A Genetic Basis for Adhesive Capsulitis?

This post comes from Fred Nelson, MD, an orthopaedic surgeon in the Department of Orthopedics at Henry Ford Hospital and a clinical associate professor at Wayne State Medical School. Some of Dr. Nelson’s tips go out weekly to more than 3,000 members of the Orthopaedic Research Society (ORS), and all are distributed to more than 30 orthopaedic residency programs. Those not sent to the ORS are periodically reposted in OrthoBuzz with the permission of Dr. Nelson.

Adhesive capsulitis (AC), colloquially known as frozen shoulder, is associated with conditions such as diabetes, cardiopulmonary disorders, stroke, Parkinsonism, and injury. However, many cases are idiopathic. Given the inflammatory nature of the condition, clinicians often administer intra-articular steroid injections in recalcitrant cases where physical therapy alone is too painful or nonproductive. Some cases, particularly in patients with diabetes, may require manipulation, brisement, or arthroscopic release.

To better understand the genetic basis of AC, investigators obtained punch tissue samples from the middle glenohumeral ligament and rotator cuff interval from AC patients undergoing arthroscopic release surgery (mean age of 53 years) and from a comparative group of patients undergoing arthroscopic surgery for shoulder instability (mean age of 24 years).¹ The researchers performed RNA sequencing-based transcriptomics on the samples and, after identifying differentially expressed genes, they applied real-time reverse transcription polymerase chain reaction (RT-PCR) to obtain more detailed genetic data.

A total of 545 genes were differentially expressed. The top 50 were associated with extracellular matrix remodeling. Patient age and sex did not have a major influence on gene expression. The genes marked by overexpression (not necessarily protein expression) were genes for matrix metallopeptidase 13 and platelet-derived growth factor subunit B. Other suspects included the gene for metalloprotease 9 and COL18A1.

In the discussion, the authors comment on the association between AC and protein tyrosine kinase 2 (PTK2), also known as focal adhesion kinase (FAK). FAK activation is particularly sensitive to fibronectin and other integrins. Activated FAK also controls cell migration and focal adhesion assembly. These interesting associations may also shine light onto the etiology of other musculoskeletal diseases.

Reference

1. Kamal N, McGee SL, Eng K, Brown G, Beattie S, Collier F, Gill S, Page RS.
   Transcriptomic analysis of adhesive capsulitis of the shoulder. J Orthop Res. 2020 Oct;38(10):2280-2289. doi: 10.1002/jor.24686. Epub 2020 Apr 17. PMID: 32270543