OBJECTIVE:Exome sequencing (ES) detects a monogenic disorder in approximately 30% of pregnancies with unexplained nonimmune hydrops fetalis spectrum (NIHFS), defined as the presence of one or more pathologic fetal fluid collection. Since genome sequencing (GS) can identify additional genetic variants not detectable by ES, we sought to determine the proportion of cases with new reportable findings on GS following nondiagnostic standard of care testing, including ES, for NIHFS. STUDY DESIGN:Cohort study of pregnancies with NIHFS that had nondiagnostic results of karyotype and/or chromosomal microarray analysis (CMA) and ES. Eligible fetal fluid collections included at least one of: ascites, pleural or pericardial effusions, skin edema, cystic hygroma, and/or nuchal translucency ≥3.5 mm. Pregnancies with NIHFS that did not receive a clear diagnosis with prior testing underwent additional testing with GS. ES and GS were performed in a Clinical Laboratory Improvement Amendments-approved laboratory, and genetic variants were classified according to the American College of Medical Genetics and Genomics guidelines. Primary outcome was the proportion of new reportable pathogenic or likely pathogenic (P/LP) variants identified on GS and resulting in a new diagnosis. Secondary outcome was the incremental yield of GS for detecting new secondary findings and variants of uncertain significance (VUSs). RESULTS:Overall, 118 fetal samples underwent GS following negative (n=102) or inconclusive (n=16) ES. GS identified four P/LP copy number variants previously not detected by karyotype, CMA, or ES that led to a new genetic diagnosis in three pregnancies, providing a new positive finding yield of 2.5% (3/118). Additionally, one secondary finding and four VUSs were identified by GS in four different pregnancies. In contrast to the primary outcome, these additional findings were largely the result of updated analytical tools and literature rather than GS-specific technology. CONCLUSION:GS has a small but clinically relevant increased diagnostic yield over chromosome studies and ES for NIHFS, particularly for identifying copy number variants. As interpretation of noncoding regions and complex genomic variations improves, the incremental positive finding yield of GS is expected to further increase.

Pathogenic DEGS1 variants have been reported in individuals with autosomal recessive hypomyelinating leukodystrophy 18 (HLD18; MIM# 618404). Here we describe three participants with HLD features and a previously unreported homozygous DEGS1 5′ splice site variant, c.825+4_825 + 5delAGinsTT (NM_003676.4). We used next-generation DNA and transcriptome sequencing, cell-based splicing assays, and tandem mass spectrometry to detect and characterize the variant’s impact on DEGS1 expression. We then performed RNA structure probing and conventional antisense oligonucleotide screening to investigate molecular mechanisms for potential therapeutic intervention. We show that the splice site variant: (1) was sufficient to induce exon two skipping in most detected transcripts; (2) resulted in structural changes to the 5′ and 3′ splice site regions using RNA structure probing; and (3) corresponds to plasma sphingolipid profiles consistent with loss of sphingolipid delta(4)-desaturase activity. Our RNA and lipidomic evidence proved that the DEGS1 variant c.825+4_825 + 5delAGinsTT is pathogenic and suggested a mechanistic model that explains how exon two skipping is induced.

