Gene-based medicine for equine muscle disorders

Gene-based medicine for equine muscle disorders

Horse genome research is improving understanding, diagnosis, treatment of patients
Mar 01, 2009

Photo 1: This foal has congenital flexure deformities of both front limbs. The right front is more severely affected, and the contracture of the deep digital flexure tendon has positioned the foot on the toe in the characteristic "ballerina" posture. The left fore is not as severly affected but a credit card still slides easily under the heel of the foot.
Researchers knew that the equine genome project eventually would lead to monumental discoveries and new methods of diagnosis and treatment of significant benefit to the horse.

Once the gene sequence, or DNA map, of the horse was completed, they could investigate abnormalities or "breaks" in that code. These abnormal genes could be identified and tests developed to look for their presence — all leading to better diagnosis.

Photo 2: PVC toe extensions were placed on the foal to attempt to stretch the tendons and return the limb to a more normal position.
Conditions that appeared clinically similar but which had different causes and etiologies could now potentially be distinguished from one another. Scientists hoped that further research would then lead to genetic modification therapy aimed at repairing those DNA abnormalities and allowing clinicians to treat and possibly cure some gene-based diseases.

Photo 3: The same foal 30 days later, after toe extension treatment.
While the veterinary community has not accomplished the repair-and-treatment phase just yet, the identification and diagnosis aspect of gene-based medicine is well under way.

One area that has benefited greatly from this is muscle disease in the horse. Muscle dysfunction — ranging from a mild, chronic stiffness or poor tone and development all the way to the massive contracture and severe spasms seen in full-blown rhabdomyolysis or tying-up cases observed in varying breeds and sports disciplines — is a common problem in performance horses.

Clinicians have long been frustrated with these cases because many of them appear outwardly similar — tight to spastic muscle. The Quarter Horse roping mare that displays a consistently stiff hind-limb gait with slightly elevated muscle enzymes (creatine phosphokinase (CPK) and aspartate transaminase (AST, also called serum glutamic oxaloacetic transaminase, or SGOT) looks very much like a Dutch Warm Blood gelding experiencing the same short-strided gait and muscle stiffness. The tied-up endurance horse that, at 35 miles of a 100-mile event, stands sweating profusely, unable to move and producing classic coffee-colored urine, presents as similar a clinical picture as the young Thoroughbred in race training that also ties up after a relatively short but intense training gallop.

Photo 4A: Sonny, an endurance horse, tied up after running 40 miles at an event. The horse is sweating, has mild colic and shows the characteristic swollen, hard muscles typical of this condition. The owners placed a blanket on the hard rump muscles to keep them warm prior to treatment with intravenous fluid.
Veterinarians looking at all of these horses with their similar variations of tying-up-like signs and investigating their histories, uses, diets and other management factors, generally have been unable to connect them.