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

Hereditary Equine Regional Dermal Asthenia homozygote adult working horse with mild signs - A Case Report

Hereditary Equine Regional Dermal Asthenia (HERDA) is an autosomal recessive condition present in the American Quarter Horse and other related breeds. Resulting from a mutation in the peptidyl-prolyl cis-trans isomerase B (PPIB) gene, HERDA is homologous to Ehlers-Danlos syndrome in humans. Characterized by fragile, hyperelastic, skin, HERDA affected horses often present first with slow-healing wounds usually on the dorsum, and resulting in atrophic scars, seromas, and ulcers. As there is no treatment for the condition affected horses are typically reported to be unrideable, and if persistent wounds are sufficiently severe, may require euthanasia. This case report describes clinical presentation and genetic diagnostics of HERDA in an 8-year-old horse with notably mild clinical signs, previously undiagnosed. On recommendation from the referring veterinarian, the horse owners pursued genetic diagnostics for HERDA following development of painful dorsal skin lesions under the saddle area during a riding clinic. The individual was confirmed homozygous for HERDA c.115G>A missense mutation in the PPIB gene by commercial testing service (Etalon Diagnostics Inc.). Further objective studies on the severity and clinical presentation of HERDA are necessary to evaluate complex elements of this disease. Furthermore, mildly affected individuals may be underdiagnosed as a result of not demonstrating the clinical signs that commonly encourage genetic testing.

Biomechanical Effects of Unidirectional Expansion Using Anisotropic Expanders in Horse Skin Tissue

The use of a self-inflating tissue expander is a technique to stretch cutaneous tissues for potential use in reconstructive skin surgeries. This study investigates the mechanical properties of horse skin stretched by the subcutaneous implantation of anisotropic tissue expanders at the forehead, right shoulder, and dorsomedial part of the cannon region of the right forelimb in six (n = 6) horses. After 14 days of skin expansion, expanded and normal (control) skin samples were harvested and their mechanical properties of elastic modulus (EM), maximum force (MF), maximum stress (MSs) and maximum strain (MSr) were evaluated using uniaxial tension test. The expanded skin from shoulder area has higher EM, MSs, MSr and MF than the normal skin when compared to the forehead and lower forelimb. Statistically, there was a significant (P= .02) mean difference for MSs between the expanded shoulder and lower forelimb skin, but the pairwise comparison of EM, MSr and MF showed no significant difference between the locations. The overall effect of locations on EM and MSs was statistically significant (P < .05), however, there was no overall effect of horse factor, treatment factor (normal and expanded skin) and location interaction on the EM, MSS, MF and MSr. In conclusion, the expanded skin from the frontal head and the distal limb are less elastic (stiffer) compared to that of the expanded skin of the shoulder, thus anatomical location of the skin has some degree of effect on EM and MSs.

Distribution of the Warmblood Fragile Foal Syndrome Type 1 Mutation (PLOD1 c.2032G>A) in Different Horse Breeds from Europe and the United States

Warmblood fragile foal syndrome (WFFS) is an autosomal recessive disorder caused by a single nucleotide variant in the procollagen-lysine-2-oxoglutarate-5-dioxygenase 1 gene (PLOD1:c.2032G>A, p.Gly678Arg). Homozygosity for the PLOD1 variant causes an Ehler-Danlos-like syndrome, which has to date only been reported in warmblood breeds but the WFFS allele has been also detected in the Thoroughbred. To investigate the breed distribution of the WFFS allele, 4081 horses belonging to 38 different breeds were screened. In total, 4.9% of the horses representing 21 breeds carried the WFFS allele. The affected breeds were mainly warmbloods, with carrier frequency as high as 17% in the Hanoverian and Danish Warmblood. The WFFS allele was not detected in most non-warmblood breeds. Exceptions include WFFS carriers in the Thoroughbred (17/716), Haflinger (2/48), American Sport Pony (1/12), and Knabstrupper (3/46). The origin of the WFFS allele remains unknown. The Arabian breed and specifically the stallion Bairactar Or. Ar. (1813), whose offspring were reported to have a similar phenotype in the 19th century, were hypothesized as the origin. DNA from a museum sample of Bairactar Or. Ar. showed that he did not carry the mutated allele. This result, together with the genotypes of 302 Arabians, all homozygous for the reference allele, does not support an Arabian origin of the WFFS allele. Our extensive survey shows the WFFS allele to be of moderate frequency and concern in warmbloods and also in breeds where it may not be expected.

