By age 16, close to 2 children in 3 have suffered at least one adverse experience such as parental death, life-threatening illness, or family violence. Adversities have been robustly linked to psychiatric and other medical conditions where the consequences can persist far into adulthood. It is not well understood how early adverse experiences are biologically embedded and what processes might be set into effect that would sustain long term health risks. To address these key questions we performed a prospective, longitudinal methylome-wide association study (MWAS) of childhood adversity where data on adverse experiences was linked to methylation data on almost all 28 million common methylation sites in blood. Specifically, we used samples from the Great Smoky Mountains Study (GSMS). The GSMS started at Duke University about 25 years ago when participants were 9- to 13-year-old and continues today as the participants are in their 30s. The methylome was assayed using and optimized lab protocol for methyl-CG binding domain sequencing (MBD-seq).
Results showed that childhood adversity has a substantial impact on the methylome. These effects tended to increase with the number of adverse events and were predictive of future health outcomes. For example, using k-fold cross validation to obtain an unbiased estimate of the effects size, lifetime cumulative adversity exposure shared over 20% of its variation with the methylome. This adversity associated methylation variation in childhood (14.2 years of age) was a better predictor of depression symptoms in adulthood (25.8 years of age) then childhood depression symptoms themselves and this contribution remained significant after regressing out the cumulative adversity exposure count. Cell type specific MWAS suggested that most of the methylation changes involved the granulocyte cell subpopulation.
As a next step we propose to replicate findings in samples from the Avon Longitudinal Study of Children and Parents (ALSPAC). The ALSPAC study is critical for this purpose as, similar to GSMS, samples are available before and after adversity and where adversity induced changes can be linked to an array of health outcomes later in life. Furthermore, as ALSPAC is also a prospective, longitudinal it allows us to create a cumulative (life time) measure of exposure to adversity. As the vast majority of our top findings are not assayed by Illumina methylation array that cover only 450,000 sites (~2% of all common methylation sites in blood), we propose a targeted replication study using a protocol for amplicon sequencing of bisulfite converted DNA that we have already optimized and tested.
Successful completion of this project implies that we gained insight into how childhood adversities alters the methylome and what changes persist over time. We will also have identified processes associated with health risks in childhood/adulthood and found replicable methylation biomarkers associated with these risks. Methylation markers are stable and can be measured cost-effectively in blood, which is relatively easy to collect. Our findings therefore also have translational potential as, for example, diagnostic “biomarkers of health risk“.