PROJECT SUMMARY Non-alcoholic fatty liver disease (NAFLD), caused by excess accumulation of fat in the liver (steatosis), has a global prevalence of 25.2% and is the most common cause of chronic liver disease worldwide. There are few effective ways to prevent or treat NAFLD making it one of the biggest unmet public health needs of our time. A better understanding of the pathophysiology is needed to improve diagnosis and treatment. NAFLD is a highly heritable disease (20-70%) with prevalence rates that vary across ethnic groups, i.e. individuals of Hispanic ancestry have a higher prevalence than European and African ancestry individuals. One of the first published GWAS was our work from the Genetics of Obesity-associated Liver Disease (GOLD) Consortium identifying five loci associated with computed tomography-measured liver attenuation in European-ancestry populations. Trans ethnic analyses confirmed some associations and also identified ancestry specific alleles suggesting novel disease promoting loci may exist in minority populations. Since known variation explains only 4.8% of the variance in liver attenuation, additional genetic loci that impact predisposition to NAFLD remain to be discovered. The objective of this application is to identify additional rare variants with effects on NAFLD through whole genome sequencing (WGS) in ethnically diverse populations included in NHLBI’s Trans-Omics for Precision Medicine (TOPMed) Consortium (n=23,156). We will replicate effects in GOLD cohorts (n=8,865) lacking WGS by imputing GWAS data to the TOPMed reference panel. Implicated genes from these single rare variant and rare variant burden testing analyses will be functionally tested for effects on hepatic steatosis to confirm causality. Our central hypothesis is that rare variants contribute to variation and risk. These WGS identified variants can help prioritize loci that can be targeted for NAFLD therapy. Our long-term goal is to improve the diagnosis, management, treatment and ultimately prevention of NAFLD by understanding the genomic contributions to pathophysiology. Results from our work will help us to understand the genetic architecture of NAFLD and link these associations to genes that can be targeted for therapeutic intervention.