Some horse organizations have instituted rules to attempt to eliminate this widespread disease. The American Quarter Horse Association (AQHA) mandates testing for foals descended from Impressive if both of the foal's parents were not homozygous negative (N/N) for the gene,[1] and, since 2007, has not registered foals homozygous (H/H) for the gene.[2] Since 2007, the Appaloosa Horse Club (ApHC) has required foals descended from Impressive to be tested, so that the results may be recorded on its certificate.[3] The American Paint Horse Association (APHA) mandated that, after 2017, stallions must be tested for HYPP so that mare owners may make an informed decision before choosing a stallion for breeding to their mare.[4]