Abstract Background: Molecular profiling of meningioma has revealed biologic drivers and therapeutic vulnerabilities that have refined risk stratification and guided clinical trials. Most molecular studies of meningioma are limited to retrospective cohorts, and the population prevalence of meningioma genomic alterations is incompletely understood. Methods: DNA mutations and copy number alterations (CNAs) were defined across a consecutive cohort of 1,104 meningiomas that were prospectively analyzed using the next-generation UCSF500 DNA sequencing assay at a single institution from 2019 to 2025. Results: Meningiomas were CNS WHO grade 1 (49.4%), grade 2 (30.9%), grade 3 (7.0%), or undefined (12.7%). Median patient age was 60 years (range 2-91) and 64.1% were female. Patient race included white (39.2%), Asian (10.4%), Black or African American (3.6%), Native American or Alaska Native (0.6%), Native Hawaiian (0.3%), other Pacific Islander (0.3%), other (9.5%), or unknown. Ethnicity was reported as Hispanic or Latino in 125 cases (11.3%). Loss of chromosomes 22q (64.1%), 1p (40.7%), and 14q (22.3%) were the most common CNAs. Multivariate regression identified male sex, increasing age, and Asian vs. white race as significant predictors of multiple CNAs that are associated with poor clinical outcomes, including co-occurrent 1p loss/1q gain (odds ratio [OR] for male sex: 2.79, p<0.001; increasing age OR 1.02, p=0.028; Asian vs. white race OR 2.77, p=0.001). CNA burden was enriched in high grade meningiomas (p<0.001), and male sex (OR 10.1, p<0.001), increasing age (OR 1.04, p=0.026), and Asian vs. white race (OR 4.31, p=0.047) were significant predictors of higher CNA burden. The most common short somatic variants (SSVs) were in NF2 (53.6%) and TRAF7 (16.3%), which were mutually exclusive in all but 2 meningiomas. CDKN2A/B homozygous deletions and TERT promoter mutations were identified in 3.1% and 3.6% of meningiomas, respectively. Increasing age was a significant predictor of NF2 (OR 1.02, p<0.001) and TERT promoter mutation (OR 1.06, p=0.001), and Asian vs. white race was a significant predictor of CDKN2A/B mutation (OR 4.26, p=0.003). Median tumor mutation burden (TMB) was 3.4/megabase. Mutations in ARID1A (p<0.001), ARID2 (p=0.028), CDKN2A/B (p=0.017), KMT2D (p=0.011), SMARCB1 (p=0.0061), TERT (p<0.001), TET2 (p=0.019), and TP53 (p=0.0033) were associated with elevated TMB. Increasing age (OR 1.01, p=0.02) and Asian (OR 5.02, p<0.001) and Black (OR 2.54, p=0.004) vs. white race were significant predictors of higher TMB. Conclusion: Prospective next-generation DNA sequencing of consecutive meningiomas defines the population prevalence of molecular alterations. These data fill a critical gap in the understanding of biological drivers of meningioma behavior and therapeutic response across demographic groups. Citation Format: Minh P. Nguyen, Kanish Mirchia, Brooke C. Braman, Ramin A. Morshed, Nancy Ann Oberheim Bush, Javier E. Villanueva-Meyer, William C. Chen, Walter Patrick Devine, Arie Perry, David R. Raleigh. Genomic profiling of 1,104 consecutive, prospective meningiomas defines the population prevalence of molecular alterations and elucidates potential biomarkers of treatment response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 1979.

Pseudouridylation is a frequent post-transcriptional modification resulting in uridine isomerization in 5-ribosyluracil, also called pseudouridine. This mechanism leads to RNA stability with an increase in base-stacking and the creation of hydrogen bonds. Recently, papers reported that variants in PUS7 in 16 patients were involved in marked growth retardation with microcephaly, associated with intellectual disability and behavioral issues such as self-injurious and aggressive behavior. Through Genematcher, we initiated a collaboration to describe a new cohort of PUS7 patients. In total, we report 13 new cases carrying 15 new variants. This cohort further expands the phenotypic spectrum associated with PUS7-related syndromes, allowing for improved genotype-phenotype correlations and ultimately better healthcare for affected individuals and their families.

