There’s an interplay of genes, or genes and environmental factors, that are causing these problems. This is a disease in which the carriers are the problem, as horses affected by JEB do not survive long enough to breed.įrom a clinical perspective, polygenic, or complex genetic diseases, are more interesting and malleable. Carriers of the mutated gene present normally, and have no effects of the mutated allele.
Saddlebreds, Belgians and other draft type horses can be affected by JEB, a skin disease that becomes too painful for foals to humanely survive. These foals lack the enzyme needed to effectively store sugars, which results in the death of the foal. GBAD can be found in American Quarter Horses and Paint horses. Glycogen Branching Enzyme Deficiency (GBED)
They are unsafe to be ridden, and are often a danger to themselves as they frequently fall and are unable to stand again. This is a neurologic condition indicated by a lack of balance in foals. Homozygous foals present with a severely compromised immune system, and usually die from infection before their first year.Īnother condition found almost exclusively in Arabians, most Arabian breeders are on the lookout for CA and SCIDs when breeding now. The carriers, or heterozygote horses, are also affected, but present with a higher incidence of sarcoids. This autosomal recessive disease is found in Arabians. These foals do not survive long past birth. These foals have a lavender tint to their coat when born, and are very weak. This rare disease is found in the Arabian breed. This is also on the AQHA list of required genetic tests. These horses can’t be used as riding horses or breeding horses, and are generally humanely euthanized. This is indicated by hyper-extensible skin that begins sloughing off. HERDA presents in American Quarter horses, generally around two to three years of age, or when you start a horse under saddle. Hereditary Equine Regional Dermal Asthenia (HERDA) Of the autosomal recessive diseases, we have Hereditary Equine Regional Dermal Asthenia (HERDA), Lavendar Foal Disease, Cerebellar Abiotrophy (CA), Glycogen Branching Enzyme Deficiency (GBAD), Severe Combined Immunodeficiency (SCID), and Junctional Epidermolysis Bullosa (JEB).
The environmental stressors can have a large factor in how RER manifests. The horses also develop those melanomas at a younger age.Ĭommon in Thoroughbreds, Standardbreds, and Arabians, this is an autosomal dominant disease that is also modulated by the environment. It’s very rare to see a teenagaged grey horse that doesn’t have some melanoma. We’ve found that there’s an increased rate of greying in horses who are homozygous for this mutated allele, and an increased rate of melanomas to go along with it. Not restricted to certain breeds, Grey Horse Melanoma is a color associated disease. All three of these muscle conditions affecting Quarter Horses (PSM, HYPP and MH) are included on the five required tests for AQHA registration. Mostly affecting American Quarter Horses, this is another muscle issue that is also closely associated with PSM. This muscle condition also has symptoms similar to tying-up, with muscle stiffness, shifting lameness, and muscle tremors happening in bouts. PSM is more widespread, affecting American Quarter horses, Warmbloods (a group that is in general pretty genetically diverse), and draft breeds, among others. This disease is often mistaken for “tying-up” given the similar outward appearance. HYPP also affects heterozygous horses, and can be heavily modulated by environmental causes. AQH breeders look for the heavily muscled horses, breed to that line, and can end up with a horse with a severe genetic disease. This disease is directly associated with a single line of American Quarter Horses. Largely affecting the American Quarter Horse and American Paint Horse, HYPP is a disease which makes horses susceptible to unexpected paralysis or muscle tremors. Of the autosomal dominant diseases, you have Hyperkalemic Periodic Paralysis (HYPP), Polysaccharide Storage Myopathy (PSM), Malignant Hyperthermia (MH), Grey Horse Melanoma, and Recurrent Exertional Rhabdomylosis (RER). There are eleven mutations that are currently commercially tested for in the equine industry.
A lot of the diseases you know of actually have a genetic basis. Now we are diving into an overview of the different types of genetic diseases, and a few examples of each. We also conducted a seminar for our clients (video at the bottom) to discuss the basics as well as some of the genetic diseases that affect our horses. We started the genetics conversation with the basics of genetics, the history of genetic testing, and where we’re going next.