Original Article FTO Genotype, Physical Activity, and Coronary Heart Disease Risk in Swedish Men and Women Jaana Gustavsson, MSc; Kirsten Mehlig, PhD; Karin Leander, PhD; Lauren Lissner, MPH, PhD; Lena Björck, PhD; Annika Rosengren, MD, PhD; Fredrik Nyberg, MD, PhD Background—Variants in the fat mass– and obesity-associated gene (FTO) predisposing to obesity and diabetes mellitus have also been associated with cardiovascular disease. Physical activity has been suggested to attenuate the FTO effect on obesity, but it is unknown whether this is also true for cardiovascular disease. Therefore, we explored whether physical activity modifies the FTO association with coronary heart disease (CHD). Methods and Results—FTO rs9939609 (T>A) polymorphism was genotyped in 2 Swedish population–based case–control studies with 1743 CHD cases and 4402 population controls (25–74 years of age; 41% women). Leisure time physical activity was assessed by questionnaires, and 3 levels were defined: low, medium, and high. Overall, carriers of the FTO A allele had an increased risk of CHD (odds ratio, 1.20; 95% confidence interval, 1.06–1.37) adjusted for age, sex, study, and body mass index. Although A-allele carriers with low physical activity had the highest CHD risk (odds ratio, 3.30; 95% confidence interval, 2.44–4.46) compared with those with TT genotype and high activity, the effects of FTO genotype and physical activity on CHD risk were approximately additive, indicating the absence of additive interaction. The stratum-specific relative risks of CHD from the A allele in subjects with low, medium, and high physical activity were odds ratio 1.11 (95% confidence interval, 0.77–1.60), 1.22 (1.04–1.44), and 1.38 (1.06–1.80), respectively, but the suggested multiplicative interaction was not significant. Conclusions—FTO rs9939609 A-allele carriers have an increased CHD risk, and the association is not counteracted by increased physical activity. (Circ Cardiovasc Genet. 2014;7:171-177.) Key Words: coronary disease ◼ molecular epidemiology ◼ motor activity
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ardiovascular disease, obesity, and metabolic syndrome are interrelated and develop through the complex interplay among genetic, lifestyle, and environmental factors. Since the discovery of variants in the fat mass– and obesity- associated gene (FTO) that predispose to obesity and type II diabetes mellitus mainly through an increase in fat mass,1–5 several studies have also shown association between FTO variants and cardiovascular disease.6–10 The exact mechanism by which FTO influences adiposity is unknown, but a central regulatory effect on appetite and energy intake has been suggested, whereas energy expenditure and physical activity (PA) levels seem unaffected.11–16 The minor allele A of the singlenucleotide polymorphism (SNP) rs9939609 (T>A) has been associated with an atherogenic lipid profile,6 elevated plasma C-reactive protein levels,17 and hypertension,18 and a study in >17 000 Europeans showed that the FTO association with a range of metabolic measures (including low-density lipoprotein cholesterol [LDL-C] and high-density lipoprotein cholesterol, triglycerides, glucose, and insulin) was entirely because of its effect on body mass index (BMI).19 Several studies
suggest that the FTO association with cardiovascular disease is not entirely mediated by BMI or other obesity-related factors.6–10 However, it is unknown whether there are additional effects of FTO that could explain the association with cardiovascular disease.
Clinical Perspective on p 177 The effect of gene variants on cardiovascular disease may be modified by lifestyle factors, potentially making the contribution of any specific gene variant context-dependent. A recent meta-analysis found that increased PA attenuates the association of FTO with obesity.20 However, there are few publications on whether PA also modifies the FTO association with cardiovascular disease. In a study of white women in the United States, the risk allele of the FTO SNP rs8050136, which is in complete linkage disequilibrium with rs9939609 in whites,21 was associated with increased cardiovascular disease risk only in less physically active women.9 In contrast, a study in a Swedish cohort showed that lower PA levels were associated with increased cardiovascular mortality in
Received December 3, 2012; accepted February 25, 2014. From the Occupational and Environmental Medicine (J.G., F.N.), Public Health Epidemiology, Department of Public Health and Community Medicine (K.M., L.L.), and Department of Molecular and Clinical Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden (L.B., A.R.); Division of Cardiovascular Epidemiology, Institute of Environmental Medicine, Karolinska Institute, Stockholm, Sweden (K.L.); and AstraZeneca R&D, Mölndal, Sweden (F.N.). The Data Supplement is available at http://circgenetics.ahajournals.org/lookup/suppl/doi:10.1161/CIRCGENETICS.111.000007/-/DC1. Correspondence to Jaana Gustavsson, MSc, Occupational and Environmental Medicine Unit, Department of Public Health and Community Medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Box 414, SE 405 30, Gothenburg, Sweden. E-mail [email protected] © 2014 American Heart Association, Inc. Circ Cardiovasc Genet is available at http://circgenetics.ahajournals.org
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172 Circ Cardiovasc Genet April 2014 subjects with the FTO rs9939609 TT genotype but not in A risk allele carriers, suggesting a reduced genetic risk contrast in less physically active people.22 From these studies, it is unclear whether increased PA reduces the FTO association with cardiovascular disease as suggested for its effect on BMI. Therefore, our aim was to examine the association between the FTO rs9939609 variant and coronary heart disease (CHD) and determine whether PA modifies the association and, in particular, whether increased PA can protect against the genetic risk caused by FTO.
