Written by: Ali Miletic

Learn about the fatal genetic disorder Warmblood Fragile Foal Syndrome.

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Working with foals and providing medical care for them can be one of the most rewarding parts of veterinary medicine. Unfortunately, just like any other species, foals can get sick, which can be very stressful for those involved in breeding and caring for these feisty but vulnerable little creatures.

There is new research being conducted every day to make sure we can give newborn foals the best chance at survival. With the development of genetic testing and genome mapping we are discovering new ways to prevent genetic disorders before the fetus is even created, increasing the likelihood of breeding strong, healthy foals.

For example, in 2007 a gene responsible for Hereditary Equine Regional Dermal Asthenia (HERDA) was identified. HERDA affects certain families of Quarter Horses, particularly in the sport of cutting, and results in hyper-extensible skin, scarring, and severe lesions across the neck and back in both females and males, usually by the age of two. There is no cure and euthanasia is usually the only course of action. There is a diagnostic DNA test for HERDA to allow identification of horses that are carriers to help prevent matings that will result in this specific mutation.

A newly-discovered genetic disorder called Warmblood Fragile Foal Syndrome (WFFS) has been the latest to garner attention. WFFS is an inherited genetic disorder of warmbloods which causes severe skin fragility that ultimately requires euthanasia of the foal. It was first reported in the Journal of Veterinary Research in 2015 regarding a foal born in 2012. This is still a rare condition with very few reported cases, as there appear to be few live births. The syndrome is an autosomal recessive disorder caused by a single mutation in the lysyl hydroxylase 1 (LH1) gene. This gene is also responsible for Ehlers-Danlos Syndrome IV in humans, which causes translucent skin, easy bruising, and severe arterial and digestive problems.

Equine Genetics 101

When egg and sperm meet, genes from both the mother and father’s side create the new genetic makeup of the offspring. There are two basic types of genes present in mammalian genomes: dominant and recessive. Dominant genes (we will use ‘A’ to describe these) behave exactly like they sound. If they are present in the genome, their traits will be prominent. Recessive genes (we will use ‘a’) will take a back seat when paired up with a dominant gene and will only be prevalent if both parents pass on the recessive gene.

Human eye colour is a great way to describe the phenomenon of dominant and recessive genes. Blue eyes are a recessive trait and can only occur when two recessive genes are paired up together (aa). Brown eyes are a dominant trait and can occur when either two dominant genes are inherited (AA), or a dominant and recessive gene is passed along (Aa).

For example, my father has brown eyes and my mother has blue eyes. I inherited the ‘A’ gene from my father, and the ‘a’ gene from my mother, resulting in brown eyes (Aa). My brother, however, has blue eyes (aa), indicating that my father’s genetic makeup for eye colour is also Aa to be able to pass a recessive gene along in order for my brother to have blue eyes. This means Dad is a carrier of the recessive blue-eyed gene even though his eyes are brown. Since my mother has blue eyes, her genetic make up is aa and she can only pass along the recessive gene.

This is the same principle for WFFS. A stallion and a mare would both have to be carriers of, and pass along, a copy of the recessive gene (a 50% chance); in this scenario the foal has a 25% chance of being affected and a 50% chance of being a carrier itself. A completely recessive horse would not live long enough to procreate.

If the affected foal is carried to term, he or she will have very delicate, thin skin that tears or becomes ulcerated from normal contact with its surroundings. These lesions can occur anywhere on the body, but most often occur at pressure points including the hocks, elbows, and fetlocks, which are in contact with the ground when the foal is laying down. Lesions can also be found on oral mucus membranes in the gums and tongue. WFFS foals also have characteristically lax joints, with the fetlocks being the most affected.

What can be done?

Such fragile skin with multiple wounds makes these foals much more susceptible to infection. Their quality of life and overall prognosis is so poor that euthanasia is always the kindest option.

The incidence of carriers of this condition currently sits at about 11%, but a single copy of the gene can be carried through many generations without WFFS being expressed. The availability of genetic testing is still quite new, and this number may change as more widespread testing occurs. Only one laboratory in North America, Animal Genetics Inc. in Tallahassee, FL, has a commercial test available for detecting this recessive gene.

WFFS can be avoided through testing and careful breeding practices. If you are planning to breed your warmblood, speak to your vet. Frozen semen should be tested as well to avoid carrier-to-carrier breeding. In a perfect world, if no carrier of this defective gene is ever allowed to reproduce, it would eventually eradicate the condition from the gene pool