894
C.-M. Tai et al. / Surgery for Obesity and Related Diseases 11 (2015) 888–896
[12] Sookoian S, Pirola CJ. Meta-analysis of the influence of I148 M variant of patatin-like phospholipase domain containing 3 gene (PNPLA3) on the susceptibility and histological severity of nonalcoholic fatty liver disease. Hepatology 2011;53:1883–94. [13] Hotta K, Yoneda M, Hyogo H, et al. Association of the rs738409 polymorphism in PNPLA3 with liver damage and the development of nonalcoholic fatty liver disease. BMC Med Genet 2010;11:172. [14] Wang CW, Lin HY, Shin SJ, et al. The PNPLA3 I148 M polymorphism is associated with insulin resistance and nonalcoholic fatty liver disease in a normoglycaemic population. Liver Int 2011;31:1326–31. [15] Kawaguchi T, Sumida Y, Umemura A, et al. Genetic polymorphisms of the human PNPLA3 gene are strongly ass ociated with severity of non-alcoholic fatty liver disease in Japanese. PLoS One 2012;7:e38322. [16] Clark JM. The epidemiology of nonalcoholic fatty liver disease in adults. J Clin Gastroenterol 2006;40(Suppl 1):S5–10. [17] Romeo S, Sentinelli F, Dash S, et al. Morbid obesity exposes the association between PNPLA3 I148 M (rs738409) and indices of hepatic injury in individuals of European descent. Int J Obes (Lond) 2010;34:190–4. [18] Guichelaar MM, Gawrieh S, Olivier M, et al. Interactions of allelic variance of PNPLA3 with nongenetic factors in predicting nonalcoholic steatohepatitis and nonhepatic complications of severe obesity. Obesity (Silver Spring) 2013;21:1935–41. [19] Lee WJ, Wang W. Bariatric surgery: Asia-Pacific perspective. Obes Surg 2005;15:751–7. [20] Wallace TM, Levy JC, Matthews DR. Use and abuse of HOMA modeling. Diabetes Care 2004;27:1487–95.
[21] Brunt EM, Janney CG, Di Bisceglie AM, Neuschwander-Tetri BA, Bacon BR. Nonalcoholic steatohepatitis: a proposal for grading and staging the histological lesions. Am J Gastroenterol 1999;94: 2467–74. [22] Kleiner DE, Brunt EM. Nonalcoholic fatty liver disease: pathologic patterns and biopsy evaluation in clinical research. Semin Liver Dis. 2012;32:3–13. [23] Kleiner DE, Brunt EM, Van Natta M, et al. Design and validation of a histological scoring system for nonalcoholic fatty liver disease. Hepatology 2005;41:1313–21. [24] Speliotes EK, Butler JL, Palmer CD, Voight BF, Hirschhorn JN. PNPLA3 variants specifically confer increased risk for histologic nonalcoholic fatty liver disease but not metabolic disease. Hepatology 2010;52:904–12. [25] Verrijken A, Beckers S, Francque S, et al. A gene variant of PNPLA3, but not of APOC3, is associated with histological parameters of NAFLD in an obese population. Obesity (Silver Spring) 2013;21:2138–45. [26] Li Y, Xing C, Tian Z, Ku HC. Genetic variant I148 M in PNPLA3 is associated with the ultrasonography-determined steatosis degree in a Chinese population. BMC Med Genet 2012;13:113. [27] Saadeh S, Younossi ZM, Remer EM, et al. The utility of radiological imaging in nonalcoholic fatty liver disease. Gastroenterology 2002;123:745–50. [28] Giudice EM, Grandone A, Cirillo G, et al. The association of PNPLA3 variants with liver enzymes in childhood obesity is driven by the interaction with abdominal fat. PLoS One 2011;6:e27933.
