The common adiponutrin variant p.I148M does not confer gallstone risk but affects fasting glucose and triglyceride levels
Recently the common adiponutrin (PNPLA3) polymorphism p.I148M has been identified as a genetic determinant of severe forms of non-alcoholic fatty liver disease and alcoholic liver disease. Additionally, insulin resistance - linked to the development of non-alcoholic steatohepatitis - increases the risk of developing gallstones. Here we assessed whether the PNPLA3 p.I148M (c.444 C>G) polymorphism affects glucose and lipid levels and increases gallstone risk. We analysed 229 individuals with gallstones from 108 families (age 24-80 years, BMI 17-55 kg/m2) and 258 gallstone-free controls (age 20-70 years, BMI 14-43 kg/m2). Fasting glucose, triglyceride and cholesterol serum levels were determined. The p.I148M polymorphism was genotyped using a PCR-based assay with 5'-nuclease and fluorescence detection. Case-control association tests and nonparametric linkage (NPL) analysis in sib-pairs were performed. Individuals carrying the [GG] genotype had significantly (P<0.0001) higher median fasting glucose levels as compared to [GC] and [CC] carriers. After adjustment for multiple testing, we detected a trend for an association between triglyceride levels and variant adiponutrin in gallstone patients (P=0.032), and gallstone cases carrying the genotype [CC] presented with significantly higher triglyceride levels than the corresponding controls (P<0.003). No significant effects on cholesterol metabolism were detected. Neither genotype distributions nor NPL scores provided evidence for association or linkage between the PNPLA3 variant and gallstones. In conclusion, homozygous carriers of the PNPLA3 risk allele display higher fasting glucose. Although this adiponutrin variant may affect triglyceride homeostasis, it does not increase the risk of cholelithiasis.