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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.
Occipitoatlantoaxial Malformation 1 (OAAM1) is an inherited developmental condition predominantly found in Arabian horses, characterized by abnormal development of the cervical vertebrae leading to compression of the upper cervical cord and subsequent neurological damage.
Polysaccharide Storage Myopathy (PSSM) is a glycogen storage disorder in which affected horses have chronic episodes of exertional rhabdomyolysis (“tying-up”). Acute symptoms are an unwillingness to move and muscle damage following exercise. Moderate symptoms can usually be managed through a low-sugar/starch diet and exercise.
Recurrent Laryngeal Neuropathy (RLN) is a disease that results in loss of the neurons that open the larynx, significantly affecting performance in Thoroughbreds and other sport horses. It is an important issue for horses in competitive events because the resultant paralysis of the larynx leads to obstruction of air flow during intense exercise, creating the abnormal inspiratory noise that gives RLN its common name: “roaring”.