7016 Background: CNS relapse of DLBCL is a devastating event with median survival <6 months. While the overall incidence is low (~5%), various factors impact the risk of CNS relapse including CNS-IPI, cell-of-origin (COO), and MYC rearrangement. Recent studies using NGS have defined DLBCL genetic subgroups with distinct biology. The MCD and C5 subgroups, defined by LymphGen and DLB class , respectively, have a shared genetic signature characterized by MYD88 L265P and CD79B mutations, immune evasion, and extranodal tropism with enrichment in CNS lymphomas. We investigated the impact of MCD/C5 signature on the risk of CNS relapse in a large cohort of DLBCL patients (pts) profiled with NGS. Methods: We performed a retrospective analysis of 155 DLBCL pts treated with chemoimmunotherapy and profiled with the UCSF500 NGS panel, which includes 529 genes and copy number data. FISH was performed to evaluate for MYC , BCL2 and BCL6 rearrangements. Pts with CNS involvement at diagnosis were excluded. Data were extracted from medical records including demographics, WHO-HAEM5 diagnosis, COO per Hans algorithm, CNS-IPI, and treatment history. LymphGen and DLB class subtypes were determined using online classifiers incorporating NGS and FISH data. We identified LymphGen and DLB class subtypes enriched in pts with CNS relapse. We performed univariable and multivariable analysis (MVA) (Cox proportional hazards model) to assess the impact of COO, CNS-IPI, and genetic signature on the cumulative incidence (CI) of CNS relapse. Results: The median age was 61. 60% were male, 57% non-Hispanic white, 21% Asian, 16% Hispanic, and 3% Black. DLBCL subgroups included DLBCL-NOS (60%), transformed DLBCL (15%), Richter transformation (8%), high-grade B-cell lymphoma (HGBCL)-double hit (5%), primary mediastinal LBCL (4%), DLBCL, post-transplant (3%), HGBCL-NOS (3%), and T-cell histiocyte-rich LBCL (2%). 67% were stage III-IV, 51% non-GCB type, and 21% high-risk CNS-IPI. LymphGen subtypes included EZB-MYC- (26%), ST2 (12%), MCD (9%), EZB-MYC+ (7%), BN2 (7%), N1 (3%), and composite cases (3%); 34% were unclassifiable. DLB class subtypes included C1 (13%), C2 (3%), C3 (52%), C4 (8%), and C5 (11%); 14% were not classified given <50% confidence in assignment. Median follow-up was 30 months. 18 pts experienced CNS relapse; these cases were enriched for MCD and C5 subtypes (28% each). The 2-year CI of CNS relapse in pts with MCD and/or C5 subtypes (N=21) was 20.4% vs. 6.4% in non-MCD/C5 cases (HR 3.46, p=0.007). Notably, 3 MCD/C5 pts had late CNS relapse (>3 years from diagnosis). In MVA, MCD/C5 signature was an independent risk factor for CNS relapse (HR 4.51, 95% CI 1.42-14.32, p=0.011) along with MYC rearrangement (p=0.036) and non-GCB COO (p=0.028). Conclusions: In this heterogeneous DLBCL cohort, MCD/C5 genetic signature was an independent risk factor for CNS relapse. Incorporation of CNS-active agents should be prioritized for this subgroup.

PURPOSE:SET is a member of the inhibitor of histone acetyltransferases complex involved in transcriptional silencing and gene regulation. Pathogenic variants in SET are postulated to cause neurodevelopmental disorder (NDD) phenotypes, but as only a few individuals are described, detailed clinical information is scarce. Hence, currently, counseling on phenotypes and prognosis of this condition remains challenging. METHODS:Here, we describe the clinical phenotype and mutational spectrum of 23 unreported individuals harboring (likely) pathogenic variants in SET. RESULTS:Phenotypes include global developmental delay, often with pronounced hypotonia, delayed motor development, and speech and language delay, ultimately evolving into (mild) intellectual disability. Comorbidities include behavioral concerns, sleep disturbances, and variable nonspecific ocular problems. Next-generation computer-assisted phenotyping using GestaltMatcher showed limited overlapping facial features between affected individuals and differences compared with disorders caused by related chromatin-modifying genes in individuals. In addition, we generated a DNA methylation signature able to distinguish individuals carrying pathogenic variants in SET from individuals with other neurodevelopmental disorders and healthy controls. We used this DNA methylation signature to assess the pathogenicity of 2 variants of uncertain clinical significance in SET found in 2 additional individuals. CONCLUSION:Together, this expands the knowledge on SET-related disorders and provides novel approaches for their diagnosis.

Abstract The determination of the genetic subtypes of primary central nervous system lymphoma (PCNSL) and their relationship to differential chemoimmunotherapeutic response has not been established. There is a particular need for genomic biomarkers that identify patients with newly diagnosed PCNSL at high risk of early progression and death. We applied targeted next-generation sequencing for detection of recurrent single-nucleotide variants, copy number alterations, and zygosity abnormalities in diagnostic specimens from 78 patients with PCNSL treated with a standard methotrexate-based regimen, to identify prognostically significant molecular subgroups. All patients received induction immunochemotherapy, and 44 proceeded to dose-intensive consolidation. Genomic aberrations at 4 loci were associated with 91% of lymphoma progression events and all 15 deaths: (1) chromosome 6p copy-neutral loss of heterozygosity (CN-LOH) or focal homozygous deletion (HD) at 6p21.3, and mutations of tumor suppressor genes (2) BTG1, (3) ETV6, and (4) TP53. Cox regression multivariate analysis demonstrated a high risk of progression in patients with aberrations at these loci. Genomic aberrations at these loci were also associated with significantly shorter survival. Lower expression of HLA-DR was associated with 6p CN-LOH/6p21.3 HD and inferior prognosis. These genomic aberrations identify a high-risk molecular subgroup that may inform risk stratification in PCNSL. Further elucidation of the mechanisms of therapeutic resistance associated with the high-risk genetic phenotype is requisite to facilitate precision medicine and progress in therapy.

