Role of genetics and epigenetics in Graves' orbitopathy.

Objectives: The pathogenesis of Graves' orbitopathy (GO) remains to be fully elucidated. Here, we reviewed the role of genetics and epigenetics. Design: We conducted a PubMed search with the following keywords: GO, thyroid eye disease; or Graves' ophthalmopathy; or thyroid-associated ophthalmopathy; and: genetic, or epigenetic, or gene expression, or gene mutation, or gene variant, or gene polymorphism, or DNA methylation, or DNA acetylation. Articles in which whole DNA and/or RNA sequencing, proteome, and methylome analyses were performed were chosen. Results: The different prevalence of GO in the two sexes, as well as racial differences, suggest that genetics play a role in GO pathogenesis. In addition, the long-lasting phenotype of GO and patient-derived orbital fibroblasts suggests a genetic or epigenetic mechanism. Although no genes have been found to confer a specific risk for GO, differential gene expression has been reported in orbital fibroblasts from GO patients vs control fibroblasts, suggesting that an epigenetic mechanism may be involved. In this regard, a different degree of DNA methylation, which affects gene expression, has been found between GO and control fibroblasts, which was confirmed by whole methylome analysis. Histone acetylation and deacetylation, which also affect gene expression, remain to be investigated. Conclusions: Although no pathogenic gene variants have been reported, epigenetic mechanisms elicited by an initial autoimmune insult seem to be needed for differential gene expression to occur and, thus, for GO to develop and persist over time.