Lethal white syndrome
Lethal white syndrome is a fatal genetic disorder of foals.
Lethal white syndrome (LWS) is an autosomal genetic disorder most prevalent in the American Paint Horse. Affected foals are born after a full 11-month gestation and appear externally normal, with all-white or nearly all-white coats and blue eyes, but internally have a nonfunctioning colon. Within hours, signs of colic appear, and affected foals die within a few days, often leading to humane euthanasia. The disease is caused by a mutation in the endothelin receptor type B (EDNRB) gene when homozygous, and both parents must be carriers for an affected foal to be born.
Quick Facts
- Symptoms
- Nonfunctioning colon, no meconium, colic, fatal within hours to days
- Onset
- Birth
- Duration
- Hours to days
- Causes
- Homozygous for "frame" allele on endothelin receptor B (EDNRB); Ile to Lys substitution at codon 118.
- Risks
- If both parents are heterozygotes for frame, there is a 25% probability of an affected LWS foal.
- Diagnosis
- Nearly all-white coat at birth, blue eyes, DNA testing, observation for colic, no meconium, pain
- Prevention
- Avoid breeding heterozygous frame horses to each other
- Treatment
- None
Facts from the source article.
Reader's Guide
Lethal white syndrome is significant as a fatal genetic disorder that devastates breeders because foals appear healthy at birth but die painfully within days. It has a similar cause to Hirschsprung's disease in humans, involving a mutation in the EDNRB gene that disrupts neural crest cell migration, affecting both pigment cells and enteric nerve cells. The syndrome highlights the importance of genetic testing, as carriers (heterozygotes) often exhibit a frame overo coat pattern but can be misidentified due to variable expression or masking by other white-spotting genes. The disease has no treatment or cure, and its presence in North American horse populations suggests the mutation occurred early in American history, perhaps in a Spanish-type horse. Accurate identification of carriers through DNA testing is essential to prevent accidental breeding of affected foals.
Did You Know?
- Lethal white syndrome is caused by a mutation in the middle of the EDNRB gene, specifically Ile118Lys.
- Both parents must be carriers of one copy of the LWS allele for an affected foal to be born.
- Carrier horses often exhibit a frame overo coat pattern, but some carriers have minimal or no white markings.
More in Genetic disorders with no OMIM 1-24
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