Does prenatal alcohol exposure affect neurodevelopment? Attempts to give causal answers

Transcription

1 Does prenatal alcohol exposure affect neurodevelopment? Attempts to give causal answers Luisa Zuccolo MRC IEU, School of Social and Community Medicine

2 Background Prenatal alcohol exposure and neurodevelopment Heavy drinking causes FAS and FASD Moderate maternal drinking even suggested protective Safe threshold? Mixed messages Need for causal analyses and elucidation of pathways 2

3 NICE guidelines 2008 DoH (CMO advice) 2012 As a general rule, pregnant women or women trying to conceive should avoid drinking alcohol. If they do choose to drink, to protect the baby they should not drink more than 1 to 2 units of alcohol once or twice a week and should not get drunk. Advice on e.g. containers of alcohol: "Avoid alcohol while pregnant or trying to conceive 3

4 Alcohol use in women of reproductive age - US Behavioural Risk Factors Surveillance System US Binge drinking: 5+ drinks/occasion in past 30 days

5 5 13 December 2013

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7 Odds ratios for total difficulties by mother s drinking category among boys, fully adjusted Residual confounding? 0 Never Not in pregnancy Light Moderate Heavy/Binge Kelly Y et al. J Epidemiol Community Health (2010)

8 Strengthening causal inference Different alcoholic beverages Family-based studies Mendelian randomization Elucidating pathways DNA methylation Refined phenotype: brain scans

9 Effects of different alcoholic beverages: Comparing equally plausible associations 9

10 Child academic achievement Vs maternal alcohol use in pregnancy von Hinke Kessler Scholder S, Wehby G, Lewis SJ and Zuccolo L (under review)

11 Characteristics of parents by maternal beverage preference Consuming wine Older (m) better educated (m+f) higher social class (m) higher income (f) employed (m+f) Consuming beer Smoking (m) lower educated (m+f) worse mental health (m) Single (m) von Hinke Kessler Scholder S, Wehby G, Lewis SJ and Zuccolo L (under review)

12 Maternal Vs paternal effects: Comparing plausible versus implausible associations 12

13 Mothers and fathers smoking on offspring bwt a. Crude Mothers smoking Fathers smoking b. Mutually adjusted Davey Smith G. Basic Clin Pharmacol Toxicol :

14 Maternal Vs paternal effects: head circumference at birth Feature of FAS, linked to brain volume and cognition 14

15 Sample Norwegian Mother and Child cohort (MoBa) Recruited N ~ 110,000 pregnancies, 90,000 mothers + 75,000 fathers Q.aire at 17 week, 32 week gestation Alcohol use assessed before and during each trimester of pregnancy Birth anthropometry from linkage with Medical Birth Registry

16 Maternal-paternal comparisons Maternal alcohol Paternal alcohol Genes Lifestyle / Parenting Gametes Fetal development Genes Lifestyle / Parenting Child development 16

17 Common confounding structure? Main assumption : similar shared gene and shared environment 70-90% heritability (shared genes)* and shared environment component Confounders-alcohol associations were similar for mothers and fathers (direction and size) More so before than during pregnancy U-shaped socio-economic patterning of alcohol intake More marked for maternal alcohol intake More marked for before pregnancy drinking *Taal HR, St Pourcain B, Thiering E, et al. Nat Genet Apr 15;44(5):532-8

18 Distribution of alcohol drinking before pregnancy (usual dose per occasion) 40.00% 35.00% 30.00% 25.00% 20.00% 15.00% mothers fathers 10.00% 5.00% 0.00% No alcohol <1 unit 1-2 units 3-4 units 5+ units Zuccolo L et al. unpublished

19 Distribution of alcohol drinking in pregnancy (usual dose per occasion) 90.00% 80.00% 70.00% 60.00% 50.00% 40.00% mothers fathers 30.00% 20.00% 10.00% 0.00% No alcohol <1 unit 1+ unit Zuccolo L et al. unpublished

20 OR of very small HC for gestational age and alcohol intake ref cat: no alcohol OR Small HC for gestational age OR Small HC for gestational age before pregnancy 1 st trimester pregnancy Mothers Fathers 2 Mothers Fathers <1 unit 1-2 units 3-4 units 5+ units 0 <1 unit 1-2 units 3-4 units 5+ units Zuccolo L et al. unpublished 20

21 Mendelian randomization : Minimising confounding

22 Effect Size Allele frequency and disease susceptibility rare, monogenic ( linkage ) common, complex ( association ) McCarthy et al., 2008

23 Problems of observational epidemiology can be overcome Confounding Independent assortment Reverse causation Biological Due to reporting bias Fixed at conception Measurement error Can be measured (genotyped)

24 MR Vs RCT

25 Instrumental variable analysis G genetic instrument (for X, modifiable exposure) if: 1. G not (independent of) X; 2. G U; 3. Y G (X,U).

