft vasculopathy (CAV) is a leading cause of late graft failure and mortality after heart transplantation (HT). Sharing some features with atherosclerosis, CAV results in diffuse narrowing of the epicardial coronaries and microvasculature, with consequent graft ischemia. Recently, clonal hematopoiesis of indeterminate potential (CHIP) has emerged as a risk factor for cardiovascular disease and mortality. We aimed to investigate the relationship between CHIP and posttransplant outcomes, including CAV. We analyzed 479 HT recipients with stored DNA samples at 2 high-volume transplant centers, Vanderbilt University Medical Center and Columbia University Irving Medical Center. We explored the association between the presence of CHIP mutations with CAV and mortality after HT. In this case-control analysis, carriers of CHIP mutations were not at increased risk of CAV or mortality after HT. In a large multicenter genomics study of the heart transplant population, the presence of CHIP mutations was not associated with an increased risk of CAV or posttransplant mortality.

Clonal Hematopoiesis of Indeterminate Potential and Kidney Function Decline in the General Population.

RATIONALE & OBJECTIVE: Clonal hematopoiesis of indeterminate potential (CHIP), defined by the age-related ontogenesis of expanded leukemogenic variants indicative of a genetically distinct clonal leukocyte population, is associated with risk of hematologic malignancy and cardiovascular disease. In experimental models, recapitulation of CHIP promotes kidney interstitial fibrosis with direct tissue infiltration of donor macrophages. We tested the hypothesis that CHIP is associated with kidney function decline in the general population. STUDY DESIGN: Cohort study. SETTING & PARTICIPANTS: 12,004 individuals from 3 community-based cohorts in the TOPMed Consortium. EXPOSURE: CHIP status from whole-genome sequences obtained from DNA extracted from peripheral blood. OUTCOME: Risk of 30% decline in estimated glomerular filtration rate (eGFR) and percent eGFR decline per year during the follow-up period. ANALYTICAL APPROACH: Cox proportional hazards models for 30% eGFR decline end point and generalized estimating equations for annualized relative change in eGFR with meta-analysis. Study-specific estimates were combined using fixed-effect meta-analysis. RESULTS: The median baseline eGFR was 84mL/min/1.73m2. The prevalence of CHIP was 6.6%, 9.0%, and 12.2% in persons aged 50-60, 60-70, and>70 years, respectively. Over a median follow-up period of 8 years, for the 30% eGFR outcome 205 events occurred among 1,002 CHIP carriers (2.1 events per 100 person-years) and 2,041 events in persons without CHIP (1.7 events per 100 person-years). In meta-analysis, CHIP was associated with greater risk of a 30% eGFR decline (17% [95% CI, 1%-36%] higher; P=0.04). Differences were not observed between those with baseline eGFR above or below 60mL/min/1.73m2, of age above or below 60 years, or with or without diabetes. LIMITATIONS: Small number of participants with moderate-to-advanced kidney disease and restricted set of CHIP driver variants. CONCLUSIONS: We report an association between CHIP and eGFR decline in 3 general population cohorts without known kidney disease. Further studies are needed to investigate this novel condition and its potential impact among individuals with overt kidney disease.

Clonal Hematopoiesis: Connecting Aging and Inflammation in Atherosclerosis.

PURPOSE OF REVIEW: Clonal hematopoiesis (CH) is a prevalent condition that results from the acquisition of somatic mutations in hematopoietic stem cells. When these mutations occur in "driver" genes, they can potentially confer fitness advantages to the cell, leading to a clonal expansion. While most clonal expansions of mutant cells are generally considered to be asymptomatic since they do not impact overall blood cell numbers, CH carriers display long-term risks of all-cause mortality and age-associated diseases including cardiovascular disease (CVD). This review summarizes recent findings in CH related to aging, atherosclerotic CVD, and inflammation, emphasizing epidemiological and mechanistic studies, and potential therapeutic options to treat CVDs that are promoted by CH. RECENT FINDINGS: Epidemiological studies have revealed associations between CH and CVDs. Experimental studies with CH models employing the Tet2- and Jak2-mutant mouse lines display inflammasome activation and a chronic inflammatory state that leads to accelerated atherosclerotic lesion growth. A body of evidence suggests that CH represents a new causal risk factor for CVD. Studies also indicate that understanding an individual's CH status could provide guidance for personalized approaches to treat atherosclerosis and other CVDs with anti-inflammatory drugs.

Clonal Hematopoiesis of Indeterminate Potential: Current Understanding and Future Directions.

PURPOSE OF REVIEW: This article summarizes the current knowledge about clonal hematopoiesis of indeterminate potential (CHIP), its association with cardiovascular disease (CVD), and other outcomes, pathogenesis, postulated mechanisms of various pathologies, current knowledge gaps, possible targets of intervention, and therapeutic implications. RECENT FINDINGS: Recently, a common age-related hematological entity known as CHIP has been identified as the independent risk factor for CVD. CHIP is defined as the presence of clonally expanded blood cells involving leukemogenic mutations without the evidence of malignancy. CHIP is known to increase the inflammatory state which in turn is thought to be responsible for increased risk of CVD. Apart from CVD and malignancy, CHIP is also associated with pulmonary embolism, COPD, CKD, stroke, altered metabolism, obesity, liver disease, and increased all-cause mortality. At the same time surprisingly, CHIP is found to have positive outcomes in bone marrow transplant patients and similar reciprocal association with Alzheimer's disease. The risk of CVD and cancer increases with the advancing age, and these two are the leading causes of death in the USA. CHIP is an independent risk factor for CVD development. Most patients with CHIP have somatic clonal mutations in epigenetic regulators, DNA repair genes, or regulatory tyrosine kinases without evidence of overt hematological malignancy. CHIP portends increased risk for leukemia development and carries twofold increased risk of CVD including CAD, MI, and poor prognosis in heart failure. CHIP is associated with various other pathologies making CHIP an area of active research interest in recent years. Current research efforts aim to bridge many knowledge gaps in understanding of CHIP that still exist.