OBJECTIVE:We describe a series of pregnancies with autosomal dominant lymphedema and generalized lymphatic dysplasia in the fetus diagnosed with prenatal exome or genome sequencing. We focus on specific syndromes, fetal features, and parental symptoms to deepen our understanding of congenital lymphatic anomalies. METHODS:Pregnancies with one or more fetal effusions were prospectively enrolled from 2017 to 2024 and underwent exome or genome sequencing. Fetal effusions included increased nuchal translucency ≥ 3.5 mm, cystic hygroma, pleural effusion, pericardial effusion, ascites, and/or skin edema. Records were reviewed to extract personal and family history, ultrasound findings, and pregnancy outcomes. RESULTS:Among 303 pregnancies with one or more fetal effusions, eight (3%) had a molecular diagnosis of autosomal dominant lymphedema or generalized lymphatic dysplasia. Gestational age at detection of fetal effusion(s) ranged from the first through third trimesters. Four fetuses inherited the genetic variant(s) from a biological parent. Of these, one parent was asymptomatic, and three had largely milder symptoms than their fetus. Perinatal outcomes were more favorable for fetuses with heterozygous PIEZO1 variants. CONCLUSION:Autosomal dominant lymphedema and generalized lymphatic dysplasia can present with a breadth of fetal effusions from the first through third trimesters and are frequently inherited from a biological parent with less severe symptoms. These data provide a deeper understanding of how congenital lymphatic anomalies manifest in utero and inform expectations about recurrence risk in future pregnancies.

OBJECTIVES:Nonimmune hydrops fetalis is well understood to be heterogenous and the common endpoint of many genetic diseases. However, less is known about the prevalence and presenting features of genetic diseases that underlie other types of fetal effusions such as single effusions, leaving uncertainty in clinical practice about optimal approaches to testing and counseling for these pregnancies. We aimed to determine the diagnostic yield of exome sequencing by type of fetal effusion and presence of concurrent structural abnormalities and to identify the unique presenting features of underlying genetic diseases. STUDY DESIGN:We conducted a prospective cohort study of pregnancies with nonimmune hydrops fetalis and other fetal effusions, with participants enrolled from across the United States. Inclusion criteria were nondiagnostic results of chromosomal microarray and/or karyotype and the presence of at least 1 fetal effusion, including nuchal translucency ≥3.5 mm, cystic hygroma, pleural effusion, pericardial effusion, ascites, and/or skin edema. Exome sequencing was performed by our institution's Clinical Laboratory Improvement Amendments-approved laboratory and results were returned to participants and their providers. Detailed fetal phenotypic data were ascertained and used to inform genetic variant interpretation, including fetal imaging findings (ultrasound, magnetic resonance imaging, and echocardiogram), pathology reports, and laboratory reports. Pregnancies with a variant or variants classified as pathogenic or likely pathogenic were considered diagnostic or positive. The primary outcome was the diagnostic yield of exome sequencing by the type of fetal effusion, with and without concurrent structural abnormalities. Secondary outcomes were the types of fetal effusions observed by category of genetic disease. RESULTS:In all, 118 pregnancies with nonimmune hydrops fetalis and other effusions underwent exome sequencing and 23% (27/118) had positive (diagnostic) findings. Pregnancies with nonimmune hydrops fetalis with and without concurrent structural abnormalities had diagnostic yields of 21% (9/42) and 40% (6/15), respectively (P=.15). Single effusions such as pleural effusion with and without concurrent structural abnormalities had diagnostic yields of 23% (6/26) and 17% (1/6), respectively (P=.61). The diagnostic yield for increased nuchal translucency or cystic hygroma was significantly greater for pregnancies with concurrent structural abnormalities (42%, 5/12) compared to those without (0%, 0/17, P<.01). We further observed numerous patterns in terms of how genetic diseases present in utero, such as RASopathies and musculoskeletal disorders demonstrating all types of effusions, while other disorders marked by neurodevelopmental delays after birth demonstrated all types of effusions except for nonimmune hydrops fetalis. CONCLUSION:The diagnostic yield of exome sequencing was high across all types of effusions including single effusions with and without concurrent structural abnormalities, with the exception of isolated increased nuchal translucency or cystic hygroma. Furthermore, we observed numerous patterns in terms of how genetic diseases present in utero with fetal effusions. These findings contribute important information for counseling and clinical management, highlight the utility of exome sequencing for fetal effusions beyond nonimmune hydrops fetalis, and inform accurate results of phenotype-driven tests such as exome sequencing.

