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Price: $45.00Price: £35.00
Breeds: Canadian, Clydesdale, Clydesdale Cross, Clydesdale/Cob, Cob Cross, Cob/Thoroughbred, Cob/Warmblood, Dales Pony, Drum Horse, Fell Pony, Gypsy Cob, Gypsy Cob/Clydesdale, Gypsy Drum Horse, Gypsy Horse, Gypsy Vanner, Irish Cob, Mixed Breed, Tinker Horse, Traditional Gypsy Cob, Unspecified, Welsh Cob
Description
Foal Immunodeficiency Syndrome (FIS), originally known as Fell Pony Syndrome, is a fatal autosomal recessive disorder that primarily affects two relatively rare native UK pony breeds, the Dales and the Fell. FIS is caused by a single variant in the sodium/myo-inositol cotransporter gene SLC5A3, which produces a P446L substitution in the protein. This gene plays a crucial role in the regulatory response to osmotic stress in many tissues, including lymphoid tissue, and the altered protein disrupts both red blood cell production and development of the immune system.
As many as 10% of all Fell ponies born every year are born with FIS, putting a strain on the long-term survival of the breed and increasing the chance of the variant spreading into other breeds. Animal Genetics Inc. has found the variant in approximately 9% of Gypsy horses tested in the US and Europe.
Affected foals appear healthy and normal at birth but begin to show weakness, a dull coat, and anorexia around 2 to 3 weeks of age, as maternal antibodies from colostrum decline. Early clinical signs include diarrhea, nasal discharge, cough, poor growth, pale gums, and decreased appetite, alongside a severe progressive anemia. Foals may initially respond to treatment, but infections persist because the immune system cannot mount its own response. Mortality is 100% despite intensive treatment, and affected foals generally die or are euthanized before three months of age.
Because FIS is recessive, a foal must inherit two copies of the variant to be affected, meaning both parents must be carriers. Carriers have one copy and show no signs of disease. If two carriers are bred, each foal has a 25% chance of being affected and a 50% chance of being a carrier. Since affected foals do not survive to breeding age, every affected foal comes from a carrier-to-carrier mating, so DNA testing of breeding stock is the only way to identify carriers and avoid pairing them.
Animal Genetics offers DNA testing for the FIS variant found in Dales and Fell Ponies as well as any horses with Dales or Fell Pony bloodlines.
Possible results
| Genotype | Description |
|---|---|
| FIS/FIS | Affected: Horse has two copies of the FIS variant and is expected to develop signs of the disorder. |
| N/FIS | Carrier: Horse has one copy of the FIS variant and is not expected to show signs of the disorder. Each offspring has a 50% chance of inheriting the variant. |
| N/N | Clear: Horse does not carry the FIS variant and cannot pass it on to offspring. |
Breeds Affected
Canadian, Clydesdale, Clydesdale Cross, Clydesdale/Cob, Cob Cross, Cob/Thoroughbred, Cob/Warmblood, Dales Pony, Drum Horse, Fell Pony, Gypsy Cob, Gypsy Cob/Clydesdale, Gypsy Drum Horse, Gypsy Horse, Gypsy Vanner, Irish Cob, Tinker Horse, Traditional Gypsy Cob, Welsh Cob
Reference
[PMID: 21750681]