Tensile properties in collagen-rich tissues of Quarter Horses with hereditary equine regional dermal asthenia (HERDA).

This research project investigates the structural abnormalities in specific tissues of Quarter Horses suffering from the genetic disorder known as Hereditary equine regional dermal asthenia (HERDA). The study shows that tissues, such as tendons, ligaments, and large blood vessels which have high collagen content are significantly weaker in these horses compared to those without this genetic mutation.

Background and Objective

• This study revolves around the hereditary disorder in Quarter Horses called Hereditary equine regional dermal asthenia (HERDA). This autosomal recessive disorder is characterized by skin fragility due to a mutation in the peptidyl-prolyl cis-trans isomerase B (PPIB) gene. This mutation changes the method by which fibrillar collagen folds and receives post-translational modifications.
• The purpose of the study was to evaluate whether tissue types other than skin, specifically those with high levels of fibrillar collagen such as tendons, ligaments, and great vessels, also showcase abnormal biomechanical properties in horses with HERDA.

Methods

• The researchers conducted an ex vivo biomechanical study comparing horses diagnosed with HERDA against those without the disorder.
• Samples of the forelimb suspensory ligament, superficial and deep digital flexor tendons, skin from different regions, the main pulmonary artery, and the aortic arch were collected and examined from six horses diagnosed with HERDA and six control horses without HERDA.
• The samples were then subjected to mechanical stress until failure. Mechanical properties like tensile strength (TS), elastic modulus (EM), and energy to failure (ETF) were then compared between the HERDA and non-HERDA groups.

Results

• The horses identified with HERDA showed evidently lower tensile strength and elastic modulus values in tendon, ligament, and great vessel tissues when compared to the control group.
• The skin samples from the horses with HERDA also displayed significantly lower values in regards to tensile strength, elastic modulus, and energy to failure.
• Differences in tensile strength and energy to failure were more notable around the area of the withers in comparison to the forelimb or abdomen.

Conclusion

• The research concludes that tissues rich in fibrillar collagen, such as tendons, ligaments, large blood vessels, and skin are significantly weaker in horses suffering from HERDA in comparison to those that do not possess the PPIB gene mutation.
• Therefore, the study validates the theory that a wide range of tissues with high fibrillar collagen content are abnormal in horses with HERDA and shows that the consequences of the HERDA mutation are not limited only to the skin.