Lethal white syndrome is a rare but serious genetic disorder in horses, primarily affecting foals born with the overo coat pattern. This condition is characterized by a lack of nerve cells in the intestines, leading to severe digestive issues and, ultimately, death.
What is Lethal White Syndrome in Horses?
Lethal white syndrome, also known as overo lethal white syndrome (OLWS), is a genetic disorder linked to the overo coat pattern in horses. It is caused by a mutation in the endothelin receptor type B (EDNRB) gene. Foals affected by this syndrome are typically born with a completely white coat and blue eyes. The primary issue lies in their intestines, which lack the necessary nerve cells to function properly, leading to a condition called aganglionosis. This results in an inability to pass feces, causing severe colic and eventual death within a few days of birth.
How Does Lethal White Syndrome Occur?
Lethal white syndrome occurs when a foal inherits two copies of the mutated EDNRB gene, one from each parent. Horses that carry one copy of the gene are known as carriers and do not exhibit any symptoms. The condition is most commonly associated with the American Paint Horse, but it can also affect other breeds with the overo coat pattern, such as the Quarter Horse and Thoroughbred.
Genetic Transmission
- Homozygous Carriers: Foals with two copies of the mutated gene (homozygous) will develop lethal white syndrome.
- Heterozygous Carriers: Horses with one copy of the gene (heterozygous) are carriers and appear normal but can pass the gene to their offspring.
- Breeding Risks: Breeding two carriers increases the risk of producing a foal with lethal white syndrome.
How Common is Lethal White Syndrome in Horses?
The prevalence of lethal white syndrome is relatively low, primarily due to increased awareness and genetic testing among breeders. The syndrome is particularly associated with the American Paint Horse breed, where approximately 25% of horses carry the gene. However, the actual occurrence of affected foals is less common, thanks to responsible breeding practices.
Breeding Statistics
- Carrier Prevalence: About 25% of American Paint Horses are carriers.
- Affected Foals: The likelihood of producing an affected foal is 25% when two carriers are bred together.
How to Prevent Lethal White Syndrome
Preventing lethal white syndrome primarily involves genetic testing and responsible breeding practices. Breeders can test horses for the presence of the mutated EDNRB gene to determine if they are carriers. By avoiding the breeding of two carriers, the risk of producing an affected foal is significantly reduced.
Genetic Testing
- Purpose: Identify carriers of the lethal white gene.
- Process: A simple DNA test using hair or blood samples.
- Outcome: Helps breeders make informed breeding decisions.
People Also Ask
What are the Symptoms of Lethal White Syndrome in Foals?
Foals with lethal white syndrome are born with a completely white coat and blue eyes. Within hours to days, they exhibit signs of severe colic, such as restlessness, rolling, and inability to pass feces due to intestinal blockage. Unfortunately, the condition is fatal, and euthanasia is often recommended to prevent suffering.
Can Lethal White Syndrome be Treated?
There is currently no cure or effective treatment for lethal white syndrome. The lack of nerve cells in the intestines is a congenital defect that cannot be corrected. Veterinary intervention can provide temporary relief from colic symptoms, but the condition is ultimately fatal.
How Can I Tell if My Horse is a Carrier?
To determine if your horse is a carrier of the lethal white gene, genetic testing is necessary. The test is simple and involves analyzing a sample of the horse’s hair or blood. Results will indicate whether the horse is a carrier, non-carrier, or homozygous for the gene.
Are There Other Conditions Similar to Lethal White Syndrome?
Yes, other genetic disorders in horses can lead to similar symptoms, such as Hirschsprung’s disease in humans, which also involves a lack of nerve cells in the intestines. However, lethal white syndrome is unique to horses with the overo coat pattern and the specific EDNRB gene mutation.
Is Lethal White Syndrome Limited to Paint Horses?
While lethal white syndrome is most commonly associated with American Paint Horses, it can also occur in other breeds with the overo coat pattern, such as Quarter Horses and Thoroughbreds. Any breed with the overo pattern may potentially carry the gene responsible for the condition.
Conclusion
Lethal white syndrome is a serious genetic disorder that affects foals born with the overo coat pattern. Although it is a rare condition, understanding its genetic basis and prevalence is crucial for responsible breeding. By utilizing genetic testing and avoiding the mating of two carriers, breeders can significantly reduce the risk of producing affected foals. For more information on genetic testing and breeding practices, consider consulting with a veterinary geneticist or equine specialist.