Last fall, Ashley Williams thought she might be losing it. In January of 2004, Williams, a Thoroughbred and sport horse breeder and trainer from Ocala, Fla., bought a promising Thoroughbred filly from the Ocala Breeders’ Sale. That November, the yearling was put down and her body donated to support research efforts into a disease that a few months before, nobody believed the filly could possibly have–Degenerative Suspensory Ligament Desmitis.

DSDL is a connective tissue disease that’s most commonly recognized when it affects the weight-bearing structures of the suspensory ligaments, but researchers now know it can be found in fibrous connective tissue throughout the horse’s body.

In DSDL, the normal repair processes of the collagen fibers that compose these tissues break down. When this occurs in the suspensory, pain, lameness and thickening of the ligaments results, and in some cases, the fetlocks sink toward the ground. Such manifestations are just the tip of the iceberg, with researchers continuing to identify the extent to which it can affect other parts of the body.

First recognized in the Peruvian Paso in the late 1970s and most commonly associated with that breed, DSDL has now been diagnosed in breeds as varied as warmbloods, Quarter Horses and Standardbreds.

Thanks to the persistence of Williams, its presence in Thoroughbreds has also been confirmed. This diagnosis should serve as a wake-up call to breeders because there’s no cure or effective treatment for DSLD and researchers say it’s a genetic disease.

“Peruvian Pasos amount to zero dollars, not even a blip on the map of the equine industry. All the research up to now has been private money within our own breed,” explained Jeanette Mero DVM, of Romulus, N.Y., who founded DSDL Research Inc., in October 2000 to help raise awareness and research funding for the disease after she became involved with Peruvian Pasos.

Mero assisted with the clinical aspects of recent research efforts and has developed a diagnostic protocol for identifying the disease. Although she’s witnessed the devastating affects of DSDL on horses and their owners, Mero doesn’t believe its discovery in other breeds is a cause to panic.

“I certainly don’t think it’s an imminent threat to the Thoroughbred breed, but I’d like to not see them do what the Peruvian breed has done and bury their heads in the sand,” she said. “If they want to protect the athletic function of their breed, this is certainly something that would affect it. Why not stomp on it now before it gets any bigger?”

Mero said that many veterinarians, as well as horse owners, aren’t familiar with DSDL. “Because it’s almost always a bilateral disease or even in all four limbs, and a lot of animals have such tremendous heart, an owner won’t see an obvious head nod or lameness,” she said. “And these horses are still willing to go out there and do their jobs despite being affected, and it’s a shame.”

Currently, with no treatment options available, keeping affected horses comfortable is the objective.

“I tell people to think of it as you would an animal with arthritis. Lots of low-level moving around, keeping them lubricated is better,” said Mero. “Owners with affected animals will always note that if they do have to stall them overnight, the next morning the animal can hardly move.”

Hope For Future Horses

The filly Williams purchased that fateful day was named South Beach Baby (Line In The Sand–Miss Starquest), but she was soon dubbed “Hope.”

“She was a fantastic mover. I bought her and brought her home and didn’t notice anything until five months later when she stated dropping a little in her back pasterns,” Williams recalled. “And that’s when it all started.”

Initially, Hope wasn’t at all lame, but she did experience frustratingly regular and inexplicable bouts of colic, which were later attributed to DSLD. As soon as Williams saw her dropping in her pasterns, she called out the first of many vets.

“I was treated like I was being anal because I knew my horse and was defending my horse. I was told to chalk it up as a conformational defect and move on,” she said. “I started researching online and everything kept pointing to DSLD. I started asking these vets about it, and they said it was absolutely not possible; it only happened in Paso Finos. I was basic-ally told I was crazy.”

The striking visual similarity between Hope’s condition and the photographs of horses with DSLD Williams found online spurred her to call Mero, whose website (www.dsld.org) she’d been reading.

“Even she said, ‘You know, it’s really kind of impossible, but I really want to see her,’ ” said Williams, who quickly sent her photos of the filly.

Mero called within hours of seeing the photos to say that she suspected Williams was right and if she was, it was a very big deal because hers would be the first confirmed Thoroughbred case.

“I was almost grateful because, at that point, I’d fought with so many people about it, and now I could fix it. I didn’t know there was no cure,” she said.

After receiving Mero’s diagnostic protocol, Williams called friend Mindy Sharp, a veterinarian from the local Peterson & Smith Veterinary Hospital, to administer the exam. As is common with the disease, Hope alternated between phases of relative soundness, where she would be able to get around with a stiff-legged “robot-like” gait, and periods when she was virtually immobilized and unable to stand. When Sharp arrived, she was in a sound phase.

The physical exam outlined in the protocol involves evaluating conformational changes, such as swollen, dropped fetlocks with straightened leg angles (this only occurs in approximately half of cases, even those far advanced); palpating the suspensory ligaments for pain and enlargement; checking for baseline lameness, although as a disease affecting pairs of limbs, horses usually just appear stiff; and performing flexion tests, which are always positive, despite the degree of severity.

