title: The rs2294918 E434K variant modulates patatin-like phospholipase domain-containing 3 expression and liver damage.
abstract: The patatin-like phosholipase domain-containing 3 (PNPLA3) rs738409 polymorphism (I148M) is a major determinant of hepatic fat and predisposes to the full spectrum of liver damage in nonalcoholic fatty liver disease (NAFLD). The aim of this study was to evaluate whether additional PNPLA3 coding variants contribute to NAFLD susceptibility, first in individuals with contrasting phenotypes (with early-onset NAFLD vs. very low aminotransferases) and then in a large validation cohort. Rare PNPLA3 variants were not detected by sequencing coding regions and intron-exon boundaries either in 142 patients with early-onset NAFLD nor in 100 healthy individuals with alanine aminotransferase <22/20 IU/mL. Besides rs738409 I148M, the rs2294918 G>A polymorphism (E434K sequence variant) was over-represented in NAFLD (adjusted P = 0.01). In 1,447 subjects with and without NAFLD, the 148M-434E (P < 0.0001), but not the 148M-434K, haplotype (P > 0.9), was associated with histological NAFLD and steatohepatitis. Both the I148M (P = 0.0002) and E434K variants (P = 0.044) were associated with serum ALT levels, by interacting with each other, in that the 434K hampered the association with liver damage of the 148M allele (P = 0.006). The E434K variant did not affect PNPLA3 enzymatic activity, but carriers of the rs2294918 A allele (434K) displayed lower hepatic PNPLA3 messenger RNA and protein levels (P < 0.05).
  
  
  CONCLUSIONS
  Rare loss-of-function PNPLA3 variants were not detected in early-onset NAFLD. However, PNPLA3 rs2294918 E434K decreased PNPLA3 expression, lessening the effect of the I148M variant on the predisposition to steatosis and liver damage. This suggests that the PNPLA3 I148M variant has a codominant negative effect on triglycerides mobilization from lipid droplets, mediated by inhibition of other lipases.
authors.affiliation: Department of Pathophysiology and Transplantation, Università degli Studi di Milano, Fondazione IRCCS Ca' Granda Ospedale Policlinico, Milano, Italy.
authors.forename: Benedetta
authors.initials: B
authors.lastname: Donati
authors.affiliation: Department of Pathophysiology and Transplantation, Università degli Studi di Milano, Fondazione IRCCS Ca' Granda Ospedale Policlinico, Milano, Italy.|Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory, Department of Molecular and Clinical Medicine, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Benedetta Maria
authors.initials: BM
authors.lastname: Motta
authors.affiliation: Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory, Department of Molecular and Clinical Medicine, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Piero
authors.initials: P
authors.lastname: Pingitore
authors.affiliation: Department of Pathophysiology and Transplantation, Università degli Studi di Milano, Fondazione IRCCS Ca' Granda Ospedale Policlinico, Milano, Italy.
authors.forename: Marica
authors.initials: M
authors.lastname: Meroni
authors.affiliation: Department of Pathophysiology and Transplantation, Università degli Studi di Milano, Fondazione IRCCS Ca' Granda Ospedale Policlinico, Milano, Italy.|Istituto Nazionale Genetica Molecolare (INGM), "Romeo ed Enrica Invernizzi", Bioinformatic Group, Milano, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Pietrelli
authors.affiliation: Hepato-Metabolic Unit, Ospedale Bambin Gesù, Roma, Italy.
authors.forename: Anna
authors.initials: A
authors.lastname: Alisi
authors.affiliation: Department of Gastroenterology, Università di Palermo, Palermo, Italy.
authors.forename: Salvatore
authors.initials: S
authors.lastname: Petta
authors.affiliation: UT Southwestern Medical Center, Dallas, TX.
authors.forename: Chao
authors.initials: C
authors.lastname: Xing
authors.affiliation: Department of Pathophysiology and Transplantation, Università degli Studi di Milano, Fondazione IRCCS Ca' Granda Ospedale Policlinico, Milano, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Dongiovanni
authors.affiliation: Department of Pathophysiology and Transplantation, Università degli Studi di Milano, Fondazione IRCCS Ca' Granda Ospedale Policlinico, Milano, Italy.
authors.forename: Benedetta
authors.initials: B
authors.lastname: del Menico
authors.affiliation: Department of Pathophysiology and Transplantation, Università degli Studi di Milano, Fondazione IRCCS Ca' Granda Ospedale Policlinico, Milano, Italy.
authors.forename: Raffaela
authors.initials: R
authors.lastname: Rametta
authors.affiliation: Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory, Department of Molecular and Clinical Medicine, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Rosellina Margherita
authors.initials: RM
authors.lastname: Mancina
authors.affiliation: Department of Pathophysiology and Transplantation, Università degli Studi di Milano, Fondazione IRCCS Ca' Granda Ospedale Policlinico, Milano, Italy.
authors.forename: Sara
authors.initials: S
authors.lastname: Badiali
authors.affiliation: Department of Pathophysiology and Transplantation, Università degli Studi di Milano, Fondazione IRCCS Ca' Granda Ospedale Policlinico, Milano, Italy.
authors.forename: Anna Ludovica
authors.initials: AL
authors.lastname: Fracanzani
authors.affiliation: Department of Gastroenterology, Università di Palermo, Palermo, Italy.
authors.forename: Antonio
authors.initials: A
authors.lastname: Craxì
authors.affiliation: Department of Pathophysiology and Transplantation, Università degli Studi di Milano, Fondazione IRCCS Ca' Granda Ospedale Policlinico, Milano, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Fargion
authors.affiliation: Hepato-Metabolic Unit, Ospedale Bambin Gesù, Roma, Italy.
authors.forename: Valerio
authors.initials: V
authors.lastname: Nobili
authors.affiliation: Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory, Department of Molecular and Clinical Medicine, University of Gothenburg, Gothenburg, Sweden.|Clinical Nutrition Unit, Department of Medical and Surgical Sciences, University Magna Graecia, Catanzaro, Italy.|Department of Cardiology, Sahlgrenska University Hospital, Gothenburg, Sweden.
authors.forename: Stefano
authors.initials: S
authors.lastname: Romeo
authors.affiliation: Department of Pathophysiology and Transplantation, Università degli Studi di Milano, Fondazione IRCCS Ca' Granda Ospedale Policlinico, Milano, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Valenti
mesh_terms: D000293:Adolescent; D000328:Adult; D000410:Alanine Transaminase / Q000097:blood; D016022:Case-Control Studies; D002648:Child; D005260:Female; D020022:Genetic Predisposition to Disease; D006239:Haplotypes; D006801:Humans; D008049:Lipase / Q000235:genetics*; D050356:Lipid Metabolism / Q000235:genetics; D008099:Liver / Q000473:pathology; D008297:Male; D008565:Membrane Proteins / Q000235:genetics*; D008875:Middle Aged; D065626:Non-alcoholic Fatty Liver Disease / Q000235:genetics* / Q000473:pathology; D020641:Polymorphism, Single Nucleotide; D000217:Acyltransferases; D054512:Phospholipases A2, Calcium-Independent
chemical_list: D000410:Alanine Transaminase; D008049:Lipase; D008565:Membrane Proteins; C533682:PNPLA3 protein, human; D000217:Acyltransferases; D054512:Phospholipases A2, Calcium-Independent