Gene-Environment Interactions

1. Gene-Environment Interactions International Society for Nurses in Genetics May 2007 Jan Dorman, PhD University of Pittsburgh Pittsburgh, PA, USA

2. Objectives • Identify gene-environment interactions • Determine if the interaction follows an additive or multiplicative model • Assess the importance of the interaction for clinical practice • Apply ACMG guidelines for genetic testing for Factor V Leiden mutations and follow-up

3. Evidence of Gene-Environment Interactions • Familial aggregation of disease • Greater prevalence of disease in 1st degree relatives vs. spouses • Higher disease concordance among MZ vs. DZ twins • Earlier age at onset among familial vs. non-familial cases • Stronger phenotypic correlations between parents and biologic vs. adopted children

4. Evidence of Gene-Environment Interactions • International studies • Geographic variation in rates of disease • Temporal trends worldwide • Higher disease incidence among immigrants vs. source population • Age differences in risk depending on age at migration

5. Example: Multiple Sclerosis • Incidence is higher in countries far from the equator • High risk countries • US, Canada, Northern Europe • Low risk countries • Southern Europe, SE Asia, Africa

6. Incidence of MS per 100,000 / yr Among Immigrants to Israel Gordis, 1996

7. Gene-Environment Interactions • Often tested in case control studies • Require careful definitions of • Disorder (phenotype) • Environmental risk factors • High-risk genotypes (genetic susceptibility) • Stratify cases and controls • Susceptible • With / without exposure • Not susceptible • With / without exposure

8. Gene-Environment Interactions • Occur when the risk of disease in exposed and susceptible individuals differs fromthat expected based on their individual effects • Expected effects can be additive or multiplicative • Positive interaction • Synergistic • Negative interaction • Antagonistic

9. Gene-Environment Interactions

10. Gene-Environment Interactions Odds Ratio (OR) ah / bg ch / dg eh / fg 1

11. Example of Additive Effects S+E+21 7 S+E-15 5 S-E+ 9 3 S-E-3 1 Absolute Odds Strata Risk Difference Ratio 6 6

12. Example of Additive Effects OR Interaction = ORS+E+ - (ORS+E- + ORS-E+ - 1) If OR Interaction = 0, additive effects Example: OR Interaction=7 – (5 + 3 – 1) OR Interaction= 0 Effects are additive, which is expected

13. Example of Multiplicative Effects S+E+45 15 S+E-15 5 S-E+ 9 3 S-E-3 1 Absolute Odds Strata Risk Difference Ratio 3 3

14. Example of Multiplicative Effects OR Interaction = ORS+E+ / ORS+E- X ORS-E+ If OR Interaction = 1, multiplicative effects Example: OR Interaction = 15 / 5 x 3 OR Interaction= 1 Effects are multiplicative, which is expected

15. Advantages of 2 x 4 Table • Data displayed clearly and completely • OR for joint effects are readily generated and directly comparable • Based on same reference group • Can easily evaluate additive or multiplicative effects and identify interactions • Highlights sample size issues

16. Limitations of 2 x 4 Table • Only 2 risk factors are considered • Are not evaluating dose-response effects in exposure or susceptibility • Can only examine additive or multiplicative effects • Most gene-environment interactions are more complicated

17. Evaluating Gene-Environment Interactions – Clinical Example • Vandenbroucke JP, Koster T, Briet E, et al. Increased risk of venous thrombosis in oral contraceptive users who are carriers of factor V Leiden mutation. Lancet 1994; 344:1453-1547

18. Venous Thrombosis • Most frequent cardiovascular event in young women • Generally manifests as thrombosis of deep leg veins or pulmonary embolism • Incidence in women age 20-49 yrs is ~ 2 /10,000 persons/yr • Case fatality rate is ~ 1% to 2%

19. Oral Contraceptive Pills (OCP) and Venous Thrombosis (VT) • Association between OCP and VT has been known since early 1960s • Led to development of OCP with lower estrogen content • Incidence of VT is ~12 to 34 / 10,000 in OCP users • Risk of VTis highest during the 1st year of exposure

20. Factor V Leiden Mutations • R506Q mutation – amino acid substitution • Geographic variation in mutation prevalence • Frequency of the mutation in Caucasians is~2% to 10% • Rare in African and Asians • Prevalence among individuals with VT • 14% to 21% have the mutation • Relative risk of VT among carriers • 3- to 7-fold higher than non-carriers

21. OCP, Factor V Leiden Mutations and Venous Thrombosis • What is risk of venous thrombosis among women who use OCP and carry the mutation? • Is there a gene-environment interaction? • If so, what are the clinical implications?

