Identity-by-descent (IBD) mapping provides complementary signals to genome-wide association studies (GWAS) when multiple causal haplotypes or variants are present, but not directly tested. However, fa...

Abstract. Homologous long segments along the genomes of close or remote relatives that are identical by descent (IBD) from a common ancestor provide clues

Failing to correct for multiple testing in selection scans can lead to false discoveries of recent genetic adaptations. The scanning statistics in sel…

Identity-by-descent (IBD) mapping provides complementary signals to genome-wide association studies (GWAS) when multiple causal haplotypes or variants are present, but not directly tested. However, failing to correct for multiple testing in case-control studies using IBD segments can lead to false discoveries. We propose the difference between case-case and control-control IBD rates as an IBD mapping statistic. For our hypothesis test, we use a computationally efficient approach from the stochastic processes literature to derive genome-wide significance levels that control the family-wise error rate (FWER). Whole genome simulations indicate that our method conservatively controls the FWER. Because positive selection can lead to false discoveries, we pair our IBD mapping approach with a selection scan so that one can contrast results for evidence of confounding due to recent sweeps or other mechanisms, like population structure, that increase IBD sharing. We developed automated and reproducible workflows to phase haplotypes, call local ancestry probabilities, and perform the IBD mapping scan, the former two tasks being important preprocessing steps for haplotype analyses. We applied our methods to search for Alzheimer's disease (AD) risk loci in the Alzheimer's Disease Sequencing Project (ADSP) genome data. We identified six genome-wide significant signals of AD risk among samples genetically similar to African and European reference populations and self-identified Amish samples. Variants in the six potential risk loci we detected have previously been associated with AD, dementia, and memory decline. Three genes at two potential risk loci have already been nominated as therapeutic targets. Overall, our scalable approach makes further use of large consortia resources, which are expensive to collect but provide insights into disease mechanisms. ### Competing Interest Statement T.A.T. is a current employee of Regeneron Genetics Center and a stockholder of Regeneron Pharmaceuticals. The other authors declare no competing interests. United States Department of Defense, https://ror.org/0447fe631, National Defense Science Engineering Graduate Fellowship Schmidt Sciences, LLC, Eric and Wendy Schmidt AI in Science Postdoctoral Fellowship National Human Genome Research Institute, https://ror.org/00baak391, HG005701 National Institutes of Health, https://ror.org/01cwqze88, U01AG058589, GM081062 National Institute on Aging, https://ror.org/049v75w11, 1R21AG089267

Abstract. RNA viruses like SARS-CoV-2 have high mutation rates, which contribute to their rapid evolution. Mutation rates depend on mutation type and can v

Identity-by-descent (IBD) is used to infer malaria parasite population demography, but positive selection imposed by drug pressure can bias IBD estimates. This study shows that strong selection distor...

Calculate IBD segments from tree sequence using tskit C API - bguo068/tskibd

The worst-case runtime complexity to simulate haplotype segments identical by descent (IBD) is quadratic in sample size. We propose two main techniques to reduce the compute time, both of which are mo...