No abstract

Mutational signatures are patterns of somatic alterations in the genome caused by carcinogenic exposures or aberrant cellular processes. To provide a comprehensive workflow for preprocessing, analysis, and visualization of mutational signatures, we created the Mutational Signature Comprehensive Analysis Toolkit (musicatk) package. musicatk enables users to select different schemas for counting mutation types and to easily combine count tables from different schemas. Multiple distinct methods are available to deconvolute signatures and exposures or to predict exposures in individual samples given a pre-existing set of signatures. Additional exploratory features include the ability to compare signatures to the Catalogue Of Somatic Mutations In Cancer (COSMIC) database, embed tumors in two dimensions with uniform manifold approximation and projection, cluster tumors into subgroups based on exposure frequencies, identify differentially active exposures between tumor subgroups, and plot exposure distributions across user-defined annotations such as tumor type. Overall, musicatk will enable users to gain novel insights into the patterns of mutational signatures observed in cancer cohorts. Significance: The musicatk package empowers researchers to characterize mutational signatures and tumor heterogeneity with a comprehensive set of preprocessing utilities, discovery and prediction tools, and multiple functions for downstream analysis and visualization.

We conducted the largest genome-wide association study (GWAS) of Alzheimer’s disease and related dementia (ADRD) in individuals of African-ancestry (AFR) to date using participants from the Million Veteran Program (MVP; 4,012 ADRD cases and 18,435 controls). A proxy GWAS based on survey-reported parental dementia (n=6,641 proxy cases, 45,970 controls) was also performed. The MVP AFR ADRD GWAS and proxy GWAS results were meta-analyzed and combined with the Alzheimer’s Disease Genetics Consortium’s (ADGC) AFR AD GWAS results. The MVP meta-analysis yielded genome-wide significant associations in or near APOE, ROBO1, and RP11-340A13.2. The MVP/ADGC meta-analysis yielded additional genome-wide significant variants near known risk genes TREM2, CD2AP, and ABCA7. We examined differences in expression of the implicated genes in a cohort of AD case and control brains. This study provides insight into dementia pathophysiology in historically understudied individuals of AFR and may help to address health disparities.

BackgroundWhile genome wide association studies (GWASs) of Alzheimer’s Disease (AD) in European ancestry cohorts (EUR) have identified >70 potentially independent AD risk loci, progress in non‐European populations has lagged. In this study, data from US Veterans of African ancestry (AFR) from the Million Veteran Program (MVP) biorepository were used to identify genetic factors associated with AD and related dementias (ADRD).MethodUsing the VA electronic medical record, 4,012 AFR ADRD cases (algorithm includes codes for AD and dementias such as vascular dementia) and 18,435 dementia‐free AFR controls were identified for inclusion in the GWAS. A GWAS was also performed using proxy dementia based on survey‐reported AFR participant parental history of AD or other dementia that included 4,385 maternal cases, 2,256 paternal cases, and 45,970 controls. Meta‐analysis of the case control and proxy results for was performed and then subsequently combined with results from a AFR AD GWAS conducted by the Alzheimer Disease Genetics Consortium (ADGC; Kunkle et al., 2021).ResultThe AFR MVP GWAS (case‐control + proxy) yielded genome‐wide significant associations with several loci including APOE (p=2.48x10‐101), ROBO1 (rs11919682, p=1.63x10‐8), and RP11‐340A13.2 (rs148433063, p=8.56x10‐9. The ROBO1 and RP11‐240A13.2 SNPs were not replicated in the ADGC sample (missing or not significant). The meta‐analysis of MVP and ADGC GWAS results (Table 1) additionally identified genome significant SNPs near known AD risk genes TREM2 (rs73427293, p=2.95x10‐9), CD2AP (rs7738720, p=1.14x10‐9), and ABCA7 (rs73505251, p=3.26x10‐10). Comparison of expression of genes near variants with suggestive evidence of association (p<5x10‐7) in the brains of EUR AD cases and controls from Framingham Heart Study, Religious Orders Study/Rush Memory and Aging Project, Mayo‐Mount Sinai Brain Bank, and Boston University Brain Bank (Panitch et al.) identified several differentially expressed genes including EML6.ConclusionThe AFR dementia GWAS presented here is the largest to date. It increased the number of genome wide significant common‐variant dementia loci reported in AFR cohorts from two to six, including genes previously implicated in EUR cohorts. Increasing representation of AFRs is an important priority in genetic studies and may lead to increased insight into AD pathophysiology and reduce health disparities.

<p>Plate diagram and derivation of bayesian prediction algorithm</p>