A 2-Year-Old Filly With Hereditary Equine Regional Dermal Asthenia: The First Case Report From China

Hereditary equine regional dermal asthenia (HERDA) is an autosomal recessive inheritable disorder described in the Quarter Horses and related breeds. In this case report, a 2-year-old Quarter Horse filly was diagnosed with HERDA based on clinical findings and genetic testing. The observed clinical signs were stretchy, loose and thin skin, and open wounds on the upper body. Skin biopsy results were consistent with the common findings previously described in the literature. This is the first HERDA case report in China (and in Asia). Genetic testing protocols should be implemented for breeding farms to prevent the disease.

Biomechanical and biochemical properties of the thoracic aorta in warmblood horses, Friesian horses, and Friesians with aortic rupture

Background

Thoracic aortic rupture and aortopulmonary fistulation are rare conditions in horses. It mainly affects Friesian horses. Intrinsic differences in biomechanical properties of the aortic wall might predispose this breed. The biomechanical and biochemical properties of the thoracic aorta were characterized in warmblood horses, unaffected Friesian horses and Friesians with aortic rupture in an attempt to unravel the underlying pathogenesis of aortic rupture in Friesian horses. Samples of the thoracic aorta at the ligamentum arteriosum (LA), mid thoracic aorta (T1) and distal thoracic aorta (T2) were obtained from Friesian horses with aortic rupture (A), nonaffected Friesian (NA) and warmblood horses (WB). The biomechanical properties of these samples were determined using uniaxial tensile and rupture assays. The percentages of collagen and elastin (mg/mg dry weight) were quantified.

Results

Data revealed no significant biomechanical nor biochemical differences among the different groups of horses. The distal thoracic aorta displayed an increased stiffness associated with a higher collagen percentage in this area and a higher load-bearing capacity compared to the more proximal segments.

Conclusions

Our findings match reported findings in other animal species. Study results did not provide evidence that the predisposition of the Friesian horse breed for aortic rupture can be attributed to altered biomechanical properties of the aortic wall.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-015-0597-0) contains supplementary material, which is available to authorized users.

Increased susceptibility of skin from HERDA (Hereditary Equine Regional Dermal Asthenia)-affected horses to bacterial collagenase degradation: a potential contributing factor to the clinical signs of HERDA

BACKGROUND

Hereditary equine regional dermal asthenia (HERDA) is a genetic disorder of collagen resulting in fragile, hyper-extensible skin and ulcerative lesions. The predominance of skin lesions have been shown to occur on the dorsum of HERDA-affected horses. While this has been postulated to be due to increased exposure to sunlight of these areas, the precise pathological mechanism which causes this to occur is unclear.

HYPOTHESIS/OBJECTIVES

We hypothesized that an increase in collagenase activity, that has been associated with the exposure of dermal fibroblasts to sunlight, will significantly degrade the material properties of skin from HERDA-affected horses when compared to unaffected controls.

ANIMALS

Six unaffected and seven HERDA-affected horses, all euthanized for other reasons.

METHODS

Full-thickness skin samples from similar locations on each horse were collected and cut into uniform strips and their material properties (tensile modulus) determined by mechanical testing before (n = 12 samples/horse) or after (n = 12 samples/horse) incubation in bacterial collagenase at 37°C for 6 h. The change in modulus following treatment was then compared between HERDA-affected and unaffected horses using a Student's t-test.

RESULTS

The modulus of skin from HERDA-affected horses decreased significantly more than that from unaffected horses following collagenase treatment (54 ± 7% versus 30 ± 16%, P = 0.004).