Editorial comment
The PNPLA3 p.Ile148Met Variant and Obesity: brothers-in-arms According to the latest studies [1], we are facing a worldwide obesity epidemic. As the result, fatty liver disease (FLD), the hepatic fellow traveler of obesity [2], is becoming the most prevalent liver disorder [3]. Given improvements in the treatment of viral liver diseases, FLD and its severe form, nonalcoholic steatohepatitis (NASH), might become the leading cause for liver transplantation. In the present study, Tai et al. aim to determine the association between the frequent polymorphism p.Ile148Met of the adiponutrin gene PNPLA3 and the presence of NASH in obese individuals [4]. This variant has emerged in recent years as the major genetic determinant of FLD [5,6]. Analyses encompassing multiple genome-wide association studies and candidate gene association tests in thousands of individuals from different populations demonstrated that carriers of the rare PNPLA3 allele p.148Met are susceptible to develop increased hepatic lipid content [5–7]. Interestingly, this association, first demonstrated in adults, has been extended to pediatric cohorts [8]; indeed children carrying this allele are at-risk of liver injury at early stages of their lives [9]. If an individual with the PNPLA3 risk variant suffers from chronic liver disease [10], chronic viral hepatitis [11], or drinks excessive amounts of alcohol [12] then the risk of developing liver cirrhosis may even double
that of the general population. Hence, this variant may on its own cause severe hepatic steatosis but, when present with additional nongenetic risk factors, its presence substantially increases the risk of severe phenotypes. In the present study, Tai et al. [4] analyzed 181 severely obese patients who underwent bariatric surgery at which time liver biopsies were obtained. Among these patients, 60 and 92 presented with FLD and NASH, respectively. The remaining 29 patients did not present any signs of hepatic steatosis at liver biopsy. The p.148 Met/Met genotype proved to be significantly associated with the development of NASH; moreover, it increased the NASH score and the steatosis grade. Homozygous carriers of this genotype demonstrated increased serum ALT and AST levels. In comparison with other analyzed risk factors, the PNPLA3 genotype was the strongest determinant of NASH in patients with FLD, and it even outperformed the BMI in the multivariate model. On the other hand, the authors did not find any significant association between the risk variant and the severity of liver scarring in the studied cohort. Overall, these results underscore the strong association between the severity of liver steatosis and the PNPLA3 variant in obese patients. Some limitations of the study have to be noted. First of all, as mentioned by the authors in the
PNPLA3 and NASH in Severely Obese Asians / Surgery for Obesity and Related Diseases 11 (2015) 888–896
Fig. 1. Relation between genetic (PNPLA3 p.Ile148Met) and environmental (obesity) risk factors for fatty liver disease (FLD) and clinical phenotypes. Depending on the triggering factor, FLD may result from genetic or environmental risk factors. However, a subgroup of patients might develop more severe fatty liver disease due to the presence of both genetic and environmental determinants of the disease. Such individuals may require more specific clinical workup and precise therapeutic strategies.
discussion section, only a small number of included individuals suffered from advanced liver fibrosis. This fact might have led to the lack of significant association between the PNPLA3 polymorphism and liver fibrosis in this cohort because of a type 2 statistical error. Secondly, given a relatively small number of individuals without FLD, the study also might have not reached the statistical power required to detect the association between the PNPLA3 variant and FLD overall, and not only NASH. Further studies in larger cohorts of obese individuals would be required to delineate the full spectrum of genetic associations. On the other hand, the present study clearly emphasizes that obese individuals who are homozygous carriers of the PNPLA3 risk allele p.148Met are at a substantially increased risk of severe hepatic steatosis. What is the meaning of this study clinically? Although FLD has for a long time been associated with obesity, the PNPLA3 variant constitutes such a strong risk factor for hepatic steatosis that patients carrying the prosteatotic variant are at risk of hepatic steatosis and steatohepatitis even when not overweight. Indeed, we have lately proposed PNPLA3-associated steatohepatitis (PASH) [7] as a novel gene-based liver disease. In particular, homozygous carriers of the PNPLA3 p.Ile148Met genotype are susceptible to fatty liver and NASH, but also liver fibrosis, cirrhosis and its malignant complication, namely hepatocellular carcinoma (HCC), in the absence of additional nongenetic triggers. What happens if in a given individual 2 major risk factors for severe steatosis (i.e., obesity and the PNPLA3 mutation) co-exist? Fig. 1 illustrates the concept of 3 types of FLD, with possible outcomes based on the presence of either obesity, PASH, or both. Of note, in the
