Sauer Quarter Horses



Genetic disorders -

Below is the basic description of the currently known five genetic disorders found in stock horses such as Quarter Horses, Paints, Appaloosas, Morgans etc. ALL breeding horses should be tested prior to being bred.


Hereditary Equine Regional Dermal Asthenia (HERDA) also known as  Hyperelastosis Cutis (HC) is a genetic skin disease predominately found in the American Quarter Horse. Researchers at Mississippi State University and Cornell  University believe that the origin of this genetic disorder may be the Poco Bueno's sire line. Symptoms of this disorder is a lack of adhesion within the layers of skin due to a genetic defect in the collagen that holds the skin in place. This defect causes the outer layer of skin to split or separate from the deeper layers sometimes tearing off completely. Areas under saddle seem to be most prone to these lesions often leaving permanent scares, preventing the horse from being able to be ridden. The disorder is recessive, which means that a horse must be homozygous positive or have two copies of the defective gene to suffer from the disease. Consequently both the sire and the dam must possess at least one copy of the mutated gene in order for the offspring to be afflicted.  Offspring born with one copy of the defective gene and one non-defective copy are considered a carrier and have a 50% chance of passing the defective gene on. 

Glycogen Branching Enzyme Deficiency (GBED) is a fatal condition caused by the bodies inability to properly store sugar.  In a normal horse, the body stores sugar as energy by converting glucose to glycogen. This inherited disorder prevents the body from producing the enzyme needed to branch the glycogen structure, preventing the horse from being able to adequately store the sugars. This means that the horse will not be able to store enough energy to fuel important organs, such as the muscles and brain. Foals born affected by GBED suffer from a range of symptoms associated with this lack of fuel, such as low energy, weakness, and difficulty rising. Other symptoms include low body temperature, contracted muscles, seizures, and sudden death. Unfortunately, GBED  is always fatal. Most affected foals will die before the age of 8 weeks. GBED often causes fetuses to be aborted in-utero. Research suggests that as many as  3% of aborted Quarter Horse foals were homozygous for the GBED mutation. Studies show that the mutation responsible for GBED is carried by as  many as 10% of Quarter Horse, Paint Horse breeds and related breeds. GBED is an  autosomal recessive trait, meaning a foal can only by affected if the foal inherits the disease from both parents. Horses that are carriers of the GBED have one copy of the mutation, but do not have any symptoms associated with the disorder. This makes DNA testing important to screen for carriers and prevent this fatal condition from occurring.  The mutation, which causes this disease, has been identified by Dr. Stephanie Valberg and Dr. James Mickelson of the University of Minnesota.

Hyperkalemic Periodic Paralysis Disease (HYPP) is a muscular disease that affects both horses and humans. In horses, HYPP has been traced back to one AQHA registered horse named Impressive and has the alternative name, Impressive Syndrome, named after this horse. Symptoms of HYPP may include muscle twitching, unpredictable paralysis attacks which can lead to sudden death, and respiratory noises. Severity of attacks varies from unnoticeable to collapse or sudden death. The cause of death is usually respiratory failure and/or cardiac arrest. The HYPP gene is dominant so both homozygous positive (HH) and heterozygous (nH) will cause this muscular disorder. Only homozygous negative (nn) has no HYPP effect. Since HYPP is dominant, the effects of it can also be transposed to other species of horses when intermixing occurs. This makes the recognition and elimination of this disorder very important in preserving the inherited health of all horses. 


Polysaccharide storage myopathy (PSSM) or Equine Polysaccaride Storage Myopathy (EPSM) is a glycogen storage disorder that results in the excess storage of sugar in skeletal musclesin the excess storage of sugar in skeletal muscles. It is often the cause of the common form of tying-up in horses. Affected individuals can have such minor symptoms to go unnoticed or multiple episodes of tying up, to severe colic and recumbency. Two types of PSSM have been identified. Yet, a simple DNA test currently only exists for Type 1. Horses with a single dominant gene WILL EXPRESS the disorder (at some point) AND can pass it to their offspring 50% of the time. Horses with two dominant genes will always produce afflicted offspring. Horses on forage based, low carb diets (little to no grain) may NOT exhibit symptoms since the condition is related to sugar storage. For that reason AND the bloodline source(s) is still unknown, this is a "best to test" genetic disease.  

Malignant Hyperthermia is an inherited dominant disease identified in Quarter Horses, Appaloosas and Paints that can cause severe typing up and even death when horses are subjected to anesthesia. A gene mutation causes a dysfunction in skeletal muscles resulting in excessive release of calcium inside the muscle cells which results in a hypermetabolic state and/or death. Symptoms include fever, excessive sweating, elevated heart rate, irregular heart rhythm, shallow breathing, muscle rigidity, and death. Horses who also have Polysaccharide Storage Myopathy (PSSM) can exhibit more severe symptoms of tying up, even without anesthesia. Horses with a single dominant gene express the disorder (at some point) and can pass it to their offspring 50% of the time. Horses with two dominant genes will always produce afflicted offspring. The only prevention is to not breed MH positive individuals.

We test our horses through UC Davis and highly recommend them for all your genetic testing. They work with AQHA as well. Click the banner below to open their website in a new tab-