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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
Impaired Acrosomal Reaction Subfertility (IAR) causes sub- or infertility in males. In normal fertilization, the the head of a sperm binds to the egg and releases the contents of a structure known as the acrosome. However, some males with IAR are unable to properly carry out this process.
Junctional Epidermolysis Bullosa (JEB), also known as red foot disease or hairless foal syndrome, results in the inability to produce the proteins needed to keep the skin on the body. Affected foals exhibit symptoms within days of birth, including blisters at the pressure points, detatchment of the hooves, and oral ulcers. As there is no treatment, affected foals are humanely euthanized.
Kissing Spines Susceptibility (KSS) evaluates a horses genetic risk for developing Kissing Spines. Horses diagnosed with Kissing Spines will have two or more dorsal spinous processes that are too close together, touch, or even overlap. This bone-on-bone grinding causes varying degrees of pain, and thus decreased mobility.
Lavender foal syndrome (LFS), also known as coat color dilution lethal, is a neurological dysfunction in newborn foals. Symptoms are apparent at birth and include seizures, severe hyper-extension of limbs, neck and back, stiff paddling leg movements, involuntary eye movement and inability to stand or sit upright. The coat usually has a dilute color that ranges in shade from silver to a pale lavender/pink. As there is no treatment, affected foals are humanely euthanized.