895
present study the odds ratio of developing NASH among carriers of the risk variant was 3.7, in other words it was substantially increased. This degree of association implies that obesity and variant PNPLA3 might boost the harmful effect of one another on chronic liver injury. Indeed, previous studies have demonstrated that the presence of obesity could potentiate the harmful effects of the PNPLA3 p.148Met allele – as has been shown for obese children [13] and for patients with chronic hepatitis B [14] or hepatitis C virus infection [15]. Studies like the current one [4] improve our understanding of interaction between environment and genetic background in chronic liver diseases. Importantly, further analyses are required to address the questions arising from the present and previous studies on PNPLA3. Should we offer more effective diets to obese patients who test positive for the PNPLA3 mutation? Can the PNPLA3 allele affect the results of dietary interventions in FLD? How should we follow-up these patients to prevent the development of HCC? We will need to answer these and further questions in the coming years if we want to prevent the epidemic increase of fatty liver and its sequelae. Marcin Krawczyk Frank Lammert Department of Medicine II Saarland University Medical Center Homburg, Germany References [1] Ng M, Fleming T, Robinson M, et al. Global, regional, and national prevalence of overweight and obesity in children and adults during 1980-2013: a systematic analysis for the Global Burden of Disease Study 2013. Lancet 2013;384:766-81. [2] Cusi K. Role of obesity and lipotoxicity in the development of nonalcoholic steatohepatitis: pathophysiology and clinical implications. Gastroenterology 2012;142:711–25.e6. [3] Blachier M, Leleu H, Peck-Radosavljevic M, et al. The burden of liver disease in Europe: a review of available epidemiological data. J Hepatol 2013;58:593–608. [4] Tai CM, Huang CK, Tu HP, et al. PNPLA3 genotype increases susceptibility of nonalcoholic steatohepatitis among obese patients with nonalcoholic fatty liver disease. Surg Obes Relat Dis 2015;11(4):888–94. [5] Anstee QM, Day CP. The genetics of NAFLD. Nat Rev Gastroenterol Hepatol 2013;10:645–55. [6] Sookoian S, Pirola CJ. Meta-analysis of the influence of I148 M variant of patatin-like phospholipase domain containing 3 gene (PNPLA3) on the susceptibility and histological severity of nonalcoholic fatty liver disease. Hepatology 2011;53:1883–94. [7] Krawczyk M, Portincasa P, Lammert F. PNPLA3-associated steatohepatitis: toward a gene-based classification of fatty liver disease. Semin Liver Dis 2013;33:369–79. [8] Valenti L, Al-Serri A, Daly AK, et al. Homozygosity for the patatinlike phospholipase-3/adiponutrin I148 M polymorphism influences liver fibrosis in patients with nonalcoholic fatty liver disease. Hepatology 2010;51:1209–17. [9] Viitasalo A, Pihlajamaki J, Lindi V, et al. Associations of I148 M variant in PNPLA3 gene with plasma ALT levels during 2-year
896
C.-M. Tai et al. / Surgery for Obesity and Related Diseases 11 (2015) 888–896
follow-up in normal weight and overweight children: the PANIC Study. Pediatr Obes. Epub 2014 Jun 11. [10] Krawczyk M, Grünhage F, Zimmer V, Lammert F. Variant adiponutrin (PNPLA3) represents a common fibrosis risk gene: non-invasive elastography-based study in chronic liver disease. J Hepatol 2011;55:299–306. [11] Valenti L, Rumi M, Galmozzi E, et al. Patatin-like phospholipase domain-containing 3 I148 M polymorphism, steatosis, and liver damage in chronic hepatitis C. Hepatology 2011;53:791–9. [12] Tian C, Stokowski RP, Kershenobich D, et al. Variant in PNPLA3 is associated with alcoholic liver disease. Nat Genet 2010;42:21–3.
[13] Giudice EM, Grandone A, Cirillo G, et al. The association of PNPLA3 variants with liver enzymes in childhood obesity is driven by the interaction with abdominal fat. PLoS One 2011;6:e27933. [14] Vigano M, Valenti L, Lampertico P, et al. Patatin-like phospholipase domain-containing 3 I148 M affects liver steatosis in patients with chronic hepatitis B. Hepatology 2013;58:1245–52. [15] Zampino R, Coppola N, Cirillo G, et al. Abdominal fat interacts with PNPLA3 I148 M, but not with the APOC3 variant in the pathogenesis of liver steatosis in chronic hepatitis C. J Viral Hepat 2013;20: 517–23.
