Combined effects of the PNPLA3 rs738409, TM6SF2 rs58542926, and MBOAT7 rs641738 variants on NAFLD severity: a multicenter biopsy-based study

Abstract

The PNPLA3 p.I148M, TM6SF2 p.E167K, and MBOAT7 rs641738 variants represent genetic risk factors for nonalcoholic fatty liver disease (NAFLD). Here we investigate if these polymorphisms modulate both steatosis and fibrosis in patients with NAFLD. We recruited 515 patients with NAFLD (age 16-88 years, 280 female patients). Liver biopsies were performed in 320 patients. PCR-based assays were used to genotype the PNPLA3, TM6SF2, and MBOAT7 variants. Carriers of the PNPLA3 and TM6SF2 risk alleles showed increased serum aspartate aminotransferase and alanine transaminase activities (P < 0.05). The PNPLA3 genotype was associated with steatosis grades S2-S3 (P < 0.001) and fibrosis stages F2-F4 (P < 0.001). The TM6SF2 genotype was associated with steatosis (P = 0.003) but not with fibrosis (P > 0.05). The MBOAT7 variant was solely associated with increased fibrosis (P = 0.046). In the multivariate model, variants PNPLA3 (P = 0.004) and TM6SF2 (P = 0.038) were associated with steatosis. Fibrosis stages were affected by the PNPLA3 (P = 0.042) and MBOAT7 (P = 0.021) but not by the TM6SF2 polymorphism (P > 0.05). The PNPLA3, TM6SF2, and MBOAT7 variants are associated with increased liver injury. The TM6SF2 variant seems to modulate predominantly hepatic fat accumulation, whereas the MBOAT7 polymorphism is linked to fibrosis. The PNPLA3 polymorphism confers risk of both increased steatosis and fibrosis.

Keywords: adiponutrin; fatty liver; fibrosis; steatosis.

Fig. 1.

Relation between steatosis grade at liver biopsy and metabolic traits. Increased steatosis was associated with higher serum glucose (A) and triglyceride (B) levels, but it did not affect total cholesterol (C).

Fig. 2.

Box-and-whisker plots illustrating liver function tests in carriers of distinct PNPLA3, TM6SF2, and MBOAT7 variants. Carriers of either PNPLA3 or TM6SF2 risk alleles present with increased AST and ALT activities (A and B for PNPLA3; D and E for TM6SF2). We did not detect any major effects of these variants on the GGT activities (C and F). The MBOAT7 polymorphism did not affect liver function tests. All tests were performed using ANOVA with post hoc tests or with Mann-Whitney U as appropriate. *P < 0.05 in post hoc tests.

Fig. 3.

Combined analysis of the PNPLA3 p.I148M, TM6SF2 p.E167K, and MBOAT7 rs641738 risk alleles on liver function tests. The graphs demonstrate median AST (A), ALT (B), and GGT (C) by the number of risk alleles in either of the tested genes. Analyses were performed using trend test. The following frequencies of carriers of risk alleles were detected: zero risk alleles, n = 56; one risk allele, n = 142; two risk alleles, n = 170; three risk alleles, n = 117; four risk alleles, n = 27; five risk alleles, n = 3.