Following the physical exam, an ultrasound is performed. As stated in Mero’s protocol, “What distinguishes DSLD apart from just an injury is the progressive, continual enlargement of the suspensory ligaments, primarily in the branches, over time, in more than one limb. Early onset cases often are only slightly enlarged and may warrant a second exam in three to six months to document continual enlargement.”

Hope had already obviously failed the first three aspects of the physical exam with her dropped, swollen and sore fetlocks and extreme stiffness, and the flexion test and ultrasound confirmed their suspicions.

“We tried flexing her in the back and the poor filly just hit the ground, which, of course, brought me to huge tears,” said Williams, who soon realized the filly had to be put down.

The results of all the tests in hand, Mero was interested in having the filly shipped to Cornell University in New York for study, but Williams didn’t want to subject her to the trip. She agreed to send her to the University of Florida, where she would be euthanized and her organs harvested for research. The decision was an agonizing one for Williams, but she made the choice in hopes of benefiting other horses by helping researchers unravel some of the many mysteries still surrounding the disease.

“Veterinarians from six universities came down. The last few days she was alive, she was treated like a princess,” she said. “If she came to me for this reason, to save other horses and people from this, I was going to do it. It was the hardest thing for a horse owner to do.”

Hope was euthanized on Nov. 16, 2004, only four days after Sharp’s exam and nine months after she was purchased as a healthy, beautifully moving sport horse prospect. Necropsy revealed the disease had attacked her front and back legs, the main arteries in her heart, her stomach lining and her liver.

Although the experience took a huge emotional and financial toll on Williams, she’s comforted in knowing that her perseverance may help shed some light on this disease.

“If she was at some huge breeding farm where she was out in a big pasture and no one ever saw her, she would have just died and they would have just chalked it up as, ‘Oh, she colicked’ or something. They would never have gone to the extreme that I went to,” she said. “It was not something that was cheap, but [diagnosis] isn’t expensive if you start out with the protocol and have them tested.”

Looking For Answers

There are still many unknowns surrounding DSDL, and the “how” and “why” it occurs rank at the top of the list. Mero, who has worked closely with pathologist Roy Pool DVM, a pioneer in the disease’s research efforts, explained his school of thought on the basic mechanism by which the disease develops.

“Any minute of every day, your body tissues are undergoing wear and tear and a normal amount of repair that goes on. [In the case of DSDL] the collagen is not being repaired so you see a ton of immature collagen overloading the tissue. Instead of seeing mature collagen, you see little, tiny fibrils of immature collagen, which are very weak,” she explained. “You find connective tissue and collagen throughout the body. We see the disease predominantly in the suspensory tissue probably because that’s a weight-bearing substrate, but when we look at these animals in necropsy, you do find it all over.”

In extreme cases, the normally uniform tissue may even contain pieces of cartilage or bone that have formed as a by-product of the malfunctioning repair system.

What starts this system malfunction is not yet known. “But the end result is this blob of tissue. Connective tissue should be pliable and flexible and should have some give and take, and all of that is gone,” said Mero.

To find some of these answers, two major research efforts analyzing different components of the disease are occurring at the University of Georgia and University of Kentucky.

The Kentucky team is trying to find a marker that would identify carriers to provide a way to selectively breed against the disease. “We’re in the process of doing a genomic scan. We’re testing the genetic markers that are spaced over all the chromosomes of horses, looking for differences between affected and non-affected animals in the expression of the markers,” explained Gus Cothran, Ph.D., director of the University of Kentucky’s Equine Parentage Testing and Research Laboratory.

Cothran and his team have tested more than 200 markers thus far and have found seven places where there are statistical differences between affected and non-affected horses. From that information, they’re trying to identify the gene or genes responsible for the disease and determine how it is passed down family lines.

The horses in their current study are all Peruvian Pasos, but he hopes that if the same gene isn’t the culprit in other breeds, their work with Peruvians will give them an excellent head start in other horses. “We know that even conditions in horses with identical pathology are not necessarily caused by the same gene,” said Cothran.

“At Georgia, they’re focusing on the pathology of the disease. Their next move is to look at the biochemistry involved. If they’re able to pinpoint a difference in the biochemical structure of the suspensory ligament between affected and unaffected horses, that could tell us biochemically what gene to target,” explained Cothran. “Some of their preliminary work supports where we’re looking right now.”

Cothran said that the biochemical and genetic differences found in affected animals needs to be identified before the cause of the disease could be understood.

“Generally what happens is some enzyme or protein in the pathway that leads to the development, repair or whatever’s going on, doesn’t function right. Because some mutation causes the protein not to be built pro-perly, it doesn’t function right,” he explained.

The initial hope for this research is the development of genetic and blood tests that will identify DSLD carriers, which will help breeders stop the disease’s propagation.

“But, obviously, the whole reason so much work is being done is, generally, if you can identify the cause, you can maybe find ways to develop a cure,” said Cothran. “Until we know what it is, there’s no way to know if there’s something we can do or not.”