The effect of epigenetic variation on thyroid development and function is an area with limited studies. Initial studies point to an environmental link between PAX8 methylation and thyroid phenotype. Studies have described seasonal variation in the incidence of congenital hypothyroidism and thus it is important to explore epigenetic causes and environmental influence. This study would provide insights into the relationship between PAX8 methylation and thyroid function across a large cohort and specifically in twins. It also provides the opportunity to explore periconceptual environmental factors. By understanding more about the impact of the periconceptual environment and the role of epigenetics in regulating thyroid function we can plan further studies to explore periconceptional interventions (e.g. nutritional) that may limit congenital hypothyroidism, which is especially important for those countries without screening. Understanding more about the epigenetic role in thyroid function would also support further work into the fundamental biology of thyroid regulation. We are liasing with the Costagliola lab in Brussels and the Pediatric Endocrinology Department at Universitatsmedizin, Berlin exploring future research opportunities using stem cells to investigate PAX8 methylation and thyroid function and hope that this research would support these collaborations. Establishing the link between maternal environment, DNA methylation and the impact on the thyroid through this research will provide the basis for a larger grant application for research at both a cellular level and across other datasets. We plan to disseminate our research through publications and conference presentations.