Synergistic Associations of PNPLA3 I148M Variant, Alcohol Intake, and Obesity With Risk of Cirrhosis, Hepatocellular Carcinoma, and Mortality

IMPORTANCE Alcohol drinking and obesity are associated with an increased risk of cirrhosis and hepatocellular carcinoma (HCC), but the risk is not uniform among people with these risk factors. Genetic variants, such as I148M in the patatin-like phospholipase domain-containing protein 3 (PNPLA3) gene, may play an important role in modulating cirrhosis and HCC risk. OBJECTIVE To investigate the joint associations of the PNPLA3I148M variant, alcohol intake, and obesity with the risk of cirrhosis, HCC, and liver disease-related mortality. DESIGN, SETTING, AND PARTICIPANTS This prospective cohort study analyzed 414 209 participants enrolled in the UK Biobank study from March 2006 to December 2010. Participants had no previous diagnosis of cirrhosis and HCC and were followed up through March 2021. EXPOSURES Self-reported alcohol intake (nonexcessive vs excessive), obesity (body mass index >= 30 [calculated as weight in kilograms divided by height in meters squared]), and PNPLA3 I148M variant status (noncarrier, heterozygous carrier, or homozygous carrier) from initial assessment. MAIN OUTCOMES AND MEASURES The primary outcomes were incident cirrhosis and HCC cases and liver disease-related death ascertained from inpatient hospitalization records and death registry. The risks were calculated by Cox proportional hazards regression models. RESULTS A total of 414209 participants (mean [SD] age, 56.3 [8.09] years; 218 567 women [52.8%]; 389 452 White race and ethnicity [94.0%]) were included. Of these participants, 2398 participants (0.6%) developed cirrhosis (5.07 [95% CI, 4.87-5.28] cases per 100 person-years), 323 (0.1%) developed HCC (0.68 [95% CI, 0.61.0.76] cases per 100 person-years), and 878 (0.2%) died from a liver disease-related cause (1.76 [95% CI, 1.64-1.88] cases per 100 person-years) during a median follow-up of 10.9 years. Synergistic interactions between the PNPLA3I148M variant, obesity, and alcohol intake were associated with the risk of cirrhosis, HCC, and liver disease-related mortality. The risk of cirrhosis increased supramultiplicatively (adjusted hazard ratio [a HR], 17.52; 95% CI, 12.84-23.90) in individuals with obesity, with excessive drinking, and who were homozygous carriers compared with those with no obesity, with nonexcessive drinking, and who were noncarriers. Supramultiplicative associations between the 3 factors and risks of HCC were found in individuals with 3 risk factors (aHR, 30.13; 95% CI, 16.51-54.98) and liver disease-related mortality (aHR, 21.82; 95% CI, 13.78-34.56). The PNPLA3 I148M variant status significantly differentiated the risk of cirrhosis, HCC, and liver disease-related mortality in persons with excessive drinking and obesity. CONCLUSIONS AND RELEVANCE This study found synergistic associations of the PNPLA3 I148M variant, excessive alcohol intake, and obesity with increased risk of cirrhosis, HCC, and liver disease related death in the general population. The PNPLA3 I148M variant status may help refine the risk stratification for liver disease in persons with excessive drinking and obesity who may need early preventive measures.