26 Using maternal ADH1B as an instrumental variable for maternal alcohol intake Exogenous factor related to exposure but not related to outcomes except through association with exposure

27 Alcohol metabolism

28 Women carrying rare ADH1B allele tend to drink less prior to recognition of pregnancy % 45.0% 40.0% 35.0% 30.0% 25.0% 20.0% common rare 15.0% 10.0% 5.0% 0.0% never < 1 per day 1-6 per week 1+ per day Zuccolo L et al. Hum. Mol. Genet. 2009;18:

29 Odds Ratio Women carrying rare ADH1B allele tend to quit alcohol and not binge drink in pregnancy quitting Vs not in 1st trimester no binge drinking in pregnancy 0.5 Zuccolo L et al. Hum. Mol. Genet. 2009;18:

30 Unconfounded genes, confounded alcohol Observed to expected* number of statistically significant associations (300+ tests) ADH1B and potential confounders p=0.46 (at 5%), p=0.48 (at 1%) But self-reported alcohol associated with most confounders! von Hinke Kessler Scholder S, Wehby G, Lewis SJ and Zuccolo L (under review)

31 Alcohol use in pregnancy and background characteristics von Hinke Kessler Scholder S, Wehby G, Lewis SJ and Zuccolo L (under review) 31

32 Mendelian Randomization 32

33 Difference in KS2 score per increasing category of maternal drinking in pregnancy 33 Analysis Eff. Est. (95% CI) P-value OLS unadjusted 1.4 (1.1, 1.6) < OLS adjusted 0.4 (0.1, 0.6) MR: non-carriers (drink +) Vs carriers (drink -) -1.7 (-3, -0.4) Zuccolo L, Lewis SL, Davey Smith G, et al IJE 2013; 42(5):

34 Association of variation at 10 SNPs in ADH and alcohol drinking (additive model) 34 Zuccolo L et al. Hum. Mol. Genet. 2009;18: The Author Published by Oxford University Press

35 Offspring ADH genotypes as proxies for prenatal alcohol exposure Exogenous factor related to exposure but not related to outcomes except through association with exposure

36 -log(p) Maternal and offspring genotype effects on WISC IQ - unadjusted ADH4 ADH1A ADH1B ADH Mother Offspring Lewis SJ, Zuccolo L, Davey Smith et al PLOS One 2012;7(11):e49407

37 IQ Change ADH risk allele score in offspring and offspring IQ, stratified by maternal alcohol intake in pregnancy All women N=4,167 0 units/wk N=1, units/wk N=2,792-4 P value for interaction (risk allele score X drinking during pregnancy) = Lewis SJ, Zuccolo L, Davey Smith et al PLOS One 2012;7(11):e49407

38 Elucidating pathways

39 Ongoing work Prenatal alcohol exposure 1 Epigenetic effects 2 - DNA methylation Neurodevelopment

40 DNA methylation Mostly unmethylated Gene can be expressed Mostly methylated Reduced or no expression DNA methylation common at CpG sites in the genome

41 DNA methylation and prenatal alcohol exposure Moderate levels of exposure Early gestation comparable to before pregnancy recognition in humans

42 2-step Mendelian randomization 1 2 neurodevelopment neurodevelopment Adapted from: Relton and Davey Smith 2012 IJE

43 Future work ~ 7500 individuals with MRI scans ALSPAC + Saguenay Youth Study (15-17y), Generation R (<10y) Different ages before and after starting alcohol career Different prevalences and correlates of pregnancy drinking GWAS and EWAS on all Cognitive /behavioural outcomes

44 Conclusion - 1 Confusion on effects of moderate drinking in pregnancy as conventional observational epidemiology studies suggest no neurodevelopmental effect or even protection Alternative study designs reveal extensive potential for confounding (eg alcohol from wine Vs alcohol from beer) Maternal and offspring variants in alcohol metabolising genes predict cognitive outcomes in childhood (age 8-11) Offspring genotype effect (maternal genotype adjusted) only in exposed - evidence for causal association of alcohol with IQ (small) Harmful effect of even small amount of alcohol in pregnancy on child s cognition

45 Conclusion - 2 Replication of MR results underway (different cohorts and different SNPs) Other aspects of FASD being studied (eg HC) show little role for maternal but an association with paternal drinking before conception Ongoing and future work centred on elucidating pathways, 1) by studying causal mediating role of DNA methylation, and 2) by using refined phenotypes of brain development (structural MRI)

46 Acknowledgements George Davey Smith Caroline Relton Stephanie von Hinke Kessler Scholder Sarah Lewis Ron Gray Camilla Stoltenberg Per Magnus MRC IEU Bristol NIPH Oslo MRC Population Health Scientist fellowship

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