Can Autoimmunity Against Calsequestrin Explain the Eye and Eyelid Muscle Inflammation of Thyroid Eye Disease?

Extra-ocular and upper eyelid (levator) muscle damage in thyroid orbitopathy may be due to autoimmunity against eye muscle auto antigens. The main antigen appears to be the calcium binding protein calsequestrin. In this study we have tested for T lymphocyte sensitization to calsequestrin in patients with Graves' disease, with and without orbitopathy, in standard proliferation assay. We have also tested total RNA prepared from thyroid tissue of patients with Graves' disease with and without orbitopathy for expression across 20,589 genes using micro array analysis technology. We were looking for differences in gene expression between the two groups which might provide information about the early thyroid events that lead to the development of eye muscle autoimmunity. Positive lymphocyte reactivity to calsequestrin was demonstrated in 59% of Graves' patients with orbitopathy, 33% without evident ophthalmopathy and in 43% of patients with Hashimoto's thyroiditis and upper eyelid retraction (UER). Two hundred and ninety six genes were identified to be differentially expressed between in patients with Graves' disease with and without orbitopathy. Of these, the cardiac calsequestrin gene CASQ2 was the most highly up regulated, 2.2-fold. The closely related skeletal muscle calsequestrin gene CASQ1 was also up-regulated, 4.1 fold, but this was not significant, while genes encoding the thyroid antigens thyroglobulin, thyroid peroxidase and the TSH-receptor were not differentially expressed. These findings provide further evidence for a prominent role of autoimmunity against calsequestrin in the pathogenesis of the eye muscle components of thyroid orbitopathy.