Molecular Studies for the Early Detection of Philadelphia-Negative Myeloproliferative Neoplasms.

JAK2 V617F is the predominant driver mutation in patients with Philadelphia-negative myeloproliferative neoplasms (MPN). JAK2 mutations are also frequent in clonal hematopoiesis of indeterminate potential (CHIP) in otherwise "healthy" individuals. However, the period between mutation acquisition and MPN diagnosis (known as latency) varies widely between individuals, with JAK2 mutations detectable several decades before diagnosis and even from birth in some individuals. Here, we will review the current evidence on the biological factors, such as additional mutations and chronic inflammation, which influence clonal expansion and may determine why some JAK2-mutated individuals will progress to an overt neoplasm during their lifetime while others will not. We will also introduce several germline variants that predispose individuals to CHIP (as well as MPN) identified from genome-wide association studies. Finally, we will explore possible mutation screening or interventions that could help to minimize MPN-associated cardiovascular complications or even delay malignant progression.

[Clonal hematopoiesis: causes and clinical implications]. / Klonale Hämatopoese ­ Ursachen und klinische Implikationen.

Clonal hematopoiesis of indeterminate potential (CHIP) refers to hematopoiesis from stem cells with mutations in leukemia-associated driver genes. These confer increased stress tolerance and expansive potential to stem cell clones. Patients with CHIP are hematologically healthy. The main risk factor for the development of CHIP is age or chronic inflammatory processes associated with aging, so-called "inflammaging". Therefore, the correlation of age-associated comorbidities with the detection of CHIP is not coincidental. CHIP is associated with, among other things, a significantly increased risk of cardiovascular disease and increased all-cause mortality. From a pathomechanistic perspective, CHIP leads to increased secretion of proinflammatory cytokines. It is also associated with a significantly increased risk of developing hematologic neoplasms. Thus, the treatment of CHIP could suppress the occurrence of hematologic neoplasms and prevent age-associated diseases.

Clonal hematopoiesis and cardiovascular disease: deciphering interconnections.

Cardiovascular and oncological diseases represent the global major causes of death. For both, a novel and far-reaching risk factor has been identified: clonal hematopoiesis (CH). CH is defined as clonal expansion of peripheral blood cells on the basis of somatic mutations, without overt hematological malignancy. The most commonly affected genes are TET2, DNMT3A, ASXL1 and JAK2. By the age of 70, at least 20-50% of all individuals carry a CH clone, conveying a striking clinical impact by increasing all-cause mortality by 40%. This is due predominantly to a nearly two-fold increase of cardiovascular risk, but also to an elevated risk of malignant transformation. Individuals with CH show not only increased risk for, but also worse outcomes after arteriosclerotic events, such as stroke or myocardial infarction, decompensated heart failure and cardiogenic shock. Elevated cytokine levels, dysfunctional macrophage activity and activation of the inflammasome suggest that a vicious cycle of chronic inflammation and clonal expansion represents the major functional link. Despite the apparently high impact of this entity, awareness, functional understanding and especially clinical implications still require further research. This review provides an overview of the current knowledge of CH and its relation to cardiovascular and hematological diseases. It focuses on the basic functional mechanisms in the interplay between atherosclerosis, inflammation and CH, identifies issues for further research and considers potential clinical implications.

Driving mosaicism: somatic variants in reference population databases and effect on variant interpretation in rare genetic disease.

BACKGROUND: Genetic variation databases provide invaluable information on the presence and frequency of genetic variants in the 'untargeted' human population, aggregated with the primary goal to facilitate the interpretation of clinically important variants. The presence of somatic variants in such databases can affect variant assessment in undiagnosed rare disease (RD) patients. Previously, the impact of somatic mosaicism was only considered in relation to two Mendelian disease-associated genes. Here, we expand the analyses to identify additional mosaicism-prone genes in blood-derived reference population databases. RESULTS: To identify additional mosaicism-prone genes relevant to RDs, we focused on known/previously established ClinVar pathogenic and likely pathogenic single-nucleotide variants, residing in genes associated with early onset, severe autosomal dominant diseases. We asked whether any of these variants are present in a higher-than-expected frequency in the reference population databases and whether there is evidence of somatic origin (i.e., allelic imbalance) rather than germline heterozygosity (~ half of the reads supporting alternative allele). The mosaicism-prone genes identified were further categorized according to the processes they are involved in. Beyond the previously reported ASXL1 and DNMT3A, we identified 7 additional autosomal dominant RD-associated genes with known pathogenic single-nucleotide variants present in the reference population databases and good evidence of allelic imbalance: BRAF, CBL, FGFR3, IDH2, KRAS, PTPN11 and SETBP1. From this group of 9 genes, the majority (n = 7) was important for hematopoiesis. In addition, 4 of these genes were involved in cell proliferation. Further assessment of the known 156 hematopoietic genes led to identification of 48 genes (21 not yet associated with RDs) with at least some evidence of mosaicism detectable in reference population databases. CONCLUSIONS: These results stress the importance of considering genes involved in hematopoiesis and cell proliferation when interpreting the presence and frequency of genetic variants in blood-derived reference population databases, both public and private. This is especially important when considering new variants of uncertain significance in known hematopoietic/cell proliferation RD genes and future novel gene-disease associations involving this class of genes.