22. OCP, Factor V Leiden Mutations and Venous Thrombosis OR (95% CI) 34.7 (7.8, 310.0) 6.9 (1,8, 31.8) 3.7 (1.2, 6.3) Reference Total 155 169 Lancet 1994;344:1453

23. Additive Effect? Strata OR S+E+ 34.7 S+E- 6.9 S-E+ 3.7 S-E- Ref OR Interaction = 34.7 – (6.9 + 3.7 - 1) = 25.1

24. Multiplicative Effect? Strata OR S+E+ 34.7 S+E- 6.9 S-E+ 3.7 S-E- Ref OR Interaction = 34.7 / 6.9 x 3.7 = 1.4

25. Prevalence of Mutation in Controls Used incidence of 2.1/10,000/yr to determine the number of person years that would be required for 155 new (incident) cases to develop. Used prevalence rates of mutation in controls to estimate the distribution of person years for each strata

26. Absolute Risk (Incidence) of VT *From formula presented in last lecture, R= 2/10.000/yr

27. Risk of VT per 10,000/year Bar represents background risk

28. Attributable Risk (AR) and Attributable Fraction (AF)

29. Genetic Testing for Factor V Leiden • Debate about the need to test for Factor V Leiden mutations before prescribing OCP • Mutation is prevalent (~2% to 10%) • May prevent death in carriers • Testing is readily available • May be appropriate for women with a positive family history • Offer genetic testing prior to prescribing OCP

30. Genetic Testing for Factor V Leiden • Arguments against genetic testing • Carriers will not receive OCP • Small number of deaths prevented • Results have implications for relatives • Possible insurance discrimination • Psychological distress/anxiety • False positive/negative results • Requires genetic counseling

31. Genetic Testing for Factor V Leiden • ACMG Recommendations • Age <50, any VT • VT in unusual sites • Recurrent VT • VT with positive family history • VT in a pregnant woman • VT in a women on OP • Relatives of individuals with VT <50 yrs • MI in women who smoke <50 yrs

32. Screening Questions Developed by Nurse Practitioners • Why do you want to be on HRT? • Have you had a blood clot? • Any family history of blood clots? • Any family history of stroke? • Lifestyle with prolonged immobility? • Breast, ovarian or cervical cancer? • Cancers in sister, mother, grandmother? • Any family history of CHD? If yes to #2-5, may be candidate for testing Park et al, 2003

33. Individuals with Factor V Leiden Mutation • Study of 110 mutation positive individuals identified in a North Carolina, US lab between 9/95 and 10/01 • Assessed knowledge; information needs, resources, satisfaction; health perception and anxiety; genetic testing issues • Quantitative and qualitative methods J Thromb Haemost 2003; 1:2335

34. Individuals with Factor V Leiden Mutation • Knowledge • 39% did not recall giving consent • 13% did not know that they carried the mutation (excluded) • 94% knew mutation increased risk for clots • 30% did not know to exercise/not smoke • 79% overestimated their risk of VT • 50% did not understand its inheritance

35. Individuals with Factor V Leiden Mutations • Satisfaction • 64% said they received little information • Varied according to seeing a hematologist • 40% satisfied if with hematologist • 19% satisfied if not with hematologist • 68% had many more questions • Confidence in providers knowledge • 65% for males • 33% for females

36. Individuals with Factor V Leiden Mutations • Information Needs • Most needed more information • 50% used internet as primary source • Health Perception • 28% spent much time trying to understand health implications • 51% made positive lifestyle changes • 43% reported increased worry • 85% were glad to know carrier status

37. Implications for Future • Patients interested in genetic testing for any condition need: • More information about genetic and environmental risk factors • Genetic counseling • Disclosure • Testing in children • Insurance discrimination • Other risks/benefits • Meaning of test results • Follow-up

38. Implications for Future • Nurses are key • Genetic epidemiology literature (estimates of OR and incidence rates) are useful resources for estimating risk associated with genetic and environmental risk factors

39. References • American College of Medical Genetics Consensus Statement on Factor V Leiden Mutation Testing. Genet Med 2001; 3:139-148. • Bank I, Scavenius MPRB, Buller H, et al. Social aspects of genetic testing for factor V leiden mutation in healthy individuals and their importance for daily practice. Thrombosis Research 2004; 113: 7-12.

40. References • Botto LD, Khoury MJ. Commentary: facing the challenge of gene-environment interaction: the 2 x 4 table. Am J Epidemiol 2001; 153:1016-1020 • Burton PR, Tobin MD, Hopper JL. Key concepts in genetic epidemiology. Lancet 2005; 366:941-951.

41. References • Clayton D, McKeigue PM. Epidemiological methods for studying genes and environmental factors in complex diseases. Lancet 2001; 358:1356-1360. • Gordis L. Epidemiology. WB Saunders Co., Phildelphia, 1996. • Hellmann EA, Leslie ND, Moll S. Knowledge and educational needs of individuals with the factor V Leiden mutation. J Thromb Haemost 2003; 1:2335-2339.

42. References • Horne MK and McCloskey DJ. Factor V Leiden as a common genetic risk factor for venous thromboembolism. J Nursing Scholarsh 2006; 38: 19-25. • Park BD, Lookinland S, Beckstrand RL, et al. Factor V Leiden and Venous Thromboembolism: risk Associated with Hormone Replacement Therapy. J Am Acad Nurse Pract 2004; 15:458-466.

43. References • Vandenbroucke JP, Koster T, Briet E, et al. Increased risk of venous thrombosis in oral contraceptive users who are carriers of factor V Leiden mutation. Lancet 1994; 344:1453-1547. • Vandenbroucke JP, van der Meer FJM, Helmerhorst FM, et al. Factor V Leiden: should we screen oral contraceptive users and pregnant women? BMJ 1996; 313:1127-1130.