Dermatosparaxis in two Limousin calves

Dermatosparaxis is an inherited connective tissue disorder in animals primarily recognised by extreme fragility of the skin [1, 2]. The human condition Ehlers-Danlos syndrome (EDS) type VIIC (EDS type VII) is due to a similar biochemical defect in post translational modification of collagen [3]. Although the two skin conditions have analogous pathogeneses, there are marked phenotypic differences. In humans clinical signs include joint laxity with less skin hyperextensibility and fragility than is seen in affected animals [4]. There are marked species and intra-species differences in the expression of the phenotype and the disease has been more aptly described as an Ehlers Danlos Like condition in animals [5]. The condition results from the absence of activity of an enzyme (procollagen I N-proteinase (pNPI)) which normally excises the N-propeptide of type I and type II procollagens resulting in formation of mature collagen. When this enzyme is deficient, there is accumulation of pre-cursor molecules (pro-collagen) that self-assemble into ribbon-like fibrils that fail to provide normal tensile strength to tissues [6]. In normal connective tissue this enzyme excises the amino terminal peptide extension on the precursor molecule to produce collagen. The resulting dysfunctional procollagen in the dermis is poorly structured and loosely arranged, giving rise to hyperextensibility and poor elasticity in the skin of affected animals [1].

Dermatosparaxis has been reported in humans [7], cattle [2], sheep [8], cats [9], horses [10], dogs [11], mink [12], rabbit [5] and buffalo [13]. Cattle breeds affected include the Belgian Blue, Charolais, Hereford, Holstein, Simmental and crossbred cattle [14, 15]. There are no reports of the condition in the Limousin breed.

An autosomal recessive mode of inheritance has been described in Belgian Blue cattle associated with a deletion or single nucleotide substitution that results in a premature stop codon in the “ADAM metalloproteinase with thrombospondin type 1 motif 2” (ADAMTS2) gene. This leads to abnormal processing of procollagen 1 [16]. The recessive nature of the gene was highlighted by the fact that the disease first occurred after inbreedings [2]. However, in a herd of Drakensberger cattle in South Africa where dermatosparaxis occurred, this known mutation was not found [17]. Furthermore, other cases of the condition in other cattle breeds have not been subject to detailed genetic investigation [18].

In December 2015 two Pedigree Limousin calves (1 male and 1 female) were presented to the University Veterinary Hospital (UVH) at University College Dublin (UCD). Both were full siblings born to recipient heifers from implantation via embryo transfer. The two calves presented two days apart. The first (Calf A) was a 12-h-old bull calf born unassisted but from birth remained in lateral recumbency and was unable to maintain a normal posture even when assisted. The calf was non-responsive and appeared grossly abnormal, as the skin over the thorax and abdomen was moist (Fig. 1a). The orbital fissures were almond shaped with bilateral clouding of the cornea (Fig. 1b). The calf had thick folds of cervical skin and, on closer inspection, had multiple small fissures in the skin over large parts of the body, particularly over joints and the medial aspect of the hindlimbs (Fig. 1c). Whilst examining the skin more cracks appeared even following gentle manipulation. Additionally this calf displayed involuntary muscle tremors that had been occurring since birth. The calf was euthanised and submitted for post mortem examination. Two days later a second Pedigree Limousin calf (Calf B) presented to the UVH, a female with similar clinical features as Calf A. In addition, Calf B had a ventromedial strabismus bilaterally and pale mucous membranes. This animal was also euthanised and submitted for post mortem examination. Both calves were euthanised using intravenous pentobarbital sodium (Release, 5 ml/10KG BW).

Post-mortem examination revealed the skin of Calf A to be diffusely moderately thickened, with linear fissures noted over the lateral neck, dorsum, and on the flexor surface of the limb joints, axillae, and groin. Occasionally the underlying dermis was exposed. The skin was diffusely damp; the oral mucous membranes were red. Bilaterally, the second incisors were small and subgingival. Calf B had similarly thickened, damp skin, with loose fragments of crusty skin in the regions where the fissures were seen in Calf A. Internal organs of both calves appeared normal; however, there were focally-extensive haemorrhages in the abomasal mucosa of Calf A, with similar, smaller, lesions in Calf B. In both animals the abomasum contained large amounts of clotted milk, but the remainder of the gastrointestinal tract were empty. In addition, there was a small focus of tortuous, dilated blood vessels on the diaphragmatic surface of the spleen of Calf A. All limb joints of Calf B contained a small amount of serosanguinous fluid.

