MATERNAL INFLUENCES ON OFFSPRING S EPIGENETIC AND LATER BODY COMPOSITION

Institute of Medicine & National Research Council Food and Nutrition Board & Board on Children, Youth & Families Examining a Developmental Approach to Childhood Obesity: The Fetal & Early Childhood Years February 26-27 2015 MATERNAL INFLUENCES ON OFFSPRING S EPIGENETIC AND LATER BODY COMPOSITION Caroline Relton MRC Integrative Epidemiology Unit School of Social & Community Medicine, University of Bristol Institute of Genetic Medicine, Newcastle University

Maternal over- and under-nutrition during pregnancy and childhood adiposity Maternal BMI and gestational weight gain are associated with increased offspring adiposity and other adverse pregnancy outcomes What are the biological mechanisms explaining this link? Lawlor DA, Relton CL, Sattar N, Nelson S. Nat Rev Endocrinol 2012

Understanding whether epigenetic processes are a mediating mechanism linking an exposure and a disease Michels K, Epigenetic Epidemiology Springer 2012 Chapter 3, Study Design

Interpreting observed associations in epigenetic (or other observational) studies Epigenetic marks, (like other potentially causal factors, from molecular biomarkers to behaviours) are vulnerable to confounding and reverse causation Exposure CpG CpG CpG CpG Exposure Exposure Exposure Correlation Cause Reverse cause Confounding

Epigenetics as a potential mechanism mediating maternal influences on childhood body composition Step 1 Establish an association between maternal factors (body weight and weight gain during pregnancy) and offspring adiposity Step 2 Establish a relationship between the same exposure and child s DNA methylation Step 3 Establish an association between child s DNA methylation and child s adiposity Step 4 Apply methods to strengthen causal inference

The Avon Longitudinal Study of Parents and Children (ALSPAC) Antenatal <1y 1y 2y 3y 4y 5y 6y 7y 8y 9y 10y 11y 12y 13y 16+ Child s health (e.g. medical history, anthropometry) Child s demographics (e.g. ethnicity, social background) Environmental health (e.g. pollutant exposure) Child s lifestyle (e.g. physical activity, diet) Child s school & education Child s behaviour and psychology Child s development (e.g. cognitive, motor skills, puberty) Parent s lifestyle (e.g. smoking & drinking) Parent s psychological well-being Biological samples (blood, plasma, serum, cells, tissue, hair, urine) Genome-wide DNA methylation (Illumina Infinium HumanMethylation450 BeadChip) www.bristol.ac.uk/alspac www.ariesepigenomics.org.uk

Maternal pre-pregnancy BMI and gestational weight gain, offspring DNA methylation and later offspring adiposity: Findings from the Avon Longitudinal Study of Parents and Children Gemma Sharp, Debbie A Lawlor, Rebecca C Richmond, Abigail Fraser, Andrew Simpkin, Matthew Suderman, Hashem A Shihab, Tom Gaunt, Oliver Lyttleton, Wendy McArdle, Susan M Ring, George Davey Smith, Caroline L Relton Int J Epidemiol, submitted 2014

Epigenome-wide association study of maternal overand undernutrition on offspring DNA methylation

APPROACHES FOR STRENGTHENING CAUSAL INFERENCE IN EPIGENETIC STUDIES Randomized controlled trials Cross-cohort comparisons Negative controls Parental comparisons Sibling comparisons Appraising temporal relationships through longitudinal analysis Mendelian randomization

Randomized controlled trial Randomized Intervention Exposed: Intervention Confounding equal Control: No intervention Outcome Compare risk of outcome Outcome

Cohort comparison Cohort 1 Exposure Cohort 2 Exposure 1 st set of confounders 2 nd set of confounders Outcome Outcome Compare magnitude of association

Negative control Exposure e.g. Maternal phenotype Exposure e.g. Paternal phenotype Shared confounders Outcome e.g. Offspring phenotype Outcome e.g. Offspring phenotype Compare magnitude of association