CONCLUSIONS AND CLINICAL IMPORTANCE

The significant decrease in the modulus of skin from HERDA-affected horses following collagenase exposure suggests that their altered collagen microarchitecture is more susceptible to enzymatic degradation and may explain the localization of skin lesions in HERDA-affected horses to those areas of the body most exposed to sunlight. These findings appear to support the previously reported benefits of sunlight restriction in HERDA-affected horses.

Skin malformations in a neonatal foal tested homozygous positive for Warmblood Fragile Foal Syndrome

Background

Skin malformations that resembled manifestations of Ehlers-Danlos-Syndrome were described in a variety of domestic animals during the last century as cutis hyperelastica, hyperelastosis cutis, dermatosparaxis, dermal/collagen dysplasia, dermal/cutaneous asthenia or Ehlers-Danlos-like syndrome/s. In 2007, the mutation responsible for Hereditary Equine Regional Dermal Asthenia (HERDA) in Quarter Horses was discovered. Several case reports are available for similar malformations in other breeds than Quarter Horses (Draught Horses, Arabians, and Thoroughbreds) including four case reports for Warmblood horses. Since 2013, a genetic test for the Warmblood Fragile Foal Syndrome Type 1 (WFFS), interrogating the causative point mutation in the equine procollagen-lysine, 2-oxoglutarate 5-dioxygenase 1 (PLOD1, or lysyl hydroxylase 1) gene, has become available. Only limited data are available on the occurrence rate and clinical characteristics of this newly detected genetic disease in horses. In humans mutations in this gene are associated with Ehlers-Danlos Syndrome Type VI (kyphoscoliotic form).

Case presentation

This is the first report describing the clinical and histopathological findings in a foal confirmed to be homozygous positive for WFFS. The Warmblood filly was born with very thin, friable skin, skin lesions on the legs and the head, and an open abdomen. These abnormalities required euthanasia just after delivery. Histologic examination revealed abnormally thin dermis, markedly reduced amounts of dermal collagen bundles, with loosely orientation and abnormally large spaces between deep dermal fibers.

Conclusion

WFFS is a novel genetic disease in horses and should be considered in cases of abortion, stillbirth, skin lesions and malformations of the skin in neonatal foals. Genetic testing of suspicious cases will contribute to evaluate the frequency of occurrence of clinical WFFS cases and its relevance for the horse population.

Dermatological and morphological findings in quarter horses with hereditary equine regional dermal asthenia

BACKGROUND

Hereditary equine regional dermal asthenia (HERDA) is an autosomal recessive disorder affecting quarter horses (QHs); affected horses exhibit characteristic skin abnormalities related to abnormal collagen biosynthesis.

HYPOTHESIS/OBJECTIVES

To characterize the thickness and morphological abnormalities of the skin of HERDA-affected horses and to determine the interobserver agreement and the diagnostic accuracy of histopathological examination of skin biopsies from horses with HERDA.

ANIMALS

Six affected QHs, confirmed by DNA testing, from a research herd and five unaffected QHs from a stud farm.

METHODS

The skin thickness in 25 distinct body regions was measured on both sides in all affected and unaffected horses. Histopathological and ultrastructural evaluation of skin biopsies was performed.

RESULTS

The average skin thickness in all of the evaluated regions was thinner in the affected horses. A statistically significant difference between skin thickness of the affected and unaffected animals was observed only when the average magnitude of difference was ≥38.7% (P = 0.038). The interobserver agreement for the histopathological evaluation was fair to substantial. The histopathological sensitivity for the diagnosis of HERDA was dependent on the evaluator and ranged from 73 to 88%, whereas the specificity was affected by the region sampled and ranged from 35 to 75%.

CONCLUSIONS AND CLINICAL IMPORTANCE

Despite the regional pattern of the cutaneous signs, skin with decreased thickness was not regionally distributed in the HERDA-affected horses. Histopathological evaluation is informative but not conclusive for establishing the diagnosis. Samples of skin from the neck, croup or back are useful for diagnosis of HERDA. However, the final diagnosis must be confirmed using molecular testing.