Failure of septation of the interventricular septum (IVS) is the most common congenital heart defect, but mechanisms for patterning the IVS are largely unknown. Here we show that a Tbx5+/Mef2cAHF+ progenitor lineage forms a compartment boundary bisecting the IVS. This coordinated population originates at a first and second heart field interface. Ablation of Tbx5+/Mef2cAHF+ progenitors causes IVS disorganization, right ventricular hypoplasia and mixing of IVS lineages. Reduced dosage of the congenital heart defect transcription factor TBX5 disrupts boundary position and integrity, resulting in ventricular septation defects and patterning defects, including misexpression of Slit2 and Ntn1, which encode guidance cues. Reducing NTN1 dosage partly rescues cardiac defects in Tbx5 mutant embryos. Loss of Slit2 or Ntn1 causes ventricular septation defects and perturbed septal lineage distributions. Thus, we identify Tbx5 as a candidate selector gene, directing progenitors and regulating essential cues, to pattern a compartment boundary for proper cardiac septation, revealing mechanisms for cardiac birth defects.

ABSTRACTPrenatal exome sequencing (ES) can establish rare genetic diagnoses in a fetus but may also lead to occult genetic diagnosis in a biological parent. We present a case of dual fetal and maternal diagnosis by prenatal ES, in a fetus with unexplained anemia and in a pregnant patient with sickle cell disease (SCD) and recurrent unexplained hypoxia. ES identified a novel, likely pathogenic gamma globin variant, HbF Mission Bay HBG2 (c.86T > A, p.Leu29Gln), in both the fetus and mother. Deleterious variants in HBG2 have been associated with cyanosis, hypoxia, methemoglobinemia, and hemolytic anemia that are typically confined to infancy. In the pregnant patient who herself had a separate diagnosis of SCD, the HBG2 variant manifested with hypoxia as an infant herself, recurrent hypoxia in adulthood, and methemoglobinemia during pregnancy due to persistence of HbF. This same variant manifested in the fetus as anemia requiring multiple in utero transfusions as well as neonatal methemoglobinemia after birth.

Objective This article describes the implementation of preemptive clinical pharmacogenomics (PGx) testing linked to an automated clinical decision support (CDS) system delivering actionable PGx information to clinicians at the point of care at UCSF Health, a large Academic Medical Center.Methods A multidisciplinary team developed the strategic vision for the PGx program. Drug-gene interactions of interest were compiled, and actionable alleles identified. A genotyping platform was selected and validated in-house. Following HIPAA protocols, genotype results were electronically transferred and stored in electronic health records (EHRs). CDS was developed and integrated with electronic prescribing.Results We developed a customized PGx program for 56 medications and 15 genes. Two hundred thirty-three pharmacogenomic prescribing alerts and 15 pharmacogenomic testing prompts, approved by clinicians, were built into EHR to deliver actionable clinical PGx information to clinicians.Conclusions Our multidisciplinary team successfully implemented preemptive PGx testing linked to point-of-care CDS to guide clinicians with precise medication decision-making.

Molecular profiling of meningioma has revealed biologic drivers and therapeutic vulnerabilities that have refined risk stratification and guided clinical trials. Most molecular studies of meningioma are limited to retrospective research cohorts, and the population prevalence of meningioma genomic alterations is incompletely understood. Here we define DNA mutations and copy number alterations (CNAs) across a consecutive cohort of 1,104 meningiomas that were prospectively analyzed using the next-generation UCSF500 DNA sequencing assay from 2019 to 2025. Median patient age was 60 years (range 2-91) and 64.1% were female. Meningiomas were CNS WHO grade 1 (56.6%), 2 (35.4%), or 3 (8.0%). Loss of chromosomes 22q (63.2%), 1p (40.3%), and 14q (22.0%) were the most common CNAs. CNA burden was associated with higher WHO grade (p<2.2e-16). The most common somatic mutations were in NF2 (53.6%) and TRAF7 (16.3%), which were mutually exclusive in all but 2 meningiomas. AKT1 or KLF4 were co-mutated in 58.9% of TRAF7-mutant meningiomas. CDKN2A/B homozygous deletions and TERT promoter mutations were identified in 3.1% and 3.6%, respectively. 25.2% of meningiomas had no detected CNAs, 13.2% lacked somatic mutations, and 2.6% had no mutations or CNAs. Correlation analyses revealed novel co-mutated genes like BCORL1 and SPEN (co-mutated in 0.5%), and co-occurrent CNAs like loss of 12p and 17p (1.5%). Median tumor mutation burden (TMB) was 3.4/megabase. Mutations in ARID1A (p=6.9e-05), ARID2 (p=0.028), CDKN2A/B (p=0.017), KMT2D (p=0.011), SMARCB1 (p=0.0061), TERT (p=0.00057), TET2 (p=0.019), and TP53 (p=0.0033) were associated with elevated TMB, an emerging predictor of meningioma response to immune checkpoint inhibition. At least one gene associated with elevated TMB was mutated in 13.8% of meningiomas in the absence of mismatch repair deficiency, which was identified in only 1.0%. In conclusion, prospective next generation DNA sequencing of consecutive meningiomas defines the population prevalence of molecular alterations and elucidates potential biomarkers of treatment response.

