Funding provided by Ehlers-Danlos National Foundation
Margret Casal, Dr med vet, PhD, Dipl. ECAR
Section of Medical Genetics
School of Veterinary Medicine
University of Pennsylvania
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).
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. Our breeding studies are highly suggestive of an autosomal dominant mode of inheritance, as one normal and two pups affected with EDS were born to an affected mother that was outcrossed to a completely unrelated sire. One puppy was so severely affected that he was stillborn. The other affected puppy is now 7 months old and shows the exact same clinical signs as her mother. The mother is pregnant again and we expect puppies in a few weeks. Both dogs have skin and joint laxity that far exceeds that of any normal dog we have in our colony. Both 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 are in the process of collaborating with Dr. Ron Minor from Cornell in NY, who is the world’s leading expert in collagen defects in animals to find the mutation. We are also using special stains and new techniques to examine the microscopic features of the disease in our dog model. We will continue to document disease features as they appear. 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.
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.
To date, over 350 genetic diseases have been described in the dog, many of which are analogous to human genetic diseases. The number of canine models used for the study of inherited diseases is rapidly growing and dogs have been invaluable for the understanding of both disease processes and a variety of therapies. The EDS dogs offer an excellent model to use to understand disease mechanisms and ultimately to develop and test different treatment modalities. The clinical presentation of the EDS dog is more similar to the disease in humans than the current mouse model. The dog is also a long-lived, large animal that more closely resembles the size of a child, making it a valuable model for preclinical trials and long-term studies. Because of the dog's size and long life span, more samples can be obtained and pathology can be followed for a very long period of time.