Hereditary equine regional dermal asthenia facts for kids

Hereditary equine regional dermal asthenia (HERDA), also known as hyperelastosis cutis (HC), is a genetic problem found in horses. It's like a weakness in the "glue" that holds the skin to the rest of the body. This happens because of a faulty gene. Horses with HERDA have very delicate skin that tears easily. Their skin also has trouble healing. In these horses, the skin layers separate. There is no cure for HERDA. Most affected horses get an injury they cannot heal. Because of this, they are often put to sleep to prevent suffering. The only way to stop the disease from spreading is to be careful about which horses are bred.

Which Horses Get HERDA?

This disease is mostly found in American Quarter Horses. It is especially common in lines of horses used for cutting, which is a type of horse sport. Researchers have found that affected horses can be traced back to a famous stallion named Poco Bueno. It's possible the problem goes back even further to his ancestors.

Scientists have named four Quarter Horse stallions who were carriers of the gene and had at least one HERDA foal. These stallions are Dry Doc, Doc O'Lena, Great Pine, and Zippo Pine Bar. All these horses are related to Poco Bueno through his son, Poco Pine, and his daughter, Poco Lena. Other horse breeds can also get HERDA. These include the American Paint Horse and the Appaloosa. Any breed that allows breeding with American Quarter Horse Association (AQHA) horses might also see HERDA.

Signs of HERDA

HERDA causes unusual skin along a horse's back. This skin tears or rips very easily. When it heals, it often leaves noticeable scars. The skin on affected horses is also loose and very stretchy. This problem with their skin's "glue" (collagen) can also affect their heart valves. These valves are not as strong as they should be.

Signs of HERDA usually appear when a horse is around two years old. This often happens after the horse experiences pressure or an injury on its back, neck, or hips. However, some foals can show signs if they get hurt. Other horses might grow up and only show signs in their joints. How HERDA shows up can be different for each horse. Scientists are still learning about all the ways it can affect horses.

Testing for HERDA

You can find out if a horse has HERDA by doing a DNA test. This test uses a blood or hair sample. The results will show one of three things:

• N/N — Normal: This horse does not have the HERDA gene.
• N/HRD — Carrier: This horse carries one copy of the HERDA gene. It can pass the gene to its foals.
• HRD/HRD — Affected: This horse has two copies of the HERDA gene. It will have the disease.

Living with HERDA

Horses affected by HERDA usually live for only 2 to 4 years. There is no cure for this disease right now. To stop HERDA from happening, the only solution is to avoid breeding two horses who both carry the HERDA gene.

History of HERDA

Discovering the Disease

The disease was first recognized in 1971. Researchers studied horses with HERDA. They found that 95% of these horses could be traced back to Poco Bueno on both sides of their family tree. Some horses also traced back to his full brother, Old Grand Dad. The remaining 5% traced to King, who was the father of both Poco Bueno and Old Grand Dad. This suggests that Poco Bueno might have inherited the HERDA problem from his father, King. It's possible the condition goes back even further. It is hard to trace it more because old family trees do not clearly show all of King's relatives.

In 1988, a disease similar to HERDA was described in scientific papers. It talked about two related Quarter Horses that were affected. Researchers at Mississippi State University found that a one-year-old filly had skin that separated. This was linked to loose collagen fibers. In 2004, veterinarians at the University of California, Davis, first used the name "hereditary equine regional dermal asthenia" (HERDA). They had examined 50 horses with the typical signs of the disease. A key sign in all affected horses was that their deep skin had short and thin collagen fibers.

Tracing the Gene

Over the years, breeding horses that were closely related to Poco Bueno became more common. This is called inbreeding. It increased the number of horses that had two copies of the faulty gene. This led to more affected animals being born. In 2004, a report showed that 14 out of the top 100 cutting horse stallions were known HERDA carriers. Today, about 28% of all horses with cutting horse bloodlines carry the HERDA gene.

Developing the DNA Test

Scientists at UC Davis used DNA samples from horses with HERDA. They looked for parts of the DNA that were identical in affected horses. In January 2004, UC Davis announced they had successfully started mapping the gene. More work confirmed that the disease was inherited, not just caused by the environment. It strongly showed that a horse needed two copies of the faulty gene to get the disease.

In January 2007, UC Davis shared their findings. They announced they could identify horses that carry the HERDA gene. A full report of this work was published on May 11, 2007. It explained how they mapped the gene and found a specific change in the gene that makes a protein called peptidylprolyl isomerase B. At the same time, the Veterinary Genetics Laboratory at UC Davis started offering a genetic test. This test could identify carriers of the disease gene.

In the spring of 2007, researchers at Cornell University and the University of California, Davis, both announced they had developed a DNA test for HERDA. More than 1,500 horses were tested while the test was being developed. The test was then made available to the public through both universities. UC Davis was given a United States patent for the HERDA test on October 27, 2009.