Methods Study Sample Two Swedish population–based case–control studies, INTERplay between GENEtic susceptibility and environmental factors for the risk of chronic diseases in West Sweden (INTERGENE) and Stockholm Heart Epidemiology Program (SHEEP), were pooled but also analyzed separately. The study designs have been described in detail previously.23–25 Briefly, INTERGENE included a cohort of 3614 randomly selected subjects aged 25 to 74 years and living in the greater Gothenburg region on April 1, 2001. These control subjects were examined during the period April 2001 to April 2004. During the same time period, patients discharged with a diagnosis of CHD in the same region were identified, and 618 cases surviving ≥21 days after hospitalization were recruited to the study. Of these, 192 had a first-time myocardial infarction (MI), 79 had a first-time episode of unstable angina pectoris, and 24 had chronic angina and a positive angiogram, whereas the remaining 323 cases had a previous history of CHD and had sought emergency care for cardiac symptoms. The SHEEP study investigated Swedish citizens aged 45 to 70 years living in Stockholm County during 1992 to 1994 and included 1213 cases of first-time acute MI surviving ≥28 days after their MI and 1561 randomly selected population controls free from MI diagnosis and matched for age, sex, and hospital catchment area. Both studies were approved by local ethics committees, and study subjects gave informed consent before participation. In the current study, we included in total 6145 subjects with known genotype at SNP rs9939609, including 3568 subjects (610 cases) from INTERGENE and 2577 subjects (1133 cases) from SHEEP.
Phenotypic Assessment All participants underwent clinical examinations, including measurement of height to the nearest 1 cm, weight to the nearest 0.1 kg, and measurement of waist and hip circumference to the nearest 1 cm while wearing light clothing and no shoes. The waist–hip ratio was defined as the ratio between the waist and hip circumference. Blood samples for standard laboratory tests and genotyping were collected after a 4-hour fast. Serum cholesterol and triglyceride concentrations were determined using enzymatic assays. LDL-C levels were estimated according to the Friedewald formula. BMI was defined as weight divided by height in square meters (kg∙m−2). Overweight and obesity were defined as BMI≥25 and ≥30, respectively. Lifestyle data, including leisure time PA and smoking habits, were collected in self-administered questionnaires. The INTERGENE question on leisure time PA during the past year included 4 categories: (1) mainly sitting (eg, reading, watching TV, computers, or other sitting activity); (2) moderate exercise (walking, cycling, or other physical activity, eg, gardening ≥4 hours a week); (3) regular exercise (eg, running, tennis, swimming ≥2–3 hours a week); and (4) hard training (at competitive level several times a week).26 The SHEEP question on weekly leisure time PA during different 10or 5-year age intervals also included 4 categories: (1) very little physical activity, (2) occasional walks, (3) exercise (defined as ≥30 minutes of activity involving breathlessness) now and then, and (4) regular exercise (at least once per week). The data acquired from the SHEEP study were based on the latest reported age interval, which
included ≤10 years preceding the age at reporting. For the current analysis, we categorized leisure time PA into 3 levels: low PA including categories 1 from INTERGENE (mainly sitting) and 1 (very little physical activity) from SHEEP; medium PA including categories 2 (moderate exercise) from INTERGENE and 2 (occasional walks) + 3 (now and then) from SHEEP; and high PA including categories 3 (regular) + 4 (hard training) from INTERGENE and 4 (regular) from SHEEP. We also used a dichotomous PA variable for sensitivity analyses, where the inactive group corresponded to the low PA level and the active group corresponded to the medium/high PA levels combined. Smoking was categorized into current, past, or nonsmokers. Current smokers were those reporting current regular smoking and included those who quit regular smoking 22 000 men and women in Sweden, which showed that subjects with the normal-risk TT genotype had a more pronounced increase in cardiovascular mortality associated with decreased PA than subjects carrying the A allele.22 In contrast to these findings, a prospective study in >21 000 white women in the United States demonstrated that only less physically active women had an increased risk of cardiovascular events associated with the FTO rs8050136 risk (A) allele.9 These contrasting results are not easily explained, but there are several differences in study design that may contribute to making the results less comparable. First, the study populations are from different geographical regions with different lifestyle and environment contexts, and the US study included only women. It is probable that leisure time PA habits covary with other lifestyle factors (eg, diet), and such covariation may have different patterns in different regions. Thus, it cannot be ruled out that the reported interactions between PA and FTO genotype are at least partly because of some other correlating factor. Another difference between our study and the study conducted in the United States concerns the definition of PA. They used a dichotomous PA variable based on a continuous score of leisure time PA with the median activity level as cut point, dividing the study cohort into 2 groups of equal size. Our PA variables were based on a categorical scale of leisure time PA, and the definition of low activity only included subjects with a sedentary leisure time, probably yielding a more homogenous group of inactive subjects than if using the median activity level as a cut point. Finally, 2 different SNPs were studied, but because rs9939609 and rs8050136 are in complete linkage disequilibrium in whites,21 they are expected to be comparable. The overall FTO effect on BMI in our study was consistent with literature, and we also found a trend of weaker FTO effect on BMI in more physically active control subjects than in less active subjects, which agrees with a meta-analysis concluding that increased PA attenuates the FTO effect on BMI and obesity.20 Of note, the meta-analysis found a stronger interaction in the Northern American populations than in the European populations comprising >44 000 individuals, where the interaction was not significant. The reason for this difference between geographic regions was not clarified, but a difference in traditions of measuring PA levels was suggested as 1 contributing factor. Interestingly, the FTO–PA interaction pattern with respect to BMI goes in the opposite direction to the pattern we observed between FTO and PA on CHD risk. This implies that although increased PA may counteract the effect of FTO risk variants on obesity, it may not necessarily attenuate the FTO association with cardiovascular disease. Our study has both strengths and limitations to be considered. One of the key strengths is the access to standardized and detailed lifestyle data and cardiovascular risk factors in 2 separate case–control samples in Sweden, enabling analysis of gene–environment interaction. The findings in both original samples analyzed separately were similar, which adds credibility to our conclusions. In sensitivity analyses
