Although autism spectrum disorder (ASD) has been reported to be among the most heritable of neurodevelopmental disorders based on concordance rates among identical twins and siblings, the rapidly rising prevalence of autism in the United States and worldwide suggests that environmental factors may also contribute significantly to ASD. These as yet undefined environmental factors may impact the expression of genes associated with autism through gene by environment (GxE) interactions leading to an autism phenotype, or by modification of the germline epigenome which in turn can lead to transgenerational inheritance of autism. The proposed study directly addresses environmental risk for autism that may arise from epigenetic modifications in human germline cells as a result of exposure to a specific class of endocrine disrupting compounds (EDCs), the organochlorines. In the proposed study, we will test the hypotheses that: 1) environmental exposure to endocrine disrupting organochlorine compounds, which have long half-lives in the environment and bodily tissues, is associated with epigenetic modifications in human sperm cells that affect autism risk genes, identified through bioinformatics analyses of the methylomic data, 2) that the expression and epigenetic regulation of genes mapped to differentially methylated regions (DMRs) are altered by the specific EDCs in a neuronal cell model.
Specific Aims are: 1) conduct large-scale, genome-wide DNA methylation analyses of sperm from men with known exposure levels to different EDCs, as quantified in their serum; 2) perform bioinformatics and pathway analyses of the differentially methylated regions/genes to determine the relationship to genes and pathways implicated in autism; 3) validate differential methylation associated with key ASD-related genes that correlate with high levels of exposure to specific EDCs in the respective serum samples; 4) use a neuronal cell model to directly test the ability of specific EDCs to alter gene expression and methylation of ?ASD-driver? genes found to be differentially methylated in sperm. Impact: This study is particularly compelling given recent findings of altered DNA methylation in the sperm of a cohort of fathers of children with elevated risk for autism. We anticipate that this study will show that EDCs are a significant environmental risk factor for ASD that may increase susceptibility by modifying the sperm epigenome, thereby causing dysregulation of specific autism risk genes critical to neurological development and function. Moreover, establishment of a database of EDC-associated changes in the sperm methylome is expected to be a valuable resource for studies on other diseases/conditions, such as cancer, obesity, diabetes and infertility, which are linked to environmental exposures. Innovation: This study will be the first to investigate the relationship between quantified EDC exposures and epigenomic changes to human sperm DNA, with a particular focus on genes/pathways implicated in autism. These studies will fill a gap in our knowledge of environmentally-induced epigenetic changes in human germline cells in relation to increased risk for ASD. Since epigenetic modifications in the germline may be transmitted transgenerationally, such changes may contribute to the ?missing heritability? in ASD.
Although autism appears to be strongly inherited based on the fact that identical twins have a high probability of both being affected by the disorder, there is still a component of autism risk that cannot be explained simply by genetic factors. Recently, there has been increasing awareness and appreciation for potential environmental contributors to autism. This study will be the first to investigate epigenetic modifications in human sperm DNA (that do not cause changes in DNA sequence) that associate with environmental exposure to a specific group of chemicals (bioavailable endocrine disruptors), with a particular focus on identifying changes that affect genes that may increase risk for autism.