It has been suggested that diagnostic yield (DY) from Exome Sequencing (ES) may be lower among patients with non-European ancestries than those with European ancestry. We examined the association of DY with estimated continental/subcontinental genetic ancestry in a racially/ethnically diverse pediatric and prenatal clinical cohort. Cases (N = 845) with suspected genetic disorders underwent ES for diagnosis. Continental/subcontinental genetic ancestry proportions were estimated from the ES data. We compared the distribution of genetic ancestries in positive, negative, and inconclusive cases by Kolmogorov–Smirnov tests and linear associations of ancestry with DY by Cochran-Armitage trend tests. We observed no reduction in overall DY associated with any genetic ancestry (African, Native American, East Asian, European, Middle Eastern, South Asian). However, we observed a relative increase in proportion of autosomal recessive homozygous inheritance versus other inheritance patterns associated with Middle Eastern and South Asian ancestry, due to consanguinity. In this empirical study of ES for undiagnosed pediatric and prenatal genetic conditions, genetic ancestry was not associated with the likelihood of a positive diagnosis, supporting the equitable use of ES in diagnosis of previously undiagnosed but potentially Mendelian disorders across all ancestral populations.

Introduction: Clonal hematopoiesis of indeterminate potential (CHIP) has been associated with an increased risk of coronary artery disease (CAD) and cardiovascular (CV) mortality. Whether CHIP may affect myocardium beyond promoting CAD, or its potential association with sudden cardiac death (SCD), the most feared manifestation of CV disease, is unknown. Research Questions/Hypothesis: We hypothesize that CHIP-mutant macrophages infiltrate the myocardium and are associated with autopsy-defined arrhythmic death. Goals/Aims: (1) determine rate of CHIP at time of death in an unselected, countywide study of all incident sudden deaths; (2) evaluate whether CHIP-mutant macrophages infiltrate into myocardium; and (3) evaluate potential association of CHIP with autopsy-confirmed arrhythmic causes among countywide sudden deaths Methods/Approach: We used autopsy to adjudicate arrhythmic from non-arrhythmic (PE, stroke, overdose, tamponade) causes in 1,148 sudden deaths and 141 trauma control deaths in San Francisco County from 2011-23. DNA was extracted from frozen blood samples collected at time of death from 399 consented cases. Sequencing of 22 CHIP-associated genes was performed to ~2000x mean target coverage. All pathogenic/likely pathogenic CHIP variants at >2% variant allele frequency (VAF) were considered CHIP+. DNA was then isolated from left ventricular (LV) tissue sampled at autopsy in all CHIP+ blood cases and sequenced as above. Results: Of 399 consented cases, 70 blood samples (17.5%) were CHIP+ (range 2%-39.6%; mean age 70.6 years vs. 58.1 years for CHIP-). The most frequent mutant genes were DNMT3A, TET2, and ASXL1. Proportion of arrhythmic causes among sudden deaths was similar for CHIP+ vs. CHIP- cases (36 of 70 [52%] vs. 171 of 329 [51%]). Sequencing of available LV tissue from 61 CHIP+ blood cases revealed 67% (n=41) harbored the same CHIP mutation identified in blood at >0.2% VAF (range 0.2%-4.3%). Proportion of arrhythmic causes among sudden deaths was significantly higher in cases where both blood and LV were CHIP+ (24 of 41 [58.5%] vs. 5 of 19 [26.3%] CHIP+ blood/CHIP- LV, p=0.02). Conclusions: Prevalence of CHIP positivity at sudden death is similar to published studies and correlated with age. CHIP+ status in myocardial tissue but not peripheral blood was associated with arrhythmic causes of sudden death, suggesting a direct tissue effect of CHIP-mutant macrophages.