C.-M. Tai et al. / Surgery for Obesity and Related Diseases 11 (2015) 888–896
[12] Sookoian S, Pirola CJ. Meta-analysis of the influence of I148 M variant of patatin-like phospholipase domain containing 3 gene (PNPLA3) on the susceptibility and histological severity of nonalcoholic fatty liver disease. Hepatology 2011;53:1883–94. [13] Hotta K, Yoneda M, Hyogo H, et al. Association of the rs738409 polymorphism in PNPLA3 with liver damage and the development of nonalcoholic fatty liver disease. BMC Med Genet 2010;11:172. [14] Wang CW, Lin HY, Shin SJ, et al. The PNPLA3 I148 M polymorphism is associated with insulin resistance and nonalcoholic fatty liver disease in a normoglycaemic population. Liver Int 2011;31:1326–31. [15] Kawaguchi T, Sumida Y, Umemura A, et al. Genetic polymorphisms of the human PNPLA3 gene are strongly ass ociated with severity of non-alcoholic fatty liver disease in Japanese. PLoS One 2012;7:e38322. [16] Clark JM. The epidemiology of nonalcoholic fatty liver disease in adults. J Clin Gastroenterol 2006;40(Suppl 1):S5–10. [17] Romeo S, Sentinelli F, Dash S, et al. Morbid obesity exposes the association between PNPLA3 I148 M (rs738409) and indices of hepatic injury in individuals of European descent. Int J Obes (Lond) 2010;34:190–4. [18] Guichelaar MM, Gawrieh S, Olivier M, et al. Interactions of allelic variance of PNPLA3 with nongenetic factors in predicting nonalcoholic steatohepatitis and nonhepatic complications of severe obesity. Obesity (Silver Spring) 2013;21:1935–41. [19] Lee WJ, Wang W. Bariatric surgery: Asia-Pacific perspective. Obes Surg 2005;15:751–7. [20] Wallace TM, Levy JC, Matthews DR. Use and abuse of HOMA modeling. Diabetes Care 2004;27:1487–95.
[21] Brunt EM, Janney CG, Di Bisceglie AM, Neuschwander-Tetri BA, Bacon BR. Nonalcoholic steatohepatitis: a proposal for grading and staging the histological lesions. Am J Gastroenterol 1999;94: 2467–74. [22] Kleiner DE, Brunt EM. Nonalcoholic fatty liver disease: pathologic patterns and biopsy evaluation in clinical research. Semin Liver Dis. 2012;32:3–13. [23] Kleiner DE, Brunt EM, Van Natta M, et al. Design and validation of a histological scoring system for nonalcoholic fatty liver disease. Hepatology 2005;41:1313–21. [24] Speliotes EK, Butler JL, Palmer CD, Voight BF, Hirschhorn JN. PNPLA3 variants specifically confer increased risk for histologic nonalcoholic fatty liver disease but not metabolic disease. Hepatology 2010;52:904–12. [25] Verrijken A, Beckers S, Francque S, et al. A gene variant of PNPLA3, but not of APOC3, is associated with histological parameters of NAFLD in an obese population. Obesity (Silver Spring) 2013;21:2138–45. [26] Li Y, Xing C, Tian Z, Ku HC. Genetic variant I148 M in PNPLA3 is associated with the ultrasonography-determined steatosis degree in a Chinese population. BMC Med Genet 2012;13:113. [27] Saadeh S, Younossi ZM, Remer EM, et al. The utility of radiological imaging in nonalcoholic fatty liver disease. Gastroenterology 2002;123:745–50. [28] Giudice EM, Grandone A, Cirillo G, et al. The association of PNPLA3 variants with liver enzymes in childhood obesity is driven by the interaction with abdominal fat. PLoS One 2011;6:e27933.
