Fragile foal syndrome, a genetic disorder previously thought to be found only in Warmblood horses, has been identified for the first time in a Thoroughbred.
The case was identified in a foal in Britain, euthanised because of multiple skin lesions and developmental abnormalities.
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 be affected by the disorder only if it has two copies of the mutation – one from each parent.
Affected foals are typically born with extensive skin lesions due to abnormally thin and fragile skin and other musculoskeletal abnormalities, resulting in them being aborted, stillborn or euthanized shortly after birth.
Investigations were conducted by the Royal Veterinary College, the University of California Davis Veterinary Genetics Laboratory and Rossdales Laboratories in Newmarket, England. A case report has been published in the Equine Veterinary Journal.
Given its historical association with Warmbloods, the condition was called Warmblood Fragile Foal Syndrome.
However, Dr Rebecca Bellone and her team at the Veterinary Genetics Laboratory recently identified this change in DNA in the PLOD1 gene in other breeds, prompting her to approach the Royal Veterinary College’s Equine Pregnancy Laboratory to screen for the condition in its biobank of clinical cases of pregnancy loss.
The affected Thoroughbred foal was found to have the same change in its PLOD1 gene, with the same developmental abnormalities described in affected Warmblood foals.
The researchers have proposed updating the name of the condition to Fragile Foal Syndrome type 1 to reflect these findings.
The case report also describes the clinical presentation of the condition before the delivery of a foal with the syndrome, pointing to the need for new research that focuses on defining diagnostic criteria for the disorder prior to pregnancy loss.
The study highlights the importance of genetic testing for the syndrome in horse breeds that carry the gene mutation in order to assist breeding decisions and avoid producing affected foals.
“Pregnancy loss, stillbirth and neonatal death remain an important source of reproductive losses for horse breeders worldwide,” said Jessica Roach, a PhD student at the Royal Veterinary College.
Over the course of her PhD, a large biobank of tissue and data from late-term pregnancy losses were collated through the co-operation of Thoroughbred stud farms in the UK and Ireland and Rossdales Laboratories. “This has allowed us to explore the risk factors and pathology of many different causes of abortion and stillbirth.”
She said the collaboration with the University of California, Davis, and veterinary student Lexi Grillos, provided a great opportunity to explore Fragile Foal Syndrome in Britain’s Thoroughbred population and identify the first affected individual within the breed.
“Whilst 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.”
A.S. Grillos, J.M. Roach, A.M. de Mestre, A.K. Foote, N.B. Kinglsey, M.J. Mienaltowski, R.R. Bellone. First reported case of fragile foal syndrome type 1 in the Thoroughbred caused by PLOD1 c.2032G>A. Equine Veterinary Journal, online available here https://beva.onlinelibrary.wiley.com/doi/10.1111/evj.13547
The study abstract can be read here.