Maternal prenatal nutrition and offspring adiposity: An example of the use of negative controls

Sibling control Exposure In 1 st pregnancy No exposure In 2 nd pregnancy No familial confounding Outcome in older sibling Outcome in younger sibling Compare risk of outcome between siblings

Offspring adiposity pre and post maternal bariatric surgery Pediatrics 2006;118;e1644

Longitudinal modelling Confounders Confounders Exposure Intermediate phenotype Outcome BUT a temporal association between exposure and outcome does not necessarily avoid confounding

Longitudinal modelling of DNA methylation patterns

Mendelian randomization Confounders Instrumental Genotype variable Modifiable exposure Outcome

Mendelian randomization applied to epigenetics Confounders Maternal Instrumental BMI allele variable score Maternal BMI Child s DNA methylation Confounders Instrumental Child s cis-meqtl variable Child s DNA methylation Child s BMI

DNA methylation and body mass index: investigating identified methylation sites at HIF3A in a causal framework Rebecca C Richmond, Gemma Sharp, Mary E Ward, Abigail Fraser, Oliver Lyttleton, Wendy McArdle, Susan M Ring, Tom R Gaunt, Debbie A Lawlor, George Davey Smith, Caroline L Relton 1000 ALSPAC mother/offspring pairs Pre-pregnancy BMI BIRTH 7 years 15-17 years HIF3Am cord blood HIF3Am peripheral blood HIF3Am peripheral blood Legend: Cross-sectional association Offspring BMI Offspring BMI Mendelian randomization analysis Longitudinal association Inter-generational association

Confounders Maternal BMI allele score Maternal BMI Child s DNA methylation Evidence that maternal BMI has a causal effect on child s DNA methylation at HIF3a Maternal BMI b c a Methylation at HIF3A in child Maternal BMI allele score Test for difference between the observed and expected estimates, i.e. compare a with b c N = 674

Confounders Instrumental Child s cis-meqtl variable Child s DNA methylation Child s BMI No strong evidence that child s DNA methylation at HIF3a has a causal effect on BMI Methylation at HIF3A in child b c a Child s BMI Cis-SNP allele score Test for difference between the observed and expected estimates, i.e. compare a with b c N = 831

Confounders Child s Instrumental BMI allele variable score Child s BMI Child s DNA methylation Some evidence that child s BMI has a causal effect on DNA methylation at HIF3a Child s BMI b c a Methylation at HIF3A in child BMI allele score Test for difference between the observed and expected estimates, i.e. compare a with b c N = 831

Maternal BMI, HIF3A methylation and offspring adiposity: a Mendelian randomization approach Proposed direction of causality: Maternal BMI Child s DNA methylation at HIF3a Child s BMI Likely direction of causality: Indirect effect through offspring BMI Maternal BMI Child s BMI Child s DNA methylation at HIF3a Direct intra-uterine effect

Epigenetics as a potential mechanism mediating maternal influences on childhood body composition Step 1 Establish an association between maternal factors (body weight and weight gain during pregnancy) and offspring adiposity Step 2 Establish a relationship between the same exposure and child s DNA methylation Step 3 Establish an association between child s DNA methylation and child s adiposity Step 4 Apply methods to strengthen causal inference

Future directions Step 1 Better observational evidence using more refined measures of maternal exposures Step 2 Improved technology for assessment of genome-wide DNA methylation Step 3 Both of the above Step 4 Increased awareness of pitfalls of association studies and approaches for strengthening causal inference; more widespread implementation and encouragement of triangulation of evidence

Acknowledgements Contributors to the work presented: George Davey Smith Abigail Fraser Tom Gaunt Debbie Lawlor Oliver Lyttleton Wendy McArdle Rebecca Richmond Sue Ring Gemma Sharp Andrew Simpkin Matthew Suderman Hash Shihab Mary Ward