They gave the muscular Quarter Horse colt an ambitious name: Impressive. He lived up to the name in such dramatic fashion that it became a household word in Quarter Horse circles – especially among breeders and exhibitors involved in showing halter horses.

Impressive sons and daughters were big, bold, and beautiful with defined musculature. They took the halter show ring by storm, racking up championships from one part of the country to another. Just as quickly, sons and daughters of the great stallion were in demand for breeding programs.

Then, the Impressive ship hit the sand.

A number of owners of Impressive offspring and second- and third-generation descendants of the stallion reported that some of these horses seemed to have acquired a muscle disease. Some would exhibit muscle tremors and with others there was even paralysis.

Enter Sharon Spier, DVM, PhD, an associate professor of the Department of Medicine and Epidemiology at the University of California, Davis. Spier led the effort by researchers to find out more about the disease and what caused it. The project began in 1989 and was funded by the American Quarter Horse Association.

The results of that research produced a bombshell for the Quarter Horse industry. Spier and her associates reported that the disease involved was Hyperkalemic Periodic Paralysis, known industry-wide today by the acronym HYPP.

Merely identifying the disease and the way it functioned, however, was not the bombshell. The bombshell came when it was reported that every single horse found with the disease traced to one stallion–Impressive.

The researcher’s report was published in the September 1992 issue of The Quarter Horse Journal, but Impressive was not identified by name. In the months that followed, there were rumors, speculation, and widespread concern within the industry.

The AQHA issued an official statement in the December 199