Research Funded by Ehlers-Danlos National Foundation
Margaret Casal, DVM, PhD
Section of Medical Genetics
The primary goal of this project was to provide a large animal (canine) model of the Ehlers-Danlos Syndrome (EDS) to mechanism of disease. A female Labrador retriever with an autosomal dominant form of EDS was donated to the Section of Medical Genetics at the Veterinary Hospital of the University of Pennsylvania for characterization and expansion of this canine model. Initial studies included the identification of the defective gene and characterization of the disease to further strengthen the EDS dog as a model for the human disorder. To this end, skin biopsy samples were obtained from each dog under local anesthesia (as is routinely done in the clinical setting for canine patients), radiographs (X-rays) of all limbs were taken, and breeding studies are still being performed to confirm the mode of inheritance. Skin biopsy samples were examined by routine microscopy and electron microscopy. The biopsy samples were also examined for elasticity (tensile strength) and fragility. The hearts of all dogs were examined routinely by auscultation (stethoscope), EKG, and echocardiography (ultrasound of the moving heart).
In summary, our dogs show not only the same clinical and pathological features as humans with EDS but they also have the same problems with medical management such as placing IV catheters and local lidocaine application. Future experiments are directed at developing better methods for placing IV catheters, more effective local anesthetics and understanding reasons why the skin does not react to local anesthetics as it does in normal dogs. The ultimate goal is to use the EDS dog for treatment trials that would be curative rather than just palliative. We are in the process of establishing collaborations with the research dermatologists at The Thomas Jefferson University in Philadelphia, that have been using iRNAs (interfering RNAs) in mice with EDS. The iRNAs are designed to interfere with the production of the abnormal collagen molecule, so that only the normal fibers are generated. The funding received through the NORD Foundation has enabled us to generate results that have led to submission of an NIH grant to further study clinical care and treatment of this and the other genetic skin diseases we work with.
While we have not found the defective gene yet, we have been able to further establish the dog as a model for the Ehlers-Danlos Syndrome in humans through the generous funds provided to us by the National Organization for Rare Disorders. The affected dog has now been bred twice to unrelated sires of different breeds and produced normal and affected puppies, demonstrating an autosomal dominant mode of inheritance, as is commonly the case in humans with EDS. We have retained all of the affected dogs, which have skin and joint laxity that far exceeds that of any normal dog we have in our colony. All dogs have luxated hip joints, but do not appear to have pain associated with it. They are able to run and play like most other dogs. Other clinical features include frequent skin tears which heal fairly well, but lidocaine used to prevent pain while suturing the wounds does not appear to be as effective as in normal dogs. Therefore, we place the dogs under general anesthesia when suturing the wounds or when skin biopsies are obtained. Also, placing IV catheters is not as easy as it is in normal dogs: the veins frequently blow, and we have found that placing butterfly catheters and using vet wrap (a material that only sticks to itself and not to the skin or hair) to hold the butterfly in place serves our needs. We have not found any abnormalities when examining the hearts of both dogs, but we will continue to follow the heart and the greater vessels by ultrasound to rule out abnormalities that may develop. Experiments performed on skin biopsy samples (1 cm x 2.5 cm) show that the skin stretches 4 times as farther than that of a normal size-matched dog. Once the skin reaches its maximum stretch, it tears at a minimum weight of about 900 g versus > 10 kg in a normal dog. Histology and electron microscopy show abnormal collagen arrangement as is to be expected.
Currently, we have included in our clinical evaluation protocol routine eye examinations that include pressure measurements and retinal assessment. The heart examinations are performed by Dr. Meg Sleeper, a board certified cardiologist and the eye examinations are performed by Dr. Andras Komaromy, a board certified ophthalmologist. Exciting new techniques have become available for the study of the defective proteins in these dogs. With the tissue culture we were able to establish from a 2 mm diameter biopsy sample, we can now compare skin proteins from normal and affected dogs to easily determine the abnormalities. This will allow us to find the defective gene which is necessary not only to understand the disease better but also to develop new therapies.