Gene-Environment Interactions Nazarbayev University July 2012 Jan Dorman, PhD University of Pittsburgh Pittsburgh, PA, USA

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

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

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

Incidence of MS per 100,000 / yr Among Immigrants to Israel Age at Source Population Migration European Asian/African < 15 yrs yrs yrs Gordis, 1996

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

Gene-Environment Interactions Occur when the risk of disease in exposed and susceptible individuals differs from that expected based on their individual effects Positive interaction –Synergistic Negative interaction –Antagonistic

StrataCases (Affected) Controls (Unaffected) Susceptible & Exposed (S+E+) ab Susceptible & Not Exposed (S+E-) cd Not Susceptible & Exposed (S-E+) ef Not Susceptible & Not Exposed (S-E-) gh Gene-Environment Interactions

StrataCasesControls S+E+ ab S+E- cd S-E+ ef S-E- gh Odds Ratio (OR) ah / bg ch / dg eh / fg 1

Example of Additive Effects S + E S + E S - E + 93 S - E StrataRiskRatioDifference Absolute Odds Odds

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

Example of Multiplicative Effects S + E S + E S - E S - E StrataRiskDifference Absolute Ratio Odds Odds

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

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

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

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:

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

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 VT is highest during the 1 st year of exposure

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

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? OCP, Factor V Leiden Mutations and Venous Thrombosis

StrataCasesControls S+E+ 252 S+E- 104 S-E S-E OR (95% CI) 34.7 (7.8, 310.0) 6.9 (1,8, 31.8) 3.7 (1.2, 6.3) Reference Total Lancet 1994;344:1453

Additive Effects? Strata OR S+E S+E- 6.9 S-E+ 3.7 S-E- Ref OR Interaction = 34.7 – ( ) = 25.1

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

Absolute Risk What is absolute risk for S+E+? –Several ways to estimate –Population incidence = 2/10,000 PY 2 cases/10,000 PY = 155 cases / X PY X ~ 740,000 PY Distribute across strata –Absolute risk per strata # cases / PY

Person Years & Risk per Strata StrataNumber of Cases Prevalence Controls Person Years Risk/ 10,000/ yr S+E+251.1%8, S+E-102.4%17, S-E %276, S-E %438, Total %740,0002.1

Risk of VT per 10,000/year

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

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

Genetic Testing for Factor V Leiden ACMG Recommendations –Age <50, any VT –Recurrent VT –VT with positive family history –VT in a women on OP –Relatives of individuals with VT <50 yrs –MI in women who smoke <50 yrs

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 –Mean age yrs; 92% Caucasian; 46% female; 37% had income >$70,000 Assessed knowledge, satisfaction, information needs, resources, & health perception –Quantitative and qualitative methods J Thromb Haemost 2003; 1:2335

Individuals with Factor V Leiden Mutation Knowledge –39% did not recall giving consent –10% did not know they were tested –13% did not know that they carried the mutations –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

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

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

Implications for Future Patients interested in genetic testing for any condition need genetic counseling: –Genetic and environmental risk factors –Disclosure –Meaning of test results –Other risks/benefits –Follow-up

References American College of Medical Genetics Consensus Statement on Factor V Leiden Mutation Testing. Genet Med 2001; 3: 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.

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

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

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: 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: