Two years after a genetic test for warmblood fragile foal syndrome (WFFS) was introduced, researchers have used it to document a previously undiagnosed case of the condition.
WFFS, similar to hereditary equine regional dermal asthenia (HERDA), is characterized by severe defects of the skin and other collagen-containing tissues. “Both [conditions] are inherited diseases resulting in offspring with abnormally fragile skin,” says Chloé Monthoux, DVM, of the University of Zurich. In mild cases of HERDA, which may go undiagnosed for several years, the horse’s skin tears under pressure---from tack, for example---or is slow to heal. In WFFS, however, severely affected foals may be born with extensive skin lesions and defects in tendons, ligaments, blood vessels and other structures.
In the WFFS case documented by the Swiss researchers, a mare had been admitted to the university clinic because of a prolonged delivery. When the foal finally arrived, she had extensive skin lesions and an 11-inch-long opening in her abdomen through which her intestines were protruding. Because of the poor prognosis, the filly was euthanatized, and the clinicians collected tissue and blood samples for testing from her and her dam.
The researchers ran a genetic test for HERDA on the samples but it came up negative. A year later, however, the test for WFFS became available, so the dam was retested as were retained tissue samples from the foal. The results showed that the dam was heterozygous, meaning she carried one copy of the mutated gene responsible for WFFS, while the foal was homozygous, meaning she carried two copies of the defective gene---one inherited from each parent.
“To our knowledge, this is the first detailed case description of a homozygous WFFS-positive foal publicly available. Milder cases may [have been] suspected as well as non-observed cases that ended in abortion,” says Monthoux, who adds that she hopes publicity of this case will increase disease awareness and testing practices among breeders.
To develop WFFS, a foal must inherit two copies of the mutated gene. This means that testing breeding stock for the mutation can completely eliminate the risk of having an affected foal. “It is important to notice that carriers (un-affected horses who have only one copy of the gene) do not necessarily need to be excluded from breeding,” says Monthoux. “To avoid affected offspring it is enough to ensure that carriers are not bred to carriers.” She adds that all warmblood horses are candidates for screening, as are any related breeds “with a history of abortion, stillbirth, skin lesions or malformations of the skin in neonates.” For information on testing a horse for WFFS, go to www.animalgenetics.com.
Reference: “Skin malformations in a neonatal foal tested homozygous positive for warmblood fragile foal syndrome,” BMC Veterinary Research, January 2015
This article first appeared in EQUUS issue #453, June 2015.