excluding cases with previous history of CHD, the association between FTO genotype and CHD risk was strengthened despite a smaller sample size, which also lends support to the FTO–CHD association. Among study limitations is the retrospective self-reporting of PA, which is subject to potential recall or reporting bias because of knowledge of disease in the cases. Another limitation is a potential misclassification of PA level over time. The average weekly leisure time activity was reported for rather long periods, and the level of PA may have varied considerably during this period. However, this potential misclassification is expected to be essentially nondifferential for cases and controls. Furthermore, the questions in the 2 original studies were not identical, and the 3 defined activity levels may not have been fully comparable between the 2 samples. However, the ranking of subjects within each study is likely valid, and because the PA level associations with CHD were similar when we analyzed the study samples separately, we think that this was of limited importance. In addition, the sensitivity interaction analysis in which we used a dichotomous PA variable showed a similar pattern as with the 3-level PA variable, confirming the robustness of the interaction analysis to different groupings of PA. Furthermore, we did not include data on occupational activity, which contributes to the total activity level. However, a previous study has shown that increased leisure time PA is a strong preventive factor of MI, irrespective of other forms of activity at home or at work.32 Another study showed that occupational activity was more subject to recall bias than leisure time PA, supporting that leisure time activity is an appropriate and accurate measure of PA in a study of the current design.33 Finally, fatal CHD cases were not included in the study sample, which may affect the estimated association between FTO genotype and CHD risk. To conclude, this study shows that carriers of the FTO rs9939609 A allele are at increased risk of CHD compared with noncarriers, and this seems not entirely explained by an increase in BMI. In addition, a higher PA level does not seem to protect from the CHD risk attributable to FTO genotype, and thus the public health interpretation is that the relatively small increase in CHD risk associated with the risk FTO genotype is similar for people with different PA levels.
Sources of Funding The research was funded by grants from the Västra Götaland County Council, the Swedish Council for Working Life and Social Research, the Swedish Research Council, the Swedish Research Council for Environment and Spatial Planning, the Swedish Heart and Lung Foundation, and AstraZeneca R&D Sweden.
Disclosures None.
References 1. Frayling TM, Timpson NJ, Weedon MN, Zeggini E, Freathy RM, Lindgren CM, et al. A common variant in the FTO gene is associated with body mass index and predisposes to childhood and adult obesity. Science. 2007;316:889–894. 2. Scott LJ, Mohlke KL, Bonnycastle LL, Willer CJ, Li Y, Duren WL, et al. A genome-wide association study of type 2 diabetes in Finns detects multiple susceptibility variants. Science. 2007;316:1341–1345.
Gustavsson et al FTO, Physical Activity, and Coronary Heart Disease 177 3. Dina C, Meyre D, Gallina S, Durand E, Körner A, Jacobson P, et al. Variation in FTO contributes to childhood obesity and severe adult obesity. Nat Genet. 2007;39:724–726. 4. Scuteri A, Sanna S, Chen WM, Uda M, Albai G, Strait J, et al. Genome- wide association scan shows genetic variants in the FTO gene are associated with obesity-related traits. PLoS Genet. 2007;3:e115. 5. Hunt SC, Stone S, Xin Y, Scherer CA, Magness CL, Iadonato SP, et al. Association of the FTO gene with BMI. Obesity (Silver Spring). 2008;16:902–904. 6. Doney AS, Dannfald J, Kimber CH, Donnelly LA, Pearson E, Morris AD, et al. The FTO gene is associated with an atherogenic lipid profile and myocardial infarction in patients with type 2 diabetes: a Genetics of Diabetes Audit and Research Study in Tayside Scotland (Go-DARTS) study. Circ Cardiovasc Genet. 2009;2:255–259. 7. He M, Cornelis MC, Franks PW, Zhang C, Hu FB, Qi L. Obesity genotype score and cardiovascular risk in women with type 2 diabetes mellitus. Arterioscler Thromb Vasc Biol. 2010;30:327–332. 8. Hubacek JA, Stanek V, Gebauerová M, Pilipcincová A, Dlouhá D, Poledne R, et al. A FTO variant and risk of acute coronary syndrome. Clin Chim Acta. 2010;411:1069–1072. 9. Ahmad T, Chasman DI, Mora S, Paré G, Cook NR, Buring JE, et al. The fat-mass and obesity-associated (FTO) gene, physical activity, and risk of incident cardiovascular events in white women. Am Heart J. 2010;160:1163–1169. 10. Lappalainen T, Kolehmainen M, Schwab US, Tolppanen AM, Stančáková A, Lindström J, et al.; Finnish Diabetes Prevention Study Group. Association of the FTO gene variant (rs9939609) with cardiovascular disease in men with abnormal glucose metabolism—the Finnish Diabetes Prevention Study. Nutr Metab Cardiovasc Dis. 2011;21:691–698. 11. Fredriksson R, Hägglund M, Olszewski PK, Stephansson O, Jacobsson JA, Olszewska AM, et al. The obesity gene, FTO, is of ancient origin, up-regulated during food deprivation and expressed in neurons of feeding- related nuclei of the brain. Endocrinology. 2008;149:2062–2071. 12. Berentzen T, Kring SI, Holst C, Zimmermann E, Jess T, Hansen T, et al. Lack of association of fatness-related FTO gene variants with energy expenditure or physical activity. J Clin Endocrinol Metab. 2008;93:2904–2908. 13. Speakman JR, Rance KA, Johnstone AM. Polymorphisms of the FTO gene are associated with variation in energy intake, but not energy expenditure. Obesity (Silver Spring). 2008;16:1961–1965. 14. Olszewski PK, Fredriksson R, Olszewska AM, Stephansson O, Alsiö J, Radomska KJ, et al. Hypothalamic FTO is associated with the regulation of energy intake not feeding reward. BMC Neurosci. 2009;10:129. 15. Hakanen M, Raitakari OT, Lehtimäki T, Peltonen N, Pahkala K, Sillanmäki L, et al. FTO genotype is associated with body mass index after the age of seven years but not with energy intake or leisure-time physical activity. J Clin Endocrinol Metab. 2009;94:1281–1287. 16. Speakman JR. FTO effect on energy demand versus food intake. Nature. 2010;464:E1; discussion E2. 17. Fisher E, Schulze MB, Stefan N, Häring HU, Döring F, Joost HG, et al. Association of the FTO rs9939609 single nucleotide polymorphism with C-reactive protein levels. Obesity (Silver Spring). 2009;17:330–334.
