The impact of social determinants of health on placental CpG methylation and severity of neurodevelopmental burden in children born extremely preterm

BACKGROUND: It has long been accepted that the environment we experience can impact our well-being; throughout recorded history, the greatest prevalence and severity of disease has been experienced by marginalized and underserved populations. However, the translation of such nontangible influences into biological changes in our health has been elusive until the recent advent of epigenetic studies. Modifications outside of the genome play a critical role in regulating transcription as well as subsequent gene expression without altering DNA sequencing by controlling the accessibility of the DNA for interaction with key initiation proteins and enzymes. These modifications, which include DNA methylation, histone acetylation, and small noncoding microRNA regulation, have increasingly been found to have a fluid, adaptive response to experiences throughout life. Based on the literature supporting societal stressors negatively impacting neurologic outcome, as well as elucidating an association between epigenetic changes and adverse neurologic outcome, we hypothesize that alterations in CpG methylation sites associated with socioeconomic adversity will also be correlated with the incidence of Neurodevelopmental Disorders. METHODS: 889 of the 1,506 neonates initially recruited from 14 medical centers throughout the United States at their time of birth qualified to participate in this study. Placental samples were taken immediately following delivery and neonatal blood samples were taken within the first month of life. Children that survived were followed at 2 years old and 10 years old to evaluate for the presence of four possible Neurodevelopmental Disorders: cognitive impairment, Cerebral Palsy, Autism Spectrum Disorder, and epilepsy. Taking this data as well as demographic information into consideration, the entire cohort included in this study was first evaluated for aberrant methylation levels at 33 CpG sites previously associated with socioeconomic adversity to analyze the degree of significant correlation between altered methylation status and Neurodevelopmental Disorder prevalence. A secondary Epigenome-Wide Association Study was conducted for each of our 889 participants to pinpoint significant changes in CpG methylation in order to evaluate the relationship between altered methylation of particular genes and incidence of Neurodevelopmental Disorders. Taking the previous finding that cognitive impairment imposes a greater burden on both the individual and society than non-cognitive impairment into consideration, both analyses were categorized based on this measure of impairment severity: No Impairment, Non-Cognitive Impairment (diagnosed with Cerebral Palsy, Autism Spectrum Disorder, and/or epilepsy without cognitive deficit), and Cognitive Impairment (cognitive deficit with or without other neurodevelopmental disorders present). RESULTS: Primary analysis of the 33 CpG sites previously associated with socioeconomic adversity did not reveal any significant associations with Non-Cognitive or Cognitive Impairment. However, cg15519318 and cg10613063 (located in the PCCB gene) were marginally associated with Non-Cognitive Impairment while cg02765535 (located in the NTN4 gene) was marginally associated with Cognitive Impairment. Secondary analysis of the entire epigenome found 4 CpG sites significantly associated with Non-Cognitive Impairment (cg07322235, cg13592565, cg13723879, and cg24387818) as well as 4 CpG sites significantly associated with Cognitive Impairment (cg23081580, cg14134658, cg00762003, and cg08546514). DISCUSSION: We were not able to define a significant relationship between the CpG methylation sites related to socioeconomic adversity and adverse neurodevelopmental outcomes. This could stem from several causes, including insufficient power as well as limiting our evaluation of the extensive list of environmental influences to the four measures of societal stress focused on in this study (low educational attainment, single relationship status, public health insurance, and receiving supplemental nutrition assistance). Investigating the epigenome for differential methylation that was significantly associated with the incidence of Neurodevelopmental Disorders identified CpGs associated with several important genes, including genes coding for Neuregulin-3 (NRG3) and Premature Ovarian Failure Actin Binding Protein 1B (POF1B) region with Non-Cognitive Impairment as well as genes coding for Six-Transmembrane Epithelial Antigen of Prostate 2 Metalloreductase (STEAP2), Ly1 Antibody Reactive (LYAR), 1-Acylglycerol-3-Phosphate O-Acyltransferase 3 (AGPAT3), and Ninein-like protein (NINL) with Cognitive Impairment