Multiple tissues were sampled from the carcasses for histopathologic processing. Briefly, tissues were fixed in 10 % formalin, dehydrated in alcohol, embedded with wax, cut into 5 μm sections, and mounted on glass slides. All tissues were stained with haematoxylin and eosin (H&E). A selection of skin samples were also stained with periodic acid schiff (PAS), Masson’s Trichrome, and Alcian blue using routine protocols. The Alcian blue stain was employed to look for acid polysaccharides which are found in the ground substance of skin, there was no increase in ground substance in these cases. Tissues were examined using light microscopy by pathologists at UVH UCD and the Joint Pathology Centre, Maryland, U.S.A.

Histologically, the skin of Calves A and B exhibited a marked diffuse reduction in the density and number of mature collagen fibres, preferentially affecting the superficial dermis. The remaining fibres were short, fine, pale, fibrillated and fragmented. Trichrome staining by the Masson’s method further highlighted these abnormalities, confirming the dysplastic nature of the collagen. Collagen fibres of the deep dermis appeared relatively spared. Calf B exhibited similar, but less severe, changes (Figs. 2d; e). Ultrastructurally, abnormal dermal collagen fibres of the haired skin of the back consisted of irregular fibrils arranged in loosely woven, twisted flat, and/or helical ribbons with irregularly spaced or lost transverse striations (Fig. 3).

Ten nanogram of DNA was used for each PCR, reactions were performed in 25 μl and contained 17.5 μl water, 1 AmpliTaq Gold buffer, 2 μl primer mix, 1.5 mM MgCl2, 0.5 μl dNTP mix and 1U of AmpliTaq Gold. The thermal cycling conditions consisted of an initial activation step of 95 °C for 5 min followed by 35 cycles of 94 °C for 30 s, 56 °C for 45 s and 72 °C for 1 min with a final elongation step of 72 °C for 5 min. PCR products were analysed using the Agilent DNA 1000 chip. The PCR product from all DNA samples, both cases and controls, yielded a single sharp band at the expected size of 101 bp, and no deletions, indicating that the genetic defect in these animals is not the same as described previously [6].

The clinical and pathological features described in these two calves are consistent with a diagnosis of dermatosparaxis [1, 2, 16, 17] and is the first reported case of this disease in this breed. The skin fragility and hyperhidrosis, along with the marked fragmentation and depletion of superficial dermal collagen, are consistent with previous bovine cases [1]. Interestingly, the PCR testing carried out in this case did not find a mutation in the ADAMTS gene described previously in cattle. [6, 15] and was similar to the absence of this mutation in Drackensberger cattle [17] highlighting the fact that a range of mutations can result in a broadly similar disease phenotype [5]. Inbreeding has previously been incriminated as the underlying mode of inheritance in Belgian Blue cattle [2] and in the Charolais breed [18]. In the current case, there is common parentage in the ancestry; the dam’s great grandsire and the sire’s grandsire were the same bull.

This case report highlights the first case of this inherited skin disease in the Limousin breed. The recessive nature of inheritance previously described may suggest that the genetic anomaly is present in the population in a heterozygous state and thus can be preserved [2]. This case also highlights the potential risk of the widespread and rapid dissemination of genetic diseases associated with embryo transfer. In this case, as the specific genetic defect was not identified and considering the lethal nature of the phenotype observed in these calves, we feel further genetic investigation is warranted in order to identify the causative mutation. This information can then be used to screen for the condition in pedigree Limousin animals used to maintain the genepool. Limousin is a popular breed internationally, and raising awareness of this disease should allow the necessary measures to be put in place to minimise its dissemination.