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

Solar radiation leads to increased collagenase gene expression (MMP1) in HERDA (Hereditary equine regional dermal asthenia) affected horses and may explain the typical dorsal distribution of their lesions

BACKGROUND

Hereditary equine regional dermal asthenia (HERDA) is a genetic disease that alters collagen biosynthesis. Affected horses exhibit fragile, hyperextensible skin, especially over the dorsal region. Although ultraviolet (UV) radiation seems to contribute to the regional distribution of lesions and worsening of clinical signs, the molecular mechanisms involved are largely unknown.

OBJECTIVES

To evaluate the effect of solar radiation on matrix metalloproteinase MMP1, MMP8 and MMP13 gene expression in the dorsal and ventral skin of HERDA-affected and HERDA-unaffected horses [wild-type (WT) horses].

ANIMALS

Six HERDA-affected and six unaffected Quarter horses (WT) were paired according to age, sex and coat colour.

MATERIALS AND METHODS

Horses were submitted to 30 day sunlight restriction, followed by 15 day sunlight exposure. Dorsal and ventral skin biopsies were obtained at six sampling times over 45 days. The expression of MMP1, MMP8 and MMP13 genes was measured by quantitative PCR.

RESULTS

Although solar radiation modulated MMP1, MMP8 and MMP13 expression, the effects were more pronounced on MMP1. Sun exposure for three days significantly upregulated MMP1 in the dorsal region when compared to the ventral skin in both unaffected and HERDA-affected horses.

CONCLUSIONS AND CLINICAL RELEVANCE

This study shows that solar irradiation leads to upregulation of skin collagenase genes particularly MMP1 in the dorsal, sun-exposed skin of horses. Furthermore, this was more marked in HERDA-affected horses. The increased activity of collagenases on the disorganised collagen present in HERDA affected horses would explain why UV radiation leads to deterioration of clinical signs in affected individuals.

Prevalence of the Mutations Responsible for Glanzmann Thrombasthenia in Horses in Brazil

Simple Summary

Hereditary bleeding disorders occur in different species due to mutations in genes coding specific hemostatic proteins leading to alterations in their synthesis, or to the production of non-functional proteins which leads to impairment of hemostasis. Some of these disorders have been described in horses, i.e., Von Willebrand disease (VWD), hemophilia A, and Glanzmann’s thrombasthenia (GT). GT is an inherited disease characterized by hemorrhage and has been described in different species including horses of varied breeds (Thoroughbred, Standardbred, Oldenburg, Peruvian Paso, and Quarter Horse). There are two different mutations described in horses a single guanine to cytosine substitution (CGG for CCG) and a 10 base pair deletion in the ITGA2B gene.

Abstract

Glanzmann’s thrombasthenia (GT) is an autosomal recessive inherited disorder characterized by changes in platelet aggregation, leading to hemorrhage and epistaxis. To date, two independent mutations have been described in horses and associated with this disorder, a point mutation (c.122G > C) and a 10-base-pair deletion (g.1456_1466del) in the Integrin subunit alpha2β gene (ITGA2B) of horses of different breeds (Quarter Horse, Thoroughbred, Oldenburg, and Peruvian Paso). ITGA2B codifies the αIIb subunit of the αIIbβ3 integrin, also termed platelet fibrinogen receptor. Horses with GT have been diagnosed in the USA, Canada, Japan, and Australia. However, there are no studies on the prevalence of GT in horses. The aim of this study is to evaluate the prevalence of the mutations responsible for GT in horses in Brazil. A total of 1053 DNA samples of clinically healthy Quarter Horse (n = 679) and Warmblood horses (n = 374) were used. DNA fragments were amplified by PCR and sequenced. The genotype of each animal was analyzed and compared to the nucleotide sequence of the ITGA2B gene found on GenBank^TM. There were no carriers in the analyzed samples, that is, all animals tested were wild type. Therefore, under the conditions in which this study was carried out, it can be inferred that GT seems to be extremely rare in the population of Quarter Horses and Warmbloods in Brazil, although it is not possible to affirm that there are no horses carrying mutated alleles in Brazil.

Evaluation of the Structure of Myodural Bridges in an Equine Model of Ehlers-Danlos Syndromes

Myodural bridges have been described in various species as connective tissue structures “bridging” small cranio-cervical muscles to the dura. Myodural bridges are thought to stabilize the dural sac during head and neck movements and promote cerebrospinal fluid motion; however, their role in neurological diseases has not yet been established. We report ultrasonographic visualization, necropsy, histopathologic and ultrastructural findings of myodural bridges in horses with hereditary equine regional dermal asthenia (HERDA), an equine model of Ehlers-Danlos syndromes. Five HERDA and 5 control horses were studied. Post-mortem examination and ultrasonographic studies (3 HERDA and 4 controls) demonstrated that the atlanto-occipital and atlanto-axial myodural bridges are dynamic structures “moving” the dura. En block resection of the myodural bridges (4 HERDA and 5 controls) was accomplished and histopathology showed myofiber degeneration in 3 HERDA horses and 1 control. Ultrastructural examination revealed loosely packed collagen fibrils with abnormal orientation in all HERDA horses compared to mild abnormalities in 2 controls. Our study provides necropsy and ultrasonographic evidence of the dynamic aspect of the myodural bridges as dural sac stabilizers. Myodural bridges may be pathologically altered in connective tissue disease as evidenced by the ultrastructural morphology in the HERDA myodural bridge.

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.

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.