Abstract
Background: Non-alcoholic fatty liver disease (NAFLD) is the most prevalent form of liver disease. Observational studies documented associations of NAFLD with several chronic and infectious diseases but whether these associations underlie causal effects is unknown. The molecular mechanisms and genetic architecture of NAFLD are poorly understood. Our objectives were to identify genetic loci associated with NAFLD and determine whether the presence of NAFLD was causally associated with human diseases. Methods: We created a NAFLD genetic instrument through the identification of independent single-nucleotide polymorphisms (SNPs) associated with NAFLD in a meta-analysis of genome-wide association study (GWAS) (6715 cases and 682,748 controls). Using inverse-variance weighted Mendelian Randomization (MR), we investigated the impact of NAFLD on human disease-related phenotypes in the UK Biobank and FinnGen cohorts as well as in the COVID-19 host genetics initiative. Results: We first performed a GWAS meta-analysis of four cohorts and found variants significantly associated with NAFLD (p<5.0E-8) at six genetic loci (MTARC1, GCKR, TRIB1, LMO3, SUGP1 [TM6SF2] and PNPLA3). Using a risk factor informed Bayesian approach (bGWAS), we identify variants at three additional loci (LPL, FTO, and APOE). To determine if the association between NAFLD and human diseases shows evidence of causality, we performed MR across the human disease-related phenome (>800 diseases) using a genetic instrument for NAFLD. Results of these analyses suggest that NAFLD was not causally associated with diseases outside the spectrum of liver diseases. We also found no causal association between genetically predicted NAFLD and COVID-19-related outcomes. Conclusions: This study identified several new genetic loci associated with NAFLD. NAFLD was not causally associated with diseases outside those of the spectrum of liver diseases. This finding suggests that the resolution of NAFLD might not prevent other diseases previously associated with NAFLD.