Equine Science Update
Reports from the world of  equine research.
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Researchers have identified the genetic mutation responsible for Lavender Foal Syndrome. Lavender Foal Syndrome (LFS), also known as Coat Color Dilution Lethal (CCDL), is a fatal disease of newborn Arabian foals, particularly in those of Egyptian Arabian breeding.

Clinical signs include seizures, nystagmus (involuntary movement of the eyeballs), limb rigidity, paddling movements, and opisthotonus (hyperextension of the head, neck, and spine). The mare often has difficulty giving birth.

The condition derives its name from the abnormal coat colour with which most affected foals are born, variably described as silver sheen, lavender, pale chestnut or pale, dull pinkish grey.
Written by Mark Andrews. Published online 19.06.10
 © Copyright Equine Science Update  2010
Lavender Foal Syndrome
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A team of scientists from Cornell University and the Maxwell H Gluck Equine Research Center have found that Lavender Foal Syndrome is the result of a mutation in a gene called myosin Va (MYO5A).

Lead researcher was Samantha A. Brooks, PhD, assistant professor in the Department of Animal Science at Cornell University's College of Agriculture and Life Sciences.

“The recent completion of the horse genome sequence has provided new tools for mapping traits with unprecedented resolution and power” she explains. “We have applied one such tool, the Equine SNP50 genotyping chip, to a small sample set from horses affected with Lavender Foal Syndrome. A single genetic location associated with the disorder was rapidly identified using this approach.”

All of the affected foals had a single mutation in a specific region (exon 30) in the MYO5A gene.

The myosin Va transport complex is responsible for the transfer of pigment to the keratinocytes and for transport of transmitter substances in the nerve cells. A mutation affecting the gene could easily result in interference with normal function of melanocytes (responsible for hair color) and nerve cells.

The research team went on to design a PCR–based Restriction Fragment Length Polymorphism (PCR–RFLP) assay, which they used to investigate the frequency of the mutant gene. They found that all affected foals tested were homozygous for this mutation (i.e. both copies of the gene were defective).

Of the 14 parents of seven affected foals, eight were available for testing and were found to carry the defective gene.

Carriers, containing one normal and one defective allele, were detected in high frequency in families that had produced an affected foal. Of 23 horses that were related to affected foals, 16 were carriers.

Horses that were not related to affected foals were less likely to be carriers.

“Our results suggest that the population frequency of carriers of this deletion is 10.3% in the Egyptian Arabian” Brooks reports.

She adds that this may be an over estimation “as owners who suspect they have LFS carrying horses may have been more motivated to participate in the study.” On the other hand it could be an underestimate, as some owners might not admit to having had a lavender foal.

“Given our estimate of the number of carriers in the population we expect that around nine LFS foals would be born in the USA each year”

The Arabian has been used to develop other modern light breeds of horses and so it is possible that the LFS allele is also present in those breeds.

“From a practical standpoint, this discovery and the development of a diagnostic test for the LFS allele provides a valuable new tool for breeders seeking to avoid the disease in their foal crop.”

For more details see:

Brooks SA, Gabreski N, Miller D, Brisbin A, Brown HE, et al. (2010) Whole-Genome SNP Association in the Horse: Identification of a Deletion in Myosin Va Responsible for Lavender Foal Syndrome. PLoS Genet 6(4): e1000909. doi:10.1371/journal.pgen.1000909