18. Pausova Z, Syme C, Abrahamowicz M, Xiao Y, Leonard GT, Perron M, et al. A common variant of the FTO gene is associated with not only increased adiposity but also elevated blood pressure in French Canadians. Circ Cardiovasc Genet. 2009;2:260–269. 19. Freathy RM, Timpson NJ, Lawlor DA, Pouta A, Ben-Shlomo Y, Ruokonen A, et al. Common variation in the FTO gene alters diabetes-related metabolic traits to the extent expected given its effect on BMI. Diabetes. 2008;57:1419–1426. 20. Kilpeläinen TO, Qi L, Brage S, Sharp SJ, Sonestedt E, Demerath E, et al. Physical activity attenuates the influence of FTO variants on obesity risk: a meta-analysis of 218,166 adults and 19,268 children. PLoS Med. 2011;8:e1001116. 21. Grant SF, Li M, Bradfield JP, Kim CE, Annaiah K, Santa E, et al. Association analysis of the FTO gene with obesity in children of Caucasian and African ancestry reveals a common tagging SNP. PLoS One. 2008;3:e1746. 22. Sonestedt E, Gullberg B, Ericson U, Wirfält E, Hedblad B, Orho-Melander M. Association between fat intake, physical activity and mortality depending on genetic variation in FTO. Int J Obes (Lond). 2011; 35:1041–1049. 23. Berg CM, Lappas G, Strandhagen E, Wolk A, Torén K, Rosengren A, et al. Food patterns and cardiovascular disease risk factors: the Swedish INTERGENE research program. Am J Clin Nutr. 2008;88:289–297. 24. Berg CM, Lissner L, Aires N, Lappas G, Torén K, Wilhelmsen L, et al. Trends in blood lipid levels, blood pressure, alcohol and smoking habits from 1985 to 2002: results from INTERGENE and GOT-MONICA. Eur J Cardiovasc Prev Rehabil. 2005;12:115–125. 25. Reuterwall C, Hallqvist J, Ahlbom A, De Faire U, Diderichsen F, Hogstedt C, et al. Higher relative, but lower absolute risks of myocardial infarction in women than in men: analysis of some major risk factors in the SHEEP study: the SHEEP Study Group. J Intern Med. 1999;246:161–174. 26. Aires N, Selmer R, Thelle D. The validity of self-reported leisure time physical activity, and its relationship to serum cholesterol, blood pressure and body mass index. A population based study of 332,182 men and women aged 40-42 years. Eur J Epidemiol. 2003;18:479–485. 27. Pearce N. What does the odds ratio estimate in a case-control study? Int J Epidemiol. 1993;22:1189–1192. 28. Rothman KJ. Measuring interactions. In: Epidemiology: An Introduction. New York, NY: Oxford University Press; 2002:168–180. 29. Zou GY. On the estimation of additive interaction by use of the four-by- two table and beyond. Am J Epidemiol. 2008;168:212–224. 30. Harris RJ, Bradburn MJ, Deeks JJ, Altman DG, Harbord RM, Sterne JAC. Metan: fixed- and random-effects meta-analysis. Stata Journal. 2008;8:3–28. 31. Knol MJ, VanderWeele TJ. Recommendations for presenting analyses of effect modification and interaction. Int J Epidemiol. 2012;41:514–520. 32. Fransson E, De Faire U, Ahlbom A, Reuterwall C, Hallqvist J, Alfredsson L. The risk of acute myocardial infarction: interactions of types of physical activity. Epidemiology. 2004;15:573–582. 33. Fransson E, Knutsson A, Westerholm P, Alfredsson L. Indications of recall bias found in a retrospective study of physical activity and myocardial infarction. J Clin Epidemiol. 2008;61:840–847.
