NCT00001174 Starting in 1993, in collaboration with 10 academic centers across the US, we recruited a large sample of over 3,000 individuals with bipolar or other mood disorders. All participants did a diagnostic interview and provided a blood sample for DNA analysis. DNA and clinical data are available through the NIMH Center for Genetics. Genetic linkage studies suggested several chromosomal regions may contain genes that contribute to mood disorders in this sample. To identify individual causal genes, we conducted the first genome-wide association study (GWAS) of bipolar disorder (BD) in 2007. The results implicated several genes, each of small effect, suggesting that BD is a polygenic disease. A second, larger study published in 2010 implicated a cluster of genes on chromosome 3p21 and suggested genetic overlap with major depression. An even larger study published in 2013 that included patients of Asian ancestry supported many of the previous findings and found 3 additional genetic markers of BD. Most of these findings have now been replicated in independent samples. To identify additional risk loci, last year we performed a meta-analysis of >9 million genetic variants in over 40,000 individuals, the largest published GWAS of BD to date. To increase power, we used 2,000 lithium-treated cases with a long-term diagnosis of BD from the Consortium on Lithium Genetics, excess controls, and analytic methods optimized for markers on the X-chromosome. In addition to 4 known loci, we identified 2 novel loci. Our results added to a growing list of common variants involved in BD. We also contributed genotype data from about 1000 cases to the Psychiatric Genomics Consortium Bipolar Disorder Workgroup, where they were combined with another 30,000 cases and controls. Preliminary results implicate 30 independent genetic markers for BD, 20 of which have not been previously associated with BD. These large GWAS also provide a valuable set of reference data for calculating polygenic risk scores (PRS) that capture the combined influence of many alleles of small effect. We are exploring ways in which the PRS can be used to better understand individual differences in the onset, course, and presentation of BD. Recently, we used PRS to address the high rates of comorbid anxiety in bipolar disorder, a largely unexplained phenomenon. Does this comorbidity reflect shared genetic risk? Preliminary results show that among individuals with BD, genetic risk for anxiety is associated with comorbid anxiety disorders, recurrent suicide attempts, and increased adverse events during lithium therapy. Surprisingly, genetic risk for bipolar disorder itself was not related to any of these variables. In other samples, anxiety showed more genetic overlap with depression, neuroticism, and respiratory conditions than with bipolar disorder. These findings suggest that comorbid anxiety in BD reflects largely distinct contributions of bipolar and anxiety-related genes. Treatments that address this dual genetic burden may improve outcomes in people with this common comorbidity. To identify rarer genetic variants that may have a larger impact on risk for major mood disorders, we have undertaken genome sequencing studies in families and special populations. So far, we have collected more than 800 individuals from Amish and Mennonite communities whose unique genetic history makes them especially good candidates for this kind of study. All blood samples are processed by the Rutgers Cell and DNA Repository, which also establishes lymphoblastoid cell lines and distributes DNA as a resource for the general scientific community. In addition to standard psychiatric diagnostic assessments, participants are asked to complete measures of memory, concentration, and other cognitive domains, along with dimensional measures of mood and anxiety. These data will allow us to better characterize the range of phenotypes present in carriers of risk alleles, many of whom are not expected to have diagnosable mental illness. Through a collaboration with investigators at the Univ Maryland, we will also investigate brain connectivity in selected cases, using multi-modal neuroimaging. Skin biopsies are obtained on sequenced individuals and converted to fibroblasts. Several fibroblast lines have been reprogrammed into induced pluripotent stem cells for functional genomic studies (see ZIA-MH002810-15). In collaboration with investigators at Regeneron, Inc., we have performed exome sequencing on over 800 participants. Preliminary analyses have identified a number of otherwise rare genetic variants that occur much more frequently in participants with a history of BD or a related mental illness. With this data set, we are able to look for recurrent rare mutations, as well as mutations that have accumulated within individual genes and gene-sets. The current sample size is well powered to detect variants that confer substantial risk for BD. If such variants are not detected, larger samples will be needed to detect variants that confer more modest risk of illness. The exome data are being submitted to the Bipolar Sequencing Consortium, where they will become part of a large meta-analysis that brings together samples from many groups around the world in order to improve statistical power to detect variants of modest effect. In collaboration with investigators at the Univ Pennsylvania, Univ Miami, Case Western Reserve, and Univ Kansas, we have also performed whole-genome sequencing on a larger set of individuals ascertained from Amish and Mennonite communities. The goal was to develop a population specific reference panel (the Anabaptist Genome Reference Panel or AGRP) that will allow us to infer rare genetic variants in individuals who have not undergone whole genome sequencing, thus increasing sample size at greatly reduced cost. Phase I of the AGRP was completed last year. We have set up an imputation server so outside researchers working with Anabaptist populations can use the AGRP to impute rare alleles in their own samples. We are also searching for genetic markers that help predict response to lithium, one of the most effective treatments for BD. In collaboration with Univ Bonn, we did genome-wide genotyping on over 3000 cases. Confirmed biomarkers of lithium response would be an important step forward in the care of people with BD. We organized a large international collaboration, known as the Consortium on Lithium Genetics (ConLiGen), aimed at characterizing lithium response in large groups of patients using reliable instruments, followed by GWAS. We found 4 markers in the same region on chromosome 21 that were associated with lithium response and supported by study in an independent sample. Subsequent analyses in this dataset demonstrated that common genetic variants associated with schizophrenia predicted poorer response to lithium and, in joint analyses, implicated additional genetic loci harboring variants involved in both lithium response and schizophrenia risk. This year we went one step further and integrated the lithium response data with the results of large-scale studies of the relationship between common genetic variation and gene expression, such as GTEX. Preliminary results highlight genes in the HLA region, known for its role in modulating immune response. In the coming year, we will seek to replicate and extend these findings in additional samples. We expect to enroll an additional 100 participants in the exome sequencing study, complete additional sequencing, and reprogram additional tissue samples. We will also perform heritability analyses that will inform case definitions that will be used in genetic analyses of identified rare variants.
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