top of page

Foal Immunodeficiency Syndrome (FIS)

Foal Immunodeficiency Syndrome (FIS)


Gene or region: SLC5A3

Reference allele: C

Mutant allele: T

Affected Breeds: Dales Pony and Fell Pony



Research Confidence:                           High confidence, findings reproduced in multiple studies

What it does:

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


bottom of page