The rs2294918 K434E PNPLA3 Polymorphism is associated with Nonalcoholic Fatty Liver and Steatohepatitis
Luca Valenti1,2, Stefano Romeo3,4, Benedetta M. Motta1,3, Benedetta Del Menico1, Raffaela Rametta1, Giula Buonaiuto1, Anna Alisi5, Anna Ludovica Fracanzani1,2, Enrico Mozzi1,6, Benedetta Donati1, Maria Antonella Burza3, Paolo Dongiovanni2, Valerio Nobili5, Silvia Fargion1,2
1Pathophysiology and Transplanation, Universitá degli Studi di Milano, Milano, Italy; 2Internal Medicine, Fondazione IRCCS Cá Granda Ospedale Policlinico, Milano, Italy; 3Sahlgrenska Center for Cardiovascular ond Metobolic Research/Wallenberg Laboratory, Department of Molecular and Clinical Medicine, University of Gothenburg, Gothenburg, Sweden; 4Clinical Nutrition Unit, Department of Medical and Surgical Sciences, University Magna Graecia, Catanzaro, Italy; 5Hepato-metabolic unit, Ospedale Bambin Gesù, Roma, Italy; 6Surgery, Fondazione IRCCS Cá Granda Ospedale Policlinico, Milano, Italy
Background & aims: The Patatin-like phosholipase domain-containing 3 (PNPLA3) rs738409 polymorphism (I148M) is the major genetic determinant of hepatic fat and predisposes to the full spectrum of liver damage in nonalcoholic fatty liver disease (NAFLD). Aim of this study was to evaluate whether NAFLD is associated with additional PNPLA3 variants. As we detected an association between the rs2294918 polymorphism encoding for the K434E and pediatric NAFLD, which was independent of I148M, we went on to validate these findings in adult patients and to investigate the mechanism by evaluating the association with gene expression. Patients and methods: We considered 142 pediatric and 265 adult patients with histological NAFLD, and 225 healthy controls without NAFLD. Liver damage was assessed by NAFLD activity score, PNPLA3 coding sequence by sequencing, the rs738409 and rs2294918 polymorphisms by Taqman assays, and PNPLA3 expression quantified by qRT-PCR in needle biopsy samples of 60 severely obese patients. Genetic association was tested by Haploview v4.2. Results: Nor novel neither already described rare coding variants of PNPLA3 were detected in pediatric patients and controls. Besides I148M, we identified another variant, rs2294918 A>G (K434E), which was associated with NAFLD (p=9x10-4). The 148I was negatively associated with pediatric NAFLD only in combination with the 434K allele, whereas the 148M was positively associated with NAFLD only in combination with the 434E allele. In pediatric 148I/I patients, the 434E allele at risk of NAFLD was associated with increased ALT (p=0.05). In adult patients, despite being observed at a comparable frequency, only the 148I-434K, but not the 148I-434E, diplotype was negatively associated with NASH, whereas the 148M allele was positively associated with NAFLD only in combination with the 434E allele. At multivariate logistic regression analysis, the K434E variant was associated with NASH independently of I148M status (OR 2.78, 95% c. i. 1.20-6.56). The K434E varaiant was not predicted to alter PNPLA3 function by bioinformatic algorithms, but the 434E at risk allele was associated with higher hepatic PNPLA3 expression (p=0.01). Conclusions: the K434E PNPLA3 variant is associated with predisposition to severe NAFLD in combination with the I148M. Further studies are necessary to clarify the mechanisms, and to assess the effect on other liver-related outcomes.
The following people have nothing to disclose: Luca Valenti, Stefano Romeo, Benedetta M. Motta, Benedetta Del Menico, Raffaela Rametta, Giula Buonaiuto, Anna Alisi, Anna Ludovica Fracanzani, Enrico Mozzi, Benedetta Donati, Maria Antonella Burza, Paola Dongiovanni, Valerio Nobili, Silvia Fargion