CLINICAL PERSPECTIVE Since the discovery that common variation in the fat mass– and obesity-associated gene (FTO) gene predisposes to obesity and type 2 diabetes mellitus, mainly through an increase in fat mass, an association has also been found with cardiovascular disease (CVD). However, it seems that the increased CVD risk is not entirely explained by obesity-related traits. The FTO gene is a neuropeptide expressed in the hypothalamus, with a suggested role in energy homeostasis and possibly appetite regulation. Studies have shown that carriers of the FTO risk variants have a preference for energy-dense foods. The gene is also expressed in peripheral nerves and may have additional, yet unknown, physiological effects. The FTO gene effect on obesity and CVD may be modified by lifestyle factors, such as exercise or diet. Physical activity has been suggested to reduce the FTO effect on obesity so that an association between FTO risk variants and obesity is only seen in sedentary people. However, there is controversy between reports, and a possible effect modification in CVD has not been explored. The current study demonstrates an ≈20% increased risk of coronary heart disease in people carrying ≥1 FTO risk allele, even after adjustment for body mass index. The level of physical activity did not change the absolute coronary heart disease risk from FTO. This suggests that a higher physical activity level, although beneficial for health in general, does not protect from the relatively small increase in CVD risk that is attributable to FTO gene variants.
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ardiovascular disease, obesity, and metabolic syndrome are interrelated and develop through the complex interplay among genetic, lifestyle, and environmental factors. Since the discovery of variants in the fat mass– and obesity- associated gene (FTO) that predispose to obesity and type II diabetes mellitus mainly through an increase in fat mass,1–5 several studies have also shown association between FTO variants and cardiovascular disease.6–10 The exact mechanism by which FTO influences adiposity is unknown, but a central regulatory effect on appetite and energy intake has been suggested, whereas energy expenditure and physical activity (PA) levels seem unaffected.11–16 The minor allele A of the singlenucleotide polymorphism (SNP) rs9939609 (T>A) has been associated with an atherogenic lipid profile,6 elevated plasma C-reactive protein levels,17 and hypertension,18 and a study in >17 000 Europeans showed that the FTO association with a range of metabolic measures (including low-density lipoprotein cholesterol [LDL-C] and high-density lipoprotein cholesterol, triglycerides, glucose, and insulin) was entirely because of its effect on body mass index (BMI).19 Several studies
suggest that the FTO association with cardiovascular disease is not entirely mediated by BMI or other obesity-related factors.6–10 However, it is unknown whether there are additional effects of FTO that could explain the association with cardiovascular disease.
Clinical Perspective on p 177 The effect of gene variants on cardiovascular disease may be modified by lifestyle factors, potentially making the contribution of any specific gene variant context-dependent. A recent meta-analysis found that increased PA attenuates the association of FTO with obesity.20 However, there are few publications on whether PA also modifies the FTO association with cardiovascular disease. In a study of white women in the United States, the risk allele of the FTO SNP rs8050136, which is in complete linkage disequilibrium with rs9939609 in whites,21 was associated with increased cardiovascular disease risk only in less physically active women.9 In contrast, a study in a Swedish cohort showed that lower PA levels were associated with increased cardiovascular mortality in
Received December 3, 2012; accepted February 25, 2014. From the Occupational and Environmental Medicine (J.G., F.N.), Public Health Epidemiology, Department of Public Health and Community Medicine (K.M., L.L.), and Department of Molecular and Clinical Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden (L.B., A.R.); Division of Cardiovascular Epidemiology, Institute of Environmental Medicine, Karolinska Institute, Stockholm, Sweden (K.L.); and AstraZeneca R&D, Mölndal, Sweden (F.N.). The Data Supplement is available at http://circgenetics.ahajournals.org/lookup/suppl/doi:10.1161/CIRCGENETICS.111.000007/-/DC1. Correspondence to Jaana Gustavsson, MSc, Occupational and Environmental Medicine Unit, Department of Public Health and Community Medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Box 414, SE 405 30, Gothenburg, Sweden. E-mail [email protected] © 2014 American Heart Association, Inc. Circ Cardiovasc Genet is available at http://circgenetics.ahajournals.org
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172 Circ Cardiovasc Genet April 2014 subjects with the FTO rs9939609 TT genotype but not in A risk allele carriers, suggesting a reduced genetic risk contrast in less physically active people.22 From these studies, it is unclear whether increased PA reduces the FTO association with cardiovascular disease as suggested for its effect on BMI. Therefore, our aim was to examine the association between the FTO rs9939609 variant and coronary heart disease (CHD) and determine whether PA modifies the association and, in particular, whether increased PA can protect against the genetic risk caused by FTO.
Methods Study Sample Two Swedish population–based case–control studies, INTERplay between GENEtic susceptibility and environmental factors for the risk of chronic diseases in West Sweden (INTERGENE) and Stockholm Heart Epidemiology Program (SHEEP), were pooled but also analyzed separately. The study designs have been described in detail previously.23–25 Briefly, INTERGENE included a cohort of 3614 randomly selected subjects aged 25 to 74 years and living in the greater Gothenburg region on April 1, 2001. These control subjects were examined during the period April 2001 to April 2004. During the same time period, patients discharged with a diagnosis of CHD in the same region were identified, and 618 cases surviving ≥21 days after hospitalization were recruited to the study. Of these, 192 had a first-time myocardial infarction (MI), 79 had a first-time episode of unstable angina pectoris, and 24 had chronic angina and a positive angiogram, whereas the remaining 323 cases had a previous history of CHD and had sought emergency care for cardiac symptoms. The SHEEP study investigated Swedish citizens aged 45 to 70 years living in Stockholm County during 1992 to 1994 and included 1213 cases of first-time acute MI surviving ≥28 days after their MI and 1561 randomly selected population controls free from MI diagnosis and matched for age, sex, and hospital catchment area. Both studies were approved by local ethics committees, and study subjects gave informed consent before participation. In the current study, we included in total 6145 subjects with known genotype at SNP rs9939609, including 3568 subjects (610 cases) from INTERGENE and 2577 subjects (1133 cases) from SHEEP.
