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For some time, evidence pointed to Poco Bueno as the culprit bloodline, but up until now, Winand says, inadequate case numbers limited information available to researchers.
It is not supposition at this point, Winand and Rashmir state. It is scientific fact. They say 95% of the horses they have identified with HC trace back to Poco Bueno through both their sires and dams, with a few tracing back to Poco Bueno’s full brother, Old Grand Dad. The other 5% trace back to Poco Bueno’s and Old Grand Dad’s sire King and perhaps even beyond. The statistical evidence, Rashmir says, is not just from Mississippi State and Cornell, but includes HC horses from around the country as veterinarians have shared information. “All of the horses diagnosed with HC are related,” Rashmir says.
Pinpointing The Start
Just where along the line did the mutation occur? Winand says: “As of this writing, pedigrees from approximately 100 well-documented cases have been examined. These show that 95% of the horses identified with HC trace back to Poco Bueno through both their sires and dams. The other 5% trace back to other horses in this sire line, including King, Zantanon, Little Joe, and Poco Bueno’s full brother Old Grand Dad. While this suggests that Poco Bueno may have inherited the HC mutation from his sire, this may not be the case. With the available information, it is difficult to rule out the possibility of Miss Taylor, Poco Bueno’s dam, transmitting the HC gene to Poco Bueno. It may never be possible to scientifically identify the origin for several reasons. We have no pedigrees to date that completely differentiate the lines of King versus Miss Taylor, and even if we did, it is difficult to verify the accuracy of pedigrees this far back, or further.”
Diagnosis of the disease is made via pedigree evaluation and clinical signs and can be confirmed with a skin biopsy. In a number of cases, the disease has surfaced when the horse is two years of age and goes into training. The weight, pressure, and movement of the saddle, compounded by the rider’s weight, often are enough to cause the skin to separate, There is some good news, the two researchers say. The genes that cause HC are recessive, and it takes two to tango. This means that both sire and dam must possess the recessive gene in order for an offspring to possibly be afflicted with HC.
In this way, the disease differs from hyperkalemic periodic paralysis (HYPP), which descended through the bloodline of the Quarter Horse stallion Impressive. HYPP is caused by a dominant gene that can be carried by only one of the parents and still cause the affliction. With HC, both parents must carry the recessive gene for the horse to be The HYPP gene has been identified, and horses can be tested for it through a DNA procedure. Researchers around the country are working to identify the HC gene, but estimates are that they might be a couple of years from success, barring some unforeseen scientific breakthrough.