First case of Fragile Foal Syndrome in Thoroughbred horses identified

A new collaborative study, conducted by the Royal Veterinary College (RVC), with the University of California Davis Veterinary Genetics Laboratory (VGL) and Rossdales Laboratories, Newmarket has found the first case of Fragile Foal Syndrome (FFS) in a Thoroughbred, a condition previously thought to only be found in warmblood horses.

The disorder is characterised as a connective tissue defect caused by a change in DNA within the procollagen-lysine, 2-oxoglutarate 5-dioxygenase1 (PLOD1) gene. The condition is inherited as an autosomal recessive disorder, which means a foal will only be affected by the disorder if it has two copies of the mutation. Affected foals are typically born with extensive skin lesions due to abnormally thin and fragile skin and, other musculoskeletal abnormalities leading them to be aborted, stillborn or euthanized shortly after birth.

Given its historical association with warmbloods, the condition was called Warmblood Fragile Foal Syndrome (WFFS). However, Dr Rebecca Bellone and her team at VGL, UC Davis recently identified this change in DNA in the PLOD1 gene in other breeds prompting her to approach the RVC Equine Pregnancy Laboratory to screen for the condition in their biobank of clinical cases of pregnancy loss.

Challenging the previous misconception that the disorder was unique to warmblood horses, these findings in a Thoroughbred foal, published in Equine Veterinary Journal, link the same change in DNA in the PLOD1 gene with the same developmental abnormalities described in affected warmblood foals. The outcome is a proposed update of the condition’s name to Fragile Foal Syndrome to reflect these findings and ensure appropriate use of testing methods. The publication also describes the clinical presentation of the condition prior to the delivery of a foal with FFS pointing to the need for new research that focuses on defining diagnostic criteria for FFS prior to pregnancy loss.

The study highlights the importance of genetic testing for FFS in horse breeds that carry the gene mutation to inform breeding decisions and avoid producing affected foals.

Jessica Roach, PhD student at the RVC, said: “Pregnancy loss, stillbirth and neonatal death remain an important source of reproductive losses for horse breeders worldwide. Over the course of my PhD we have collated a large biobank of tissue and data from late term pregnancy losses through the generous co-operation of UK and Ireland TB stud farms and Rossdales Laboratories, Newmarket. This has allowed us to explore the risk factors and pathology of many different causes of abortion and stillbirth. The collaboration with UC Davis and Lexi Grillos provided a fantastic opportunity to explore Fragile Foal Syndrome in our TB population and identify the first TB affected individual. While clearly a distressing condition for affected foals and their owners, the good news is that this lethal syndrome can be avoided with testing and careful mating selection.”