Connective Tissue Disorders in Domestic Animals

Though soft tissue disorders have been recognized and described to some detail in several types of domestic animals and small mammals for some years, not much progress has been made in our understanding of the biochemical basis and pathogenesis of these diseases in animals. Ehlers-Danlos syndrome described in dogs already in 1943 and later in cats affects mainly skin in these animals. The involved skin is thin and hyperextensible with easily inflicted injuries resulting in hemorrhagic wounds and atrophic scars. Joint laxity and dislocation common in people are less frequently found in dogs. No systemic complications, such as organ rupture or cardiovascular problems which have devastating consequences in people have been described in cats and dogs. The diagnosis is based on clinical presentation and on light or electron microscopic features of disorganized and fragmented collagen fibrils. Several cases of bovine and ovine dermatosparaxis analogous to human Ehlers-Danlos syndrome type VIIC were found to be caused by mutations in the procollagen I N-proteinase (pnPI) or ADAMTS2 gene, though mutations in other sites are likely responsible for other types of dermatosparaxis. Cattle suffering from a form of Marfan syndrome were described to have aortic dilatation and aneurysm together with ocular abnormalities and skeletal involvement. As in people mutations at different sites of bovine FBN1 may be responsible for Marfan phenotype. Hereditary equine regional dermal asthenia (HERDA), or hyperelastosis cutis, has been recognized in several horse breeds as affecting primarily skin, and, occasionally, tendons. A mutation in cyclophilin B, a chaperon involved in proper folding of collagens, has been identified in some cases. Degenerative suspensory ligament desmitis (DSLD) affects primarily tendons and ligaments of certain horse breeds. New data from our laboratory showed excessive accumulation of proteoglycans in organs with high content of connective tissues. We have identified an abnormal form of decorin with altered biological activity in these proteoglycan deposits, and more recently changes in processing of aggrecan were found by us and other investigators. The naturally occurring diseases of soft tissues in domestic animals described here have a potential to serve as good models for analogous human diseases. This is the case particularly relevant to dogs as a half out of the more than 400 naturally occurring hereditary canine diseases has the potential to serve as a model for human disease.