NG00135 – UAB ADRC Genetic Data

The goal of this study is to identify new genes and mutations that cause or increase risk for Alzheimer disease (AD), as well as protective factors. Individuals and families were selected from the Knight-ADRC (Washington University) and the NIA-LOAD study. Only families with at least three first-degree affected individuals were included. Families with pathogenic variants in the known AD or FTD genes, or in which APOE4 segregated with disease were excluded. At least two cases and one control were selected per family. Cases had an age at onset (AAO) after 65 yo and controls had a larger age at last assessment than the latest AAO within the family. Whole exome (WES) and whole genome sequencing (WGS) was generated for 1,235 individuals (285 families) that together with data from our collaborators and the ADSP family-based cohort (3,449 individuals and 757 families) will provide enough statistical power to identify new genes for AD. Dr. Tanzi (Harvard Medical School) will provide WGS from 400 families from the NIMH Alzheimer disease genetics initiative study. We will perform single variant and gene-based analyses to identify genes and variants that increase risk for disease in AD families. Single variant analysis will consist of a combination of association and segregation analyses. We will run family-based gene-based methods to identify genes that show and overall enrichment of variants in AD cases. We will also look for protective and modifier variants. To do this we will identify families loaded with AD cases, that also include individuals with a high burden of known risk variants but that do not develop the disease (escapees). We will use the sequence data and the family structure to identify variants that segregate with the escapee phenotype. The most promising variants and genes will be replicated in independent datasets (ADSP case-control, ADNI, Knight-ADRC, NIA-LOAD ). We will perform single variant and gene-based analyses to replicate the initial findings, and survival analysis to replicate the protective variants. We will select the most promising variants/genes for functional studies

Family-based approaches led to the identification of disease-causing Alzheimer’s Disease (AD) variants in the genes encoding APP, PSEN1 and PSEN2. The identification of these genes led to the A?-cascade hypothesis and to the development of drugs that target this pathway. Recently, we have identified rare coding variants in TREM2, ABCA7, PLD3 and SORL1 with large effect sizes for risk for AD, confirming that rare coding variants play a role in the etiology of AD. In this proposal, we will identify rare risk and protective alleles using sequence data from families densely affected by AD. We hypothesize that these families are enriched for genetic risk factors. We already have sequence data from 695 families (2,462 individuals), that combined with the ADSP and the NIMH dataset will lead to a dataset of more than 1,042 families (4,684 individuals). Our preliminary results support the flexibility of this approach and strongly suggest that protective and risk variants with large effect size will be found, which will lead to a better understanding of the biology of the disease.

We are studying the effects of rare (minor allele frequency < 5%) genetic variants on the risk of developing late-onset Alzheimer’s Disease (AD). We are interested in variants that have a protective effect in subjects who are at an increased genetic risk, or variants that lead to multiple dementias. Our aim is to identify any genetic variants that are present in the “case” group but not the “AD control” groups for both types of variants. The raw data we receive will be annotated to identify SNP locations and frequencies using existing databases such as 1,000 Genomes. We will filter the data based on genetic models such as compounded heterozygosity, recessive and dominant models to identify different types of variants.

Current genetic understanding of Alzheimer’s Disease (AD) does not fully explain its heritability. The APOE4 allele is a well-established risk factor for the development of Alzheimer’s Disease (AD). However, some individuals who carry APOE4 remain cognitively healthy until advanced ages. Additionally, the cause of mixed dementia pathology development in individuals remains largely unexplained. We aim to identify genetic factors associated with these “protected” and mixed pathology phenotypes.

Explore somatic transposable elements and their Alzheimer's disease-related patterns using genomic and phenotypic data from large cohorts:In order to explore the impact of the transposable element in Alzheimer's disease, we propose to conduct a systematic survey in the available large cohorts. The ADSP dataset in NIAGAlzheimer's diseaseS (Accession No. NG00067) includes 16,906 whole-genome sequences and 20,504 whole-exome sequences for case-control and family-based studies of Alzheimer's disease from diverse populations, which is a perfect resource to leverage in this project. Under the support of the Michigan Alzheimer's Disease Center, we will request to access NIAGADS. To detect somatic transposable elements in the ADSP dataset, we will employ established computational pipelines to resolve the transposable elements in the sequencing data, MELT and xTEA for WGS and SCRAMble for WES, respectively. Parameters in these tools, for instance, the calling threshold of supporting reads, will be adjusted accordingly to cooperate with the detection of somatic transposable elements in cells at low frequency. To exclude potential germline transposable elements, we will leverage a master set of polymorphic transposable elements from diverse populations, which are based on our previous projects at the Human Genome Structural Variation Consortium, and the case-control information provided by ADSP. We aim to summarize a spectrum of somatic transposable elements that would be Alzheimer's disease-relevant along with various clinical and phenotypic information. To build Alzheimer's disease-related genetic patterns we will implement Mutect2 (GATK) and Strelka2 to discover SNVs from WGS and WES data and link them with transposable elements in the same haplotype. After obtaining this set of patterns, we will collect phenotypic information from the ADSP dataset to conduct family-based associated analysis and gene-burden analysis. RegulomeDB will be used to annotate the effects of non-coding functional impact and regulatory changes for these Alzheimer's disease-related patterns.

It seeks to explore the connection between the somatic transposable elements in the human genome and Alzheimer’s disease and related dementias. It will leverage large-scale datasets to extensively explore the genome-wide transposable elements and then stratify Alzheimer’s disease-relevant ones by using the rich clinical information from the cohorts. Further analysis pipelines will be built based on the results of the proposed project to investigate the functional impact of these transposable elements on Alzheimer’s disease and would improve the understanding of genetic causes of Alzheimer’s disease and related dementias.