Constitutively low expression of collagen XIII alpha 1 may help explain the vulnerability of the inferior rectus muscle to thyroid-associated ophthalmopathy

ABSTRACT

Thyroid-associated ophthalmopathy (TAO) has a predilection for inferior rectus muscle that has never been explained. We conducted immunohistochemical staining for the soluble cleaved form of collagen XIII alpha 1 (COL13A1) and found constitutively low expression of COL13A1 in normal human inferior rectus muscles and moderate expression of COL13A1 in normal human medial rectus muscles. COL13A1 is known to be essential to development and maintenance of neuromuscular junctions and there is some evidence to suggest it may help support normal immune function. The combination of constitutively low expression of COL13A1, high physiological and metabolic demands, and consequentially relatively high exposure to stressors via the blood stream may help explain the particular vulnerability of inferior rectus to TAO compared to other extraocular muscles.

KEYWORDS:

• collagen XIII
• COL13A1
• thyroid-associated ophthalmopathy
• thyroid eye disease

Acknowledgments

We would like to thank all the patients, surgeons and staff at University Geelong Hospital, Barwon Health, Geelong Private Hospital, the Royal Victorian Eye and Hospital, St. Vincent’s Private Hospital, Munich University Eye Hospital, South Munich Eye Centre and the Department of Rheumatology and Inflammation Research, University of Gothenburg, Sweden, who contributed to this work.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article.