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 key words: Graves' orbitopathy, 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 analysis 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 of patient-derived orbital fibroblasts suggest 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 pathogenetic gene variants have not 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.