Phenotypic Assessment All participants underwent clinical examinations, including measurement of height to the nearest 1 cm, weight to the nearest 0.1 kg, and measurement of waist and hip circumference to the nearest 1 cm while wearing light clothing and no shoes. The waist–hip ratio was defined as the ratio between the waist and hip circumference. Blood samples for standard laboratory tests and genotyping were collected after a 4-hour fast. Serum cholesterol and triglyceride concentrations were determined using enzymatic assays. LDL-C levels were estimated according to the Friedewald formula. BMI was defined as weight divided by height in square meters (kg∙m−2). Overweight and obesity were defined as BMI≥25 and ≥30, respectively. Lifestyle data, including leisure time PA and smoking habits, were collected in self-administered questionnaires. The INTERGENE question on leisure time PA during the past year included 4 categories: (1) mainly sitting (eg, reading, watching TV, computers, or other sitting activity); (2) moderate exercise (walking, cycling, or other physical activity, eg, gardening ≥4 hours a week); (3) regular exercise (eg, running, tennis, swimming ≥2–3 hours a week); and (4) hard training (at competitive level several times a week).26 The SHEEP question on weekly leisure time PA during different 10or 5-year age intervals also included 4 categories: (1) very little physical activity, (2) occasional walks, (3) exercise (defined as ≥30 minutes of activity involving breathlessness) now and then, and (4) regular exercise (at least once per week). The data acquired from the SHEEP study were based on the latest reported age interval, which
included ≤10 years preceding the age at reporting. For the current analysis, we categorized leisure time PA into 3 levels: low PA including categories 1 from INTERGENE (mainly sitting) and 1 (very little physical activity) from SHEEP; medium PA including categories 2 (moderate exercise) from INTERGENE and 2 (occasional walks) + 3 (now and then) from SHEEP; and high PA including categories 3 (regular) + 4 (hard training) from INTERGENE and 4 (regular) from SHEEP. We also used a dichotomous PA variable for sensitivity analyses, where the inactive group corresponded to the low PA level and the active group corresponded to the medium/high PA levels combined. Smoking was categorized into current, past, or nonsmokers. Current smokers were those reporting current regular smoking and included those who quit regular smoking 22 000 men and women in Sweden, which showed that subjects with the normal-risk TT genotype had a more pronounced increase in cardiovascular mortality associated with decreased PA than subjects carrying the A allele.22 In contrast to these findings, a prospective study in >21 000 white women in the United States demonstrated that only less physically active women had an increased risk of cardiovascular events associated with the FTO rs8050136 risk (A) allele.9 These contrasting results are not easily explained, but there are several differences in study design that may contribute to making the results less comparable. First, the study populations are from different geographical regions with different lifestyle and environment contexts, and the US study included only women. It is probable that leisure time PA habits covary with other lifestyle factors (eg, diet), and such covariation may have different patterns in different regions. Thus, it cannot be ruled out that the reported interactions between PA and FTO genotype are at least partly because of some other correlating factor. Another difference between our study and the study conducted in the United States concerns the definition of PA. They used a dichotomous PA variable based on a continuous score of leisure time PA with the median activity level as cut point, dividing the study cohort into 2 groups of equal size. Our PA variables were based on a categorical scale of leisure time PA, and the definition of low activity only included subjects with a sedentary leisure time, probably yielding a more homogenous group of inactive subjects than if using the median activity level as a cut point. Finally, 2 different SNPs were studied, but because rs9939609 and rs8050136 are in complete linkage disequilibrium in whites,21 they are expected to be comparable. The overall FTO effect on BMI in our study was consistent with literature, and we also found a trend of weaker FTO effect on BMI in more physically active control subjects than in less active subjects, which agrees with a meta-analysis concluding that increased PA attenuates the FTO effect on BMI and obesity.20 Of note, the meta-analysis found a stronger interaction in the Northern American populations than in the European populations comprising >44 000 individuals, where the interaction was not significant. The reason for this difference between geographic regions was not clarified, but a difference in traditions of measuring PA levels was suggested as 1 contributing factor. Interestingly, the FTO–PA interaction pattern with respect to BMI goes in the opposite direction to the pattern we observed between FTO and PA on CHD risk. This implies that although increased PA may counteract the effect of FTO risk variants on obesity, it may not necessarily attenuate the FTO association with cardiovascular disease. Our study has both strengths and limitations to be considered. One of the key strengths is the access to standardized and detailed lifestyle data and cardiovascular risk factors in 2 separate case–control samples in Sweden, enabling analysis of gene–environment interaction. The findings in both original samples analyzed separately were similar, which adds credibility to our conclusions. In sensitivity analyses
excluding cases with previous history of CHD, the association between FTO genotype and CHD risk was strengthened despite a smaller sample size, which also lends support to the FTO–CHD association. Among study limitations is the retrospective self-reporting of PA, which is subject to potential recall or reporting bias because of knowledge of disease in the cases. Another limitation is a potential misclassification of PA level over time. The average weekly leisure time activity was reported for rather long periods, and the level of PA may have varied considerably during this period. However, this potential misclassification is expected to be essentially nondifferential for cases and controls. Furthermore, the questions in the 2 original studies were not identical, and the 3 defined activity levels may not have been fully comparable between the 2 samples. However, the ranking of subjects within each study is likely valid, and because the PA level associations with CHD were similar when we analyzed the study samples separately, we think that this was of limited importance. In addition, the sensitivity interaction analysis in which we used a dichotomous PA variable showed a similar pattern as with the 3-level PA variable, confirming the robustness of the interaction analysis to different groupings of PA. Furthermore, we did not include data on occupational activity, which contributes to the total activity level. However, a previous study has shown that increased leisure time PA is a strong preventive factor of MI, irrespective of other forms of activity at home or at work.32 Another study showed that occupational activity was more subject to recall bias than leisure time PA, supporting that leisure time activity is an appropriate and accurate measure of PA in a study of the current design.33 Finally, fatal CHD cases were not included in the study sample, which may affect the estimated association between FTO genotype and CHD risk. To conclude, this study shows that carriers of the FTO rs9939609 A allele are at increased risk of CHD compared with noncarriers, and this seems not entirely explained by an increase in BMI. In addition, a higher PA level does not seem to protect from the CHD risk attributable to FTO genotype, and thus the public health interpretation is that the relatively small increase in CHD risk associated with the risk FTO genotype is similar for people with different PA levels.
