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Gene or Region: SLC5A3
Reference Variant: C
Mutant Variant: T
Affected Breeds: Dales Pony and Fell Pony
Research Confidence: High confidence - Findings reproduced in multiple studies
Explanation of Results: fis/fis = homozygous for Foal Immunodeficiency Syndrome, trait expressed fis/n = heterozygous for Foal Immunodeficiency Syndrome, carrier n/n = no variant detected
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. FIS is an autosomal recessive condition, thus a horse must inherit two copies of the allele (fis/fis) to show any signs. Horses with only one copy of the allele (fis/n) are known as carriers due to their ability to produce affected foals.
SLC5A3 is a transporter involved in the response to osmotic stress. There are no known natural variations associated with diseases in any species, though “knock out” mice (which have had the gene experimentally removed) die shortly after birth from hypoventilation. This mutation is a single base substitution that alters an amino acid, likely changing the function of the encoded protein.
Fox-Clipsham LY et al., “Identification of a mutation associated with fatal Foal Immunodeficiency Syndrome in the Fell and Dales pony.” (2011) PLoS Genet. 7: e1002133. PMID: 21750681
Fox-Clipsham LY et al., “Population screening of endangered horse breeds for the foal immunodeficiency syndrome mutation.” (2011) Vet Rec. 169: 655. PMID: 22016514
Tallmadge RL et al., “Fell Pony syndrome: characterization of developmental hematopoiesis failure and associated gene expression profiles.” (2012) Clin Vaccine Immunol. 19: 1054-64. PMID: 22593239
Carter SD et al., “Foal immunodeficiency syndrome: carrier testing has markedly reduced disease incidence.” (2013) Vet Rec. 172: 398. PMID: 23486505
Hereditary Equine Regional Dermal Asthenia (HERDA) is a degenerative skin disease that primarily affects the American Quarter Horse. Loose skin is often an early indication of the disease, and severe seromas, hematomas, ulcerations usually develop around 1.5 years of age. There is no cure, and the majority of affected animals have to be euthanized within 2-4 years.
Hydrocephalus (HDC) is an abnormal build up of cerebral spinal fluid around the brain. It is believed that a narrowed passage within the brain prevents normal fluid absorption, leading to an obvious external cranial distension. Affected foals are often stillborn and are associated with dystocia in the dams.
