Variants in PCSK7, PNPLA3 and TM6SF2 are risk factors for the development of cirrhosis in hereditary haemochromatosis

Background: Cirrhosis develops in <10% of individuals homozygous for the C282Y variant in the homeostatic iron regulator (HFE) gene. Carriage of PCSK7:rs236918 is associated with an increased risk of cirrhosis in this population. Aim: To determine if genetic variants significantly associated with the risk of alcohol- and NAFLD-related cirrhosis also modulate the cirrhosis risk in C282Y homozygotes. Methods: Variants in PCSK7, PNPLA3, TM6SF2, MBOAT7 and HSD17B13 were genotyped in 1319 C282Y homozygotes, from six European countries, of whom 171 (13.0%) had cirrhosis. Genotypic and allelic associations with the risk for developing cirrhosis were assessed, adjusting for age and sex. Fixed effects meta-analyses of the adjusted summary data for each country were performed. Post hoc association testing was undertaken in the 131 (76.6%) cases and 299 (26.0%) controls with available liver histology. Results: Significant associations were observed between PCSK7:rs236918 (OR = 1.52 [95% CI 1.06-2.19]; P = 0.022; I2 = 0%); PNPLA3:rs738409 (OR = 1.60 [95% CI 1.22-2.11]; P = 7.37 × 10−4; I2 = 45.5%) and TM6SF2:rs58542926 (OR = 1.94 [95% CI 1.28-2.95]; P = 1.86 × 10−3; I2 = 0%) and the cirrhosis risk in C282Y homozygotes. These findings remained significant in the subpopulation with available liver histology. The population-attributable fractions were 5.6% for PCSK7:rs236918, 13.8% for PNPLA3:rs738409, 6.5% for TM6SF2:rs58542926 and 24.0% for carriage of all three variants combined. Conclusions: The risk of cirrhosis associated with carriage of PCSK7:rs236918 was confirmed in this much larger population of C282Y homozygotes. In addition, PNPLA3:rs738409 and TM6SF2:rs58542926 were established as significant additional risk factors. More detailed genetic testing of C282Y homozygotes would allow risk stratification and help guide future management.