Editorial comment
The PNPLA3 p.Ile148Met Variant and Obesity: brothers-in-arms According to the latest studies [1], we are facing a worldwide obesity epidemic. As the result, fatty liver disease (FLD), the hepatic fellow traveler of obesity [2], is becoming the most prevalent liver disorder [3]. Given improvements in the treatment of viral liver diseases, FLD and its severe form, nonalcoholic steatohepatitis (NASH), might become the leading cause for liver transplantation. In the present study, Tai et al. aim to determine the association between the frequent polymorphism p.Ile148Met of the adiponutrin gene PNPLA3 and the presence of NASH in obese individuals [4]. This variant has emerged in recent years as the major genetic determinant of FLD [5,6]. Analyses encompassing multiple genome-wide association studies and candidate gene association tests in thousands of individuals from different populations demonstrated that carriers of the rare PNPLA3 allele p.148Met are susceptible to develop increased hepatic lipid content [5–7]. Interestingly, this association, first demonstrated in adults, has been extended to pediatric cohorts [8]; indeed children carrying this allele are at-risk of liver injury at early stages of their lives [9]. If an individual with the PNPLA3 risk variant suffers from chronic liver disease [10], chronic viral hepatitis [11], or drinks excessive amounts of alcohol [12] then the risk of developing liver cirrhosis may even double
that of the general population. Hence, this variant may on its own cause severe hepatic steatosis but, when present with additional nongenetic risk factors, its presence substantially increases the risk of severe phenotypes. In the present study, Tai et al. [4] analyzed 181 severely obese patients who underwent bariatric surgery at which time liver biopsies were obtained. Among these patients, 60 and 92 presented with FLD and NASH, respectively. The remaining 29 patients did not present any signs of hepatic steatosis at liver biopsy. The p.148 Met/Met genotype proved to be significantly associated with the development of NASH; moreover, it increased the NASH score and the steatosis grade. Homozygous carriers of this genotype demonstrated increased serum ALT and AST levels. In comparison with other analyzed risk factors, the PNPLA3 genotype was the strongest determinant of NASH in patients with FLD, and it even outperformed the BMI in the multivariate model. On the other hand, the authors did not find any significant association between the risk variant and the severity of liver scarring in the studied cohort. Overall, these results underscore the strong association between the severity of liver steatosis and the PNPLA3 variant in obese patients. Some limitations of the study have to be noted. First of all, as mentioned by the authors in the
PNPLA3 and NASH in Severely Obese Asians / Surgery for Obesity and Related Diseases 11 (2015) 888–896
Fig. 1. Relation between genetic (PNPLA3 p.Ile148Met) and environmental (obesity) risk factors for fatty liver disease (FLD) and clinical phenotypes. Depending on the triggering factor, FLD may result from genetic or environmental risk factors. However, a subgroup of patients might develop more severe fatty liver disease due to the presence of both genetic and environmental determinants of the disease. Such individuals may require more specific clinical workup and precise therapeutic strategies.
discussion section, only a small number of included individuals suffered from advanced liver fibrosis. This fact might have led to the lack of significant association between the PNPLA3 polymorphism and liver fibrosis in this cohort because of a type 2 statistical error. Secondly, given a relatively small number of individuals without FLD, the study also might have not reached the statistical power required to detect the association between the PNPLA3 variant and FLD overall, and not only NASH. Further studies in larger cohorts of obese individuals would be required to delineate the full spectrum of genetic associations. On the other hand, the present study clearly emphasizes that obese individuals who are homozygous carriers of the PNPLA3 risk allele p.148Met are at a substantially increased risk of severe hepatic steatosis. What is the meaning of this study clinically? Although FLD has for a long time been associated with obesity, the PNPLA3 variant constitutes such a strong risk factor for hepatic steatosis that patients carrying the prosteatotic variant are at risk of hepatic steatosis and steatohepatitis even when not overweight. Indeed, we have lately proposed PNPLA3-associated steatohepatitis (PASH) [7] as a novel gene-based liver disease. In particular, homozygous carriers of the PNPLA3 p.Ile148Met genotype are susceptible to fatty liver and NASH, but also liver fibrosis, cirrhosis and its malignant complication, namely hepatocellular carcinoma (HCC), in the absence of additional nongenetic triggers. What happens if in a given individual 2 major risk factors for severe steatosis (i.e., obesity and the PNPLA3 mutation) co-exist? Fig. 1 illustrates the concept of 3 types of FLD, with possible outcomes based on the presence of either obesity, PASH, or both. Of note, in the