Sources of Funding The research was funded by grants from the Västra Götaland County Council, the Swedish Council for Working Life and Social Research, the Swedish Research Council, the Swedish Research Council for Environment and Spatial Planning, the Swedish Heart and Lung Foundation, and AstraZeneca R&D Sweden.
Disclosures None.
References 1. Frayling TM, Timpson NJ, Weedon MN, Zeggini E, Freathy RM, Lindgren CM, et al. A common variant in the FTO gene is associated with body mass index and predisposes to childhood and adult obesity. Science. 2007;316:889–894. 2. Scott LJ, Mohlke KL, Bonnycastle LL, Willer CJ, Li Y, Duren WL, et al. A genome-wide association study of type 2 diabetes in Finns detects multiple susceptibility variants. Science. 2007;316:1341–1345.
Gustavsson et al FTO, Physical Activity, and Coronary Heart Disease 177 3. Dina C, Meyre D, Gallina S, Durand E, Körner A, Jacobson P, et al. Variation in FTO contributes to childhood obesity and severe adult obesity. Nat Genet. 2007;39:724–726. 4. Scuteri A, Sanna S, Chen WM, Uda M, Albai G, Strait J, et al. Genome- wide association scan shows genetic variants in the FTO gene are associated with obesity-related traits. PLoS Genet. 2007;3:e115. 5. Hunt SC, Stone S, Xin Y, Scherer CA, Magness CL, Iadonato SP, et al. Association of the FTO gene with BMI. Obesity (Silver Spring). 2008;16:902–904. 6. Doney AS, Dannfald J, Kimber CH, Donnelly LA, Pearson E, Morris AD, et al. The FTO gene is associated with an atherogenic lipid profile and myocardial infarction in patients with type 2 diabetes: a Genetics of Diabetes Audit and Research Study in Tayside Scotland (Go-DARTS) study. Circ Cardiovasc Genet. 2009;2:255–259. 7. He M, Cornelis MC, Franks PW, Zhang C, Hu FB, Qi L. Obesity genotype score and cardiovascular risk in women with type 2 diabetes mellitus. Arterioscler Thromb Vasc Biol. 2010;30:327–332. 8. Hubacek JA, Stanek V, Gebauerová M, Pilipcincová A, Dlouhá D, Poledne R, et al. A FTO variant and risk of acute coronary syndrome. Clin Chim Acta. 2010;411:1069–1072. 9. Ahmad T, Chasman DI, Mora S, Paré G, Cook NR, Buring JE, et al. The fat-mass and obesity-associated (FTO) gene, physical activity, and risk of incident cardiovascular events in white women. Am Heart J. 2010;160:1163–1169. 10. Lappalainen T, Kolehmainen M, Schwab US, Tolppanen AM, Stančáková A, Lindström J, et al.; Finnish Diabetes Prevention Study Group. Association of the FTO gene variant (rs9939609) with cardiovascular disease in men with abnormal glucose metabolism—the Finnish Diabetes Prevention Study. Nutr Metab Cardiovasc Dis. 2011;21:691–698. 11. Fredriksson R, Hägglund M, Olszewski PK, Stephansson O, Jacobsson JA, Olszewska AM, et al. The obesity gene, FTO, is of ancient origin, up-regulated during food deprivation and expressed in neurons of feeding- related nuclei of the brain. Endocrinology. 2008;149:2062–2071. 12. Berentzen T, Kring SI, Holst C, Zimmermann E, Jess T, Hansen T, et al. Lack of association of fatness-related FTO gene variants with energy expenditure or physical activity. J Clin Endocrinol Metab. 2008;93:2904–2908. 13. Speakman JR, Rance KA, Johnstone AM. Polymorphisms of the FTO gene are associated with variation in energy intake, but not energy expenditure. Obesity (Silver Spring). 2008;16:1961–1965. 14. Olszewski PK, Fredriksson R, Olszewska AM, Stephansson O, Alsiö J, Radomska KJ, et al. Hypothalamic FTO is associated with the regulation of energy intake not feeding reward. BMC Neurosci. 2009;10:129. 15. Hakanen M, Raitakari OT, Lehtimäki T, Peltonen N, Pahkala K, Sillanmäki L, et al. FTO genotype is associated with body mass index after the age of seven years but not with energy intake or leisure-time physical activity. J Clin Endocrinol Metab. 2009;94:1281–1287. 16. Speakman JR. FTO effect on energy demand versus food intake. Nature. 2010;464:E1; discussion E2. 17. Fisher E, Schulze MB, Stefan N, Häring HU, Döring F, Joost HG, et al. Association of the FTO rs9939609 single nucleotide polymorphism with C-reactive protein levels. Obesity (Silver Spring). 2009;17:330–334.
