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Gene or Region: PLOD1
Reference Variant: C
Mutant Variant: T
Affected Breeds: Warmblood and Other Breeds
Research Confidence: High - Findings reproduced multiple studies
Explanation of Results: ffs/ffs = homozygous for Fragile Foal Syndrome, trait expressed ffs/N = heterozygous for Fragile Foal Syndrome, carrier N/N = no variant detected
Fragile Foal Syndrome is a connective tissue disorder resulting in joint laxity and extremely thin skin that is only loosely connected to the body. The skin is easily torn, resulting in lacerations, hematomas, and seromas across the foal. Affected foals are euthanized shortly after birth. As Fragile Foal Syndrome is a recessive disorder, horses must inherit two copies (ffs/ffs) to show the disease. Horses with only one allele (ffs/N) are known as carriers due to their ability to produce affected offspring.
Learn more about Warmblood Fragile Foal Syndrome here.
PLOD1 is an enzyme involved in collagen synthesis. Mutations in mice and humans result in similar connective tissue disorders. The mutation observed in horses alters an amino acid, likely disrupting the function of the encoded protein.
¹ Martin, K., Brooks, S., Vierra, M., Lafayette, W. T., McClure, S., Carpenter, M., & Lafayette, C. (2021). Fragile Foal Syndrome (PLOD1 c.2032G>A) occurs across diverse horse populations. Animal Genetics, 52(1), 137-138. (https://doi.org/10.1111/age.13020)[https://doi.org/10.1111/age.13020]
² Rahael, H., Smythe, M., Dewberry, S., Oberdorfer, A., Allen, K., & Brooks, S. (2023). 44 Detecting conformational differences in Fragile Foal Syndrome carriers utilizing artificial intelligence. Journal of Equine Veterinary Science, 124, 104346. https://doi.org/10.1016/j.jevs.2023.104346
³ Smythe, M., Dewberry, S., Staiger, E., Allen, K., & Brooks, S. (2023). 45 Quantifying gait quality changes in fragile foal syndrome carriers using artificial intelligence. Journal of Equine Veterinary Science, 124, 104347. https://doi.org/10.1016/j.jevs.2023.104347
⁴ Bellone, R. R., Ocampo, N. R., Hughes, S. S., Le, V., Arthur, R., Finno, C. J., & T. Penedo, M. C. (2020). 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 Veterinary Journal, 52(3), 411-414. https://doi.org/10.1111/evj.13182
Monthoux C et al., “Skin malformations in a neonatal foal tested homozygous positive for Warmblood Fragile Foal Syndrome.” (2015) BMC Vet Res. 11: 12. PMID: 256373371.
Equine Recurrent Uveitis (ERU) is the most common cause of blindness in horses, affecting about 3-15% of the horse population worldwide. Characterized by episodes of inflammation of the middle layer of the eye, Equine Recurrent Uveitis in horses leads to the development of cataracts, glaucoma and eventually complete loss of vision.
Foal immunodeficiency syndrome (FIS) is a failure in the development of the adaptive immune system. At 3-6 weeks of age, once the maternal antibodies begin to degrade, foals exhibit signs of anemia, diarrhea, and pneumonia. As these foals fail to respond to treatment for infections, they are humanely euthanized at a young age.
Glanzmann Thrombasthenia (GT) is a blood platelet function disorder, resulting from a reduction in the platelet fibrinogen receptor protein. Clinical signs can be characterized by bleeding on the skin or from the mouth/nostril/gastrointestinal mucosas, and may include skin rashes with blood spots under the skin, nasal bleeding, gastrointestinal and gingival bleedings.
Glycogen Branching Enzyme Deficiency (GBED) is a lethal recessive disorder characterized by seizures, muscle weakness, respiratory failure, and death. Many affected foals do not make it full term and are aborted or stillborn. Carriers (gbed/n) have no known issues.
