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Nickisa Hodgson, Ken Flagg, Cindy Wen, Michal Krawczyk, Emily Yeh, Michael Ai, Bobby Korn, Don Kikkawa, Kang Zhang; Genome Wide Epigenetic Analysis in Thyroid Eye Disease. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5509.
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© ARVO (1962-2015); The Authors (2016-present)
Thyroid eye disease (TED) is a source of significant morbidity in patients with thyroid disease. Features associated with TED include eyelid retraction, proptosis, restrictive myopathy, and optic neuropathy. The Consensus Statement of the European Group on Graves’ Orbitopathy (EUGOGO) on Management of Graves’ Orbitopathy (GO) published a clinical severity classification that categorizes patients into sight-threatening GO (corneal breakdown or optic neuropathy), moderate to severe GO (lid retraction > 2 mm, exophthalmos > 3mm, diplopia, and moderate to severe tissue involvement), and mild GO (lid retraction < 2mm, exophthalmos < 3 mm, no diplopia, and mild tissue involvement). Genome wide association studies have thus far failed to identify major and large effect variants for thyroid disease and TED, suggesting other factors such as epigenetic and environmental influence. Epigenetic variants associated with thyroid and thyroid eye disease have yet to be studied in detail. Alterations in DNA methylation may contribute to the development of TED and the severity of eye disease in patients with thyroid disease.
Whole blood samples were obtained from a total of 45 patients with thyroid eye disease. Samples were processed with the Illumina Infinium HumanMethylation450 Bead Chip assay, which measures the methylation states of 485,577 CpG markers. Methylation data were analyzed as a fraction between zero and one, representing the frequency of methylation of a given CpG marker across the population of blood cells taken from a single individual. Statistical analysis was performed using R. A total of 45 thyroid eye disease subjects were analyzed and categorized according to the EUGOGO classification. Of 45 subjects, nine met criteria for mild GO, 36 were moderate to severe. 485,577 markers were compared between mild and moderate to severe cases using the colttests() function in the R gene filter package.
Methylation of marker cg01423883 was found to have a methylation fraction difference of 5% in mild TED vs moderate to severe TED patients. This difference was significantly associated with thyroid eye disease (P <8.3xE-08). This association remains significant after adjusting for all 485,577 markers (P<0.037).
These results provide evidence that changes in DNA methylation and epigenetic variants have a role in the development of thyroid eye disease and the clinical severity.
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