UC Davis Center for Equine Health

Warmblood Fragile Foal Syndrome Type 1 (WFFS) is an inherited defect of connective tissue characterized by hyperextensible, abnormally thin, fragile skin and mucous membranes that are subject to open lesions. Affected horses may also have hyperextensible limb joints, floppy ears, accumulation of fluid (hydrops), subcutaneous emphysema, hematomas, and premature birth. The disease is present at birth and affected newborn foals are euthanized shortly after birth due to the poor prognosis of this untreatable condition.

WFFS Type 1 is an autosomal recessive disease, meaning that both males and females are equally affected, and two copies of the mutation are required to cause the disorder. Horses with one copy do not show clinical signs but can transmit the mutation to their offspring. A mutation in the PLOD1 (procollagen-lysine, 2-oxoglutarte 5-dioxygenase1) gene has been associated with WFFS and a DNA test is available to inform breeding decisions and avoid producing affected foals.

Clinical Signs

The clinical signs of WFFS are present from birth and include hyperextensible skin that is abnormally thin and fragile. Friction and pressure points can result in open lesions, often in utero. Affected horses may also exhibit hyperextensible limb joints, floppy ears, hematomas, seromas, hydrops, subcutaneous emphysema, and premature birth. One case report of a confirmed homozygous affected newborn foal described an open abdomen and extensive skin lesions (Monthoux et al. 2015).

Diagnosis

Few cases of WFFS have been described, and clinical signs overlap with other diseases such as hereditary regional dermal asthenia (HERDA). As such, necropsy alone is often insufficient for a definitive diagnosis. The available genetic test may be utilized to confirm a diagnosis of WFFS.

Treatment

Due to the severity of the disease, there is no treatment or cure for WFFS.

Prognosis

Affected foals are unfortunately euthanized shortly after birth. The prognosis for carriers is excellent as there are no known health problems associated with carrier status for this disease. It is possible that homozygosity for the PLOD1 mutation results in early embryonic loss, but additional research is needed to explore this hypothesis.

Prevention

Breeders can prevent WFFS in their horses by performing DNA testing on potential sires and dams and avoiding carrier matings. Hair samples (with the roots attached) can be submitted to the UC Davis Veterinary Genetics Laboratory. Offspring of two WFFS carriers have a 25 percent chance of being affected. Breeding an unaffected horse to a carrier will not result in an affected foal but will produce a WFFS carrier foal 50 percent of the time.

The WFFS genetic test is currently recommended for all Warmblood/Sport Horse populations. The carrier frequency of the WFFS mutation in Warmblood horses is estimated to be 9 to 11 percent. A low carrier frequency of the WFFS mutation has also been identified in Thoroughbreds (1.2 percent). Three cases of WFFS have been reported in Warmbloods and no cases have been reported in other breeds, including Thoroughbreds. The mutation may be present in additional breeds and further investigation is ongoing.

Please note: Updated research indicates Fragile Foal Syndrome is not specific to Warmbloods. Learn more.

Printed with the kind permission of the UC Davis Center for Equine Health. The UC Davis Center for Equine Health is dedicated to advancing the health, welfare, performance and veterinary care of horses through research, education and public service. 

Photo: Dreamstime/Annalie Coetzer