Gene-Environment Interactions Nazarbayev University July 2012 Jan Dorman, PhD University of...
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Transcript of Gene-Environment Interactions Nazarbayev University July 2012 Jan Dorman, PhD University of...
Gene-Environment Interactions
Nazarbayev UniversityJuly 2012
Jan Dorman, PhDUniversity of PittsburghPittsburgh, PA, [email protected]
Evidence of Gene-Environment Interactions
Familial aggregation of disease– Greater prevalence of disease in 1st
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 0.76 0.65
15-29 yrs 3.54 0.40
30-34 yrs 1.35 0.26
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
Strata Cases(Affected)
Controls(Unaffected)
Susceptible & Exposed (S+E+)
a b
Susceptible & Not Exposed (S+E-)
c d
Not Susceptible & Exposed (S-E+)
e f
Not Susceptible & Not Exposed (S-
E-)
g h
Gene-Environment Interactions
Gene-Environment Interactions
Strata Cases Controls
S+E+ a b
S+E- c d
S-E+ e f
S-E- g h
Odds Ratio (OR)
ah / bg
ch / dg
eh / fg
1
Example of Additive Effects
S+E+ 21 7S+E- 15 5S-E+ 9 3S-E- 3 1
66
66
StrataStrata RiskRisk RatioRatioDifference Difference AbsoluteAbsolute OddsOdds
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
Example of Multiplicative Effects
S+E+ 45 15S+E- 15 5S-E+ 9 3S-E- 3 1
33
33
StrataStrata RiskRisk Difference Difference AbsoluteAbsolute
RatioRatio Odds Odds
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
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; 344:1453-1547
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%
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 1st 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
OCP, Factor V Leiden Mutations and Venous ThrombosisStrata Cases Control
sS+E+ 25 2
S+E- 10 4
S-E+ 84 63
S-E- 36 100
OR (95% CI)
34.7 (7.8, 310.0)
6.9 (1,8, 31.8)
3.7 (1.2, 6.3)
Reference
Total 155 169Lancet 1994;344:1453
Additive Effects?
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
Multiplicative Effects?
OR Interaction =
34.7 / 6.9 x 3.7 = 1.4
Strata OR
S+E+ 34.7
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
Strata Number of Cases
Prevalence
Controls
Person Years
Risk/10,000/ yr
S+E+ 25 1.1% 8,800 28.5
S+E- 10 2.4% 17,760 5.7
S-E+ 84 37.3% 276,020 3.0
S-E- 36 59.2% 438,082 0.8
Total 155 100.0% 740,000 2.1
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 41-60 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; 3:139-148.
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.
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.
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.
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.