bioRxiv2023
BackgroundAdverse early-life experiences (ELA), including poverty, trauma and neglect, affect a majority of the worlds children. Whereas the impact of ELA on cognitive and emotional health throughout the lifespan is well-established, it is not clear how distinct types of ELA influence child development, and there are no tools to predict for an individual child their vulnerability or resilience to the consequences of ELAs. Epigenetic markers including DNA-methylation profiles of peripheral cells may encode ELA and provide a predictive outcome marker. However, the rapid dynamic changes in DNA methylation in childhood and the inter-individual variance of the human genome pose barriers to identifying profiles predicting outcomes of ELA exposure. Here, we examined the relation of several dimensions of ELA to changes of DNA methylation, using a longitudinal within-subject design and a high threshold for methylation changes in the hope of mitigating the above challenges. MethodsWe analyzed DNA methylation in buccal swab samples collected twice for each of 110 infants: neonatally and at 12 months. We identified CpGs differentially methylated across time, calculated methylation changes for each child, and determined whether several indicators of ELA associated with changes of DNA methylation for individual infants. We then correlated select dimensions of ELA with methylation changes as well as with measures of executive function at age 5 years. We examined for sex differences, and derived a sex-dependent impact score based on sites that most contributed to the methylation changes. FindingsSetting a high threshold for methylation changes, we discovered that changes in methylation between two samples of an individual child reflected age-related trends towards augmented methylation, and also correlated with executive function years later. Among the tested factors and ELA dimensions, including income to needs ratios, maternal sensitivity, body mass index and sex, unpredictability of parental and household signals was the strongest predictor of executive function. In girls, an interaction was observed between a measure of high early-life unpredictability and methylation changes, in presaging executive function. InterpretationThese findings establish longitudinal, within-subject changes in methylation profiles as a signature of some types of ELA in an individual child. Notably, such changes are detectable beyond the age-associated DNA methylation dynamics. Future studies are required to determine if the methylation profile changes identified here provide a predictive marker of vulnerabilities to poorer cognitive and emotional outcomes. FundingSupported by NIH P50 MH096889, a Precision Medicine Initiative grant from the State of California (OPR20141) and the Bren Foundation. Research in contextO_ST_ABSEvidence before this studyC_ST_ABSIdentification of individuals at risk for cognitive and emotional problems is required for targeted interventions. At the population level, experiencing early-life adversity has been consistently linked to an elevated susceptibility to various mental illnesses. However, recent studies have revealed a significant limitation in the ability of early-life adversity to predict individual-level risk, and there is presently no reliable tool available to determine whether a child experiencing adversity will develop future mental health problems. Promising efforts to discover predictive markers by examining DNA methylation in peripheral cells are challenged by extensive genetic and epigenetic population variability and the rapid methylation changes taking place during childhood, rendering the identification of clinically valuable predictive markers a complex endeavor. Added value of this studyThis study examined neurodevelopmental outcomes following several dimensions of ELA, including a recently identified dimension-unpredictability of parental and environmental signals to the child. It demonstrates changes in DNA methylation in children exposed to a spectrum of ELA dimensions and severity using alternative approaches to those used previously: It employs a longitudinal within-subject design, enabling assessment of DNA changes within an individual over time rather than a cross section comparison of different groups, and focuses on the first year of life, an understudied epoch of development. The study uses reduced representation bisulfite sequencing to measure methylation, an approach compromising between targeted sequencing and a whole genome approach, and sets a high threshold for methylation changes, in consideration of the large changes of DNA methylation during childhood. Finally, in accord with emerging discoveries of the differential effects of ELA on males and females, the study uncovers sex-effects arising already before puberty. Implications of all the available evidenceCollectively, our study, together with a robust existing literature (1) identifies early-life unpredictability as an additional determinant of DNA methylation changes, (2) indicates that within-subject changes in methylation profiles of peripheral cells hold promise as precision medicine tools for predicting risk and resilience to the adverse consequences of early-life hardships on mental health, and (3) suggests that sex-differences should be explored even prior to puberty. Our study contributes significantly to the important goal of early identification of predictive "epigenetic scars" caused by adverse early-life experiences. Such markers are required for targeting interventions to those most at need.