PROJECT SUMMARY / ABSTRACT The broad goal of this application is to advance PTSD genetic discovery and address inequity in PTSD genetics research by leveraging a partnership between the Psychiatric Genomics Consortium – Posttraumatic Stress Disorder Working Group (PGC-PTSD) and a network of African investigators, including the Neuropsychiatric Genetics in African Populations (NeuroGAP) program and the Ugandan Genome Resource (UGR). By the end of 2022, the PGC-PTSD will achieve the largest genetic mapping of PTSD to date based on multiethnic meta- analysis of > 1,280,000 samples, leading to 95 risk loci meeting genome-wide significance for PTSD. Beyond discovery, recent work on polygenic risk scores in PTSD shows the potential for the utility of these measures in research. This success is overshadowed, however, by the persistent underrepresentation of African populations in PTSD genetic research, which poses a challenge for both scientific advances in PTSD and global equity. African genomes are characterized by shorter haplotype blocks and contain almost a million more variants per individual than populations outside Africa. The lower correlation between genetic markers in African populations is also useful for fine- mapping disease-causing alleles. However, differences in the African genome also result in limited cross-population transferability of polygenic risk scores, and, by extension, poorer performance in uncharacterized populations such as those from Africa. There is significant risk that the recent advances in PTSD genetics will result in a widening of the massive research and treatment disparities for African populations. This inequity is particularly troubling given the disproportionately high burden of trauma and PTSD faced by African populations both in the US and on the African continent. Thus, data from African populations in genetic studies of PTSD are critical to generate a complete picture of genetic risk factors, identify potentially missing novel therapeutic signals garnered by studying all populations, and address growing health inequity. We propose addressing this inequity by accomplishing the following Specific Aims: (1) Expand the PGC–PTSD sample bank with over 27,000 cases and 112,000 controls from the African continent and diaspora to achieve a robust, well- powered sample size of over 190,000 participants (~39,000 cases, 151,000 controls) with African ancestry; (2) Integrate data across Africa and African diaspora and perform analyses to expand PTSD risk loci discovery; and (3) Leverage African ancestry populations to improve fine-mapping and gene prioritization and to reduce health inequality by improving PRS accuracy for PTSD in these populations. These aims are highly consistent with NIMH Strategic Plan Goal 1, Objective 1.2, Strategy 1.2.A “Discovering gene variances and other genomics elements that contribute to mental illnesses in diverse populations.”