18. Pausova Z, Syme C, Abrahamowicz M, Xiao Y, Leonard GT, Perron M, et al. A common variant of the FTO gene is associated with not only increased adiposity but also elevated blood pressure in French Canadians. Circ Cardiovasc Genet. 2009;2:260–269. 19. Freathy RM, Timpson NJ, Lawlor DA, Pouta A, Ben-Shlomo Y, Ruokonen A, et al. Common variation in the FTO gene alters diabetes-related metabolic traits to the extent expected given its effect on BMI. Diabetes. 2008;57:1419–1426. 20. Kilpeläinen TO, Qi L, Brage S, Sharp SJ, Sonestedt E, Demerath E, et al. Physical activity attenuates the influence of FTO variants on obesity risk: a meta-analysis of 218,166 adults and 19,268 children. PLoS Med. 2011;8:e1001116. 21. Grant SF, Li M, Bradfield JP, Kim CE, Annaiah K, Santa E, et al. Association analysis of the FTO gene with obesity in children of Caucasian and African ancestry reveals a common tagging SNP. PLoS One. 2008;3:e1746. 22. Sonestedt E, Gullberg B, Ericson U, Wirfält E, Hedblad B, Orho-Melander M. Association between fat intake, physical activity and mortality depending on genetic variation in FTO. Int J Obes (Lond). 2011; 35:1041–1049. 23. Berg CM, Lappas G, Strandhagen E, Wolk A, Torén K, Rosengren A, et al. Food patterns and cardiovascular disease risk factors: the Swedish INTERGENE research program. Am J Clin Nutr. 2008;88:289–297. 24. Berg CM, Lissner L, Aires N, Lappas G, Torén K, Wilhelmsen L, et al. Trends in blood lipid levels, blood pressure, alcohol and smoking habits from 1985 to 2002: results from INTERGENE and GOT-MONICA. Eur J Cardiovasc Prev Rehabil. 2005;12:115–125. 25. Reuterwall C, Hallqvist J, Ahlbom A, De Faire U, Diderichsen F, Hogstedt C, et al. Higher relative, but lower absolute risks of myocardial infarction in women than in men: analysis of some major risk factors in the SHEEP study: the SHEEP Study Group. J Intern Med. 1999;246:161–174. 26. Aires N, Selmer R, Thelle D. The validity of self-reported leisure time physical activity, and its relationship to serum cholesterol, blood pressure and body mass index. A population based study of 332,182 men and women aged 40-42 years. Eur J Epidemiol. 2003;18:479–485. 27. Pearce N. What does the odds ratio estimate in a case-control study? Int J Epidemiol. 1993;22:1189–1192. 28. Rothman KJ. Measuring interactions. In: Epidemiology: An Introduction. New York, NY: Oxford University Press; 2002:168–180. 29. Zou GY. On the estimation of additive interaction by use of the four-by- two table and beyond. Am J Epidemiol. 2008;168:212–224. 30. Harris RJ, Bradburn MJ, Deeks JJ, Altman DG, Harbord RM, Sterne JAC. Metan: fixed- and random-effects meta-analysis. Stata Journal. 2008;8:3–28. 31. Knol MJ, VanderWeele TJ. Recommendations for presenting analyses of effect modification and interaction. Int J Epidemiol. 2012;41:514–520. 32. Fransson E, De Faire U, Ahlbom A, Reuterwall C, Hallqvist J, Alfredsson L. The risk of acute myocardial infarction: interactions of types of physical activity. Epidemiology. 2004;15:573–582. 33. Fransson E, Knutsson A, Westerholm P, Alfredsson L. Indications of recall bias found in a retrospective study of physical activity and myocardial infarction. J Clin Epidemiol. 2008;61:840–847.
CLINICAL PERSPECTIVE Since the discovery that common variation in the fat mass– and obesity-associated gene (FTO) gene predisposes to obesity and type 2 diabetes mellitus, mainly through an increase in fat mass, an association has also been found with cardiovascular disease (CVD). However, it seems that the increased CVD risk is not entirely explained by obesity-related traits. The FTO gene is a neuropeptide expressed in the hypothalamus, with a suggested role in energy homeostasis and possibly appetite regulation. Studies have shown that carriers of the FTO risk variants have a preference for energy-dense foods. The gene is also expressed in peripheral nerves and may have additional, yet unknown, physiological effects. The FTO gene effect on obesity and CVD may be modified by lifestyle factors, such as exercise or diet. Physical activity has been suggested to reduce the FTO effect on obesity so that an association between FTO risk variants and obesity is only seen in sedentary people. However, there is controversy between reports, and a possible effect modification in CVD has not been explored. The current study demonstrates an ≈20% increased risk of coronary heart disease in people carrying ≥1 FTO risk allele, even after adjustment for body mass index. The level of physical activity did not change the absolute coronary heart disease risk from FTO. This suggests that a higher physical activity level, although beneficial for health in general, does not protect from the relatively small increase in CVD risk that is attributable to FTO gene variants.