895
present study the odds ratio of developing NASH among carriers of the risk variant was 3.7, in other words it was substantially increased. This degree of association implies that obesity and variant PNPLA3 might boost the harmful effect of one another on chronic liver injury. Indeed, previous studies have demonstrated that the presence of obesity could potentiate the harmful effects of the PNPLA3 p.148Met allele – as has been shown for obese children [13] and for patients with chronic hepatitis B [14] or hepatitis C virus infection [15]. Studies like the current one [4] improve our understanding of interaction between environment and genetic background in chronic liver diseases. Importantly, further analyses are required to address the questions arising from the present and previous studies on PNPLA3. Should we offer more effective diets to obese patients who test positive for the PNPLA3 mutation? Can the PNPLA3 allele affect the results of dietary interventions in FLD? How should we follow-up these patients to prevent the development of HCC? We will need to answer these and further questions in the coming years if we want to prevent the epidemic increase of fatty liver and its sequelae. Marcin Krawczyk Frank Lammert Department of Medicine II Saarland University Medical Center Homburg, Germany References [1] Ng M, Fleming T, Robinson M, et al. Global, regional, and national prevalence of overweight and obesity in children and adults during 1980-2013: a systematic analysis for the Global Burden of Disease Study 2013. Lancet 2013;384:766-81. [2] Cusi K. Role of obesity and lipotoxicity in the development of nonalcoholic steatohepatitis: pathophysiology and clinical implications. Gastroenterology 2012;142:711–25.e6. [3] Blachier M, Leleu H, Peck-Radosavljevic M, et al. The burden of liver disease in Europe: a review of available epidemiological data. J Hepatol 2013;58:593–608. [4] Tai CM, Huang CK, Tu HP, et al. PNPLA3 genotype increases susceptibility of nonalcoholic steatohepatitis among obese patients with nonalcoholic fatty liver disease. Surg Obes Relat Dis 2015;11(4):888–94. [5] Anstee QM, Day CP. The genetics of NAFLD. Nat Rev Gastroenterol Hepatol 2013;10:645–55. [6] Sookoian S, Pirola CJ. Meta-analysis of the influence of I148 M variant of patatin-like phospholipase domain containing 3 gene (PNPLA3) on the susceptibility and histological severity of nonalcoholic fatty liver disease. Hepatology 2011;53:1883–94. [7] Krawczyk M, Portincasa P, Lammert F. PNPLA3-associated steatohepatitis: toward a gene-based classification of fatty liver disease. Semin Liver Dis 2013;33:369–79. [8] Valenti L, Al-Serri A, Daly AK, et al. Homozygosity for the patatinlike phospholipase-3/adiponutrin I148 M polymorphism influences liver fibrosis in patients with nonalcoholic fatty liver disease. Hepatology 2010;51:1209–17. [9] Viitasalo A, Pihlajamaki J, Lindi V, et al. Associations of I148 M variant in PNPLA3 gene with plasma ALT levels during 2-year
896
C.-M. Tai et al. / Surgery for Obesity and Related Diseases 11 (2015) 888–896
follow-up in normal weight and overweight children: the PANIC Study. Pediatr Obes. Epub 2014 Jun 11. [10] Krawczyk M, Grünhage F, Zimmer V, Lammert F. Variant adiponutrin (PNPLA3) represents a common fibrosis risk gene: non-invasive elastography-based study in chronic liver disease. J Hepatol 2011;55:299–306. [11] Valenti L, Rumi M, Galmozzi E, et al. Patatin-like phospholipase domain-containing 3 I148 M polymorphism, steatosis, and liver damage in chronic hepatitis C. Hepatology 2011;53:791–9. [12] Tian C, Stokowski RP, Kershenobich D, et al. Variant in PNPLA3 is associated with alcoholic liver disease. Nat Genet 2010;42:21–3.
[13] Giudice EM, Grandone A, Cirillo G, et al. The association of PNPLA3 variants with liver enzymes in childhood obesity is driven by the interaction with abdominal fat. PLoS One 2011;6:e27933. [14] Vigano M, Valenti L, Lampertico P, et al. Patatin-like phospholipase domain-containing 3 I148 M affects liver steatosis in patients with chronic hepatitis B. Hepatology 2013;58:1245–52. [15] Zampino R, Coppola N, Cirillo G, et al. Abdominal fat interacts with PNPLA3 I148 M, but not with the APOC3 variant in the pathogenesis of liver steatosis in chronic hepatitis C. J Viral Hepat 2013;20: 517–23.
