Researchers at the UC Davis School of Veterinary Medicine have published the results of a study that investigated the frequency of the Warmblood Fragile Foal Syndrome (WFFS) mutation in Thoroughbreds. The study demonstrated that the WFFS mutation is not a genetic risk factor for catastrophic breakdown and is only present at a very low frequency in this breed.

Warmblood Fragile Foal Syndrome is inherited in an autosomal recessive fashion, meaning that a horse needs to have two copies of the mutation to be affected. WFFS is a fatal genetic defect of connective tissue characterized by hyperextensible, abnormally thin, fragile skin and mucous membranes. More than 700 Thoroughbreds were tested for the WFFS mutation, including 22 catastrophic breakdown fatalities. The allele frequency among all samples was 1.2 percent and the carrier rate (or horses with one copy) was 2.4 percent. None of the horses in the study had two copies of the mutation and only one of the 22 catastrophic breakdown cases carried the WFFS allele.

The UC Davis Veterinary Genetics Laboratory offers the WFFS genetic test and recommends testing for all Warmblood breeds since the carrier rate in Warmbloods is estimated to be around 9-11 percent. Since the allele was found to be present in the Thoroughbred population, albeit at a low frequency, genetic testing could eliminate the possibility of  breeding two carriers with the potential of producing an affected offspring.

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Bellone, R. , Ocampo, N. , Hughes, S. , Le, V. , Arthur, R. , Finno, C. and Penedo, M. (2019), Warmblood fragile foal syndrome type 1 mutation (PLOD1 c.2032G>A) is not associated with catastrophic breakdown and has a low allele frequency in the Thoroughbred breed. Equine Vet J. Accepted Author Manuscript. doi:10.1111/evj.13182. https://onlinelibrary.wiley.com/doi/abs/10.1111/evj.13182?af=R.

Additional information about WFFS genetic testing is available through the UC Davis Veterinary Genetics Laboratory: https://www.vgl.ucdavis.edu/services/horse/WFFS.php.

UC Davis School of Veterinary Medicine, Statement Regarding the Warmblood Fragile Foal Mutation in Thoroughbreds, April 5, 2019: https://www.vetmed.ucdavis.edu/news/statement-regarding-warmblood-fragile-foal-mutation-thoroughbreds

UC Davis Center for Equine Health, Equine Health Topics database, Warmblood Fragile Foal Syndrome: https://ceh.vetmed.ucdavis.edu/health-topics/warmblood-fragile-foal-syndrome-type-1-wffs

Contacts: Dr. Rebecca Bellone, Director, UC Davis Veterinary Genetics Laboratory, rbellone@ucdavis.edu, (530) 752-9299