Foal Immunodeficiency Syndrome (FIS)

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Foal Immunodeficiency Syndrome (FIS)


Fell Pony syndrome or Foal Immunodeficiency Syndrome (FIS) is a recessive genetic disease that primarily affects two relatively rare native UK pony breeds, the Dales and the Fell pony. FIS is caused by a single mutation in the sodium/myo-inositol cotransporter gene (SLC5A3). This gene plays a vital role in the regulatory response in many tissues including lymphoid tissues. As much as 10% of all Fell ponies born each year suffer from FIS. This has put a strain on the long-term survival of this breed as well as the likely spread of FIS into other breeds. Most recently Animal Genetics has found the mutation that causes FIS in approximately 9% of Gypsy horse breeds in the US and Europe.


Foals must have two copies of the mutated gene in order to be affected with FIS. Therefore, each parent must be a carrier of the mutated gene in order to have an affected foal.  Affected foals appear healthy and normal at birth but begin to show signs of weakness, dull coat and anorexia at 2-3 weeks. The first clinical signs of this disease include diarrhoea, nasal discharge, poor growth, pale gums and decreased appetite. Vision may be affected, presumably due to secondary bacterial infections. Mortality rate for foal affected by FIS is 100% despite intensive treatment. All FIS affected foals generally die or are euthanized before they reach the