LAVENDER FOAL SYNDROME

Heritable disorders are not uncommon in many domestic species, including the horse. Some of these are fatal and of great concern to breeders, not only for the financial loss experienced when producing affected animals but also how this reflects on the breeding program of the stud and the emotional cost to the breeders.
In the Arabian breed, Lavender Foal Syndrome is a disorder that has been known since the 1950’s and usually results in the death of the foal soon after birth. Affected foals display an array of neurological signs - thought to be due to a lesion on the brain - that prevent the foal from standing and nursing normally, and even if not lethal on their own, generally result in the foal being euthanised.

Clinical Signs
Causing pain and suffering, common clinical signs in affected foals are seizures, severe hyperextension of the head, neck, and spinal cord (opisthotonos), stiff, paddling leg movements, and involuntary movement of the eyeballs (nystagmus), but the sign most characteristic of the disorder is the soft lavender colour of the foals’ coats.

The name ‘Lavender Foal Syndrome’ (LFS), comes from the resulting diluted coat colour that lightens the coat hairs and gives the unusual appearance of pale gray, pewter/silver, pale pink and light chestnut, as well as lavender, and is also known ‘Coat Colour Dilution Lethal’ (CCDL). The eye colour may also be grayish-brown or have a bluish tint.

Affected foals display an array of neurological signs that prevent them from standing and nursing normally.

Unfortunately, initial diagnosis can be difficult as the coat colour may not always be present and clinical signs of LFS can easily be confused with a number of neonatal conditions including neonatal maladjustment syndrome, encephalitis or spinal injury.

Relatively rare, the inheritance of Lavender Foal Syndrome is suspected to be recessive, although extensive pedigree analysis has not, to date, been published. Outwardly healthy horses can sire lethally affected foals; therefore a recessive mode of inheritance for LFS is most likely. It is not sex-related and both parents must carry and pass along the mutated allele (gene) for an affected foal to be born.

The majority of documented cases of LFS have been reported in the Egyptian Arabian, a sub-group of the Arabian breed found originally in Egypt but extensively exported and popular in the United States and Australia. It is important to note, however, that LFS has also been reported in other Arabian breeding groups. In the United States Egyptian Arabians have their own registry, although they are also part of the main Arabian studbook, whereas in Australia they are registered with the Arabian Horse Society of Australia - it is estimated that there are 49,000 living registered Egyptian Arabians worldwide. Given that the market for Egyptian Arabian horses particularly values certain popular bloodlines leading to close breeding as owners seek to increase the percentage of this ancestry in their foal crop, this increases the need for vigilant prevention of recessive genetic disorders.

Breakthrough Research
There is no cure for LFS so the only way to avoid wholesale culling of livestock, is if breeders are able to identify which horses may be carriers of the faulty gene. Research into the genetics of LFS has been conducted at the University of California, Davis and Cornell University in the United States, the University of Queensland in Australia and the University of Pretoria in South Africa. In November 2009, Cornell University announced that a DNA test has been developed to detect carriers of LFS, and simultaneously, the University of Pretoria also announced that they had developed a DNA test.

Based on research performed in human medicine and in other animal species, lead researcher Samantha A. Brooks, PhD, an assistant professor from the Department of Animal Science at Cornell University’s College of Agriculture and Life Sciences, and colleagues scanned the entire genome of 36 Egyptian Arabian horses using a newly available technique called a ‘single nucleotide polymorphism (SNP) chip’. Using this genetic chip, the research team identified the MYO5A gene and discovered that a single mutation was present in all tested horses. Further genetic testing found that six of six foals with LFS had two copies of the mutation (i.e., they were homozygous for the MYO5A mutation).

“We also found that 10.3% of the Egyptian Arabian horses unrelated to the foals diagnosed with LFS were carriers of the mutation,” added Brooks. This means that the carrier horses had one copy of the mutant gene, not two.

“The discovery of the gene can be used by breeders to test their horses and avoid carrier-to-carrier matings and thus prevent the birth of affected foals.”

“The discovery of the gene responsible for LFS is very exciting, as it can be used by breeders to test their horses and avoid carrier-to-carrier matings and thus prevent the birth of affected foals,” said Brooks.
The study, “Whole-genome SNP association in the horse: Identification of a deletion in myosin Va responsible for Lavender Foal Syndrome,” is available free online at www.ncbi.nlm.nih.gov.

Researchers are certain that the test, when developed, will be a pivotal tool for breeders seeking to breed within lines segregating for Lavender Foal Syndrome, yet minimise or eliminate the production of affected foals.

Identifying the genetic basis of this condition and developing a diagnostic test for the LFS gene will enable breeders to make more informed selection of mating pairs, thus avoiding the emotional and monetary cost of breeding affected foals and potentially lowering the frequency of this gene in the horse population, without resorting to culling of valuable stock.