GENOME-WIDE ASSOCIATION STUDY OF NON-INVASIVE ASSESSMENT OF LIVER FIBROSIS IN MASLD: EVIDENCE FROM AN ITALIAN POPULATION

Metabolic Associated Steatotic Liver Disease (MASLD) is the most prevalent cause of chronic liver disease worldwide and a significant risk factor for cirrhosis and hepatocellular carcinoma (HCC). Despite its pathogenesis being determined by both environmental and genetic determinants, the genetic component of fibrosis progression is still only partially known, particularly in the Italian population. This Ph.D. project aimed to detect genetic variants implicated in advanced liver fibrosis in MASLD by performing a cross-sectional genome-wide association study (GWAS) using non-invasive fibrosis markers in a large biobank environment. The analysis was performed in the Milan Biobank, a multicenter cohort of 7,025 individuals encompassing healthy blood donors, metabolic dysfunction patients, and liver disease subjects across the MASLD spectrum. Clinical phenotyping was based on validated non-invasive indices: the Fibrosis-4 index (FIB-4) was used as the primary outcome, whereas the Fibrotic NASH Index (FNI) and serum liver enzymes, namely alanine transaminase (ALT), aspartate transaminase (AST), gamma-glutamyl transferase (GGT), were investigated as secondary phenotypes. The GWAS confirmed the strong effects of PNPLA3 and TM6SF2 on MASLD progression and fibrosis. Novel associations were identified at the MRC1 and MAGEE2 loci for FIB-4, and at IFI27 and DIAPH2 for FNI, implicating immune regulation and cytoskeletal remodeling as additional pathways driving fibrosis susceptibility. Replication analyses in the UK Biobank (UKBB, N>400,000) validated associations at MRC1, reinforcing the reliability and generalizability of these findings. Functional follow-up analyses, including transcriptomics and phenome-wide association study (PheWAS), highlighted downregulation of MRC1 in patients with advanced fibrosis and hepatocellular ballooning, further linking this locus to inflammatory mechanisms of liver injury. Along with locus discovery, polygenic risk scores (PRSs) were derived from GWAS summary statistics and contrasted with pre-existing PRSs. These investigations revealed that PRSs including fibrosis-associated loci enhanced fibrosis, cirrhosis, and HCC prediction, with performance differing between traits. Notably, partitioned PRSs (pPRSs) discriminated against liver-specific vs. systemic MASLD pathways, providing insight into disease heterogeneity and the basis for divergent progression patterns in patients. In summary, this project represents the first comprehensive GWAS of non-invasively assessed liver fibrosis in an Italian population. It identified both known and novel susceptibility loci, replicated significant findings in independent cohorts, and integrated functional genomics to support biological interpretation. Clinically, the findings underscore the potential of combining genetic information with non-invasive biomarkers to refine risk stratification, enable earlier detection of high-risk individuals, and inform the development of precision medicine strategies for MASLD. These findings substantially advance the understanding of MASLD genetics and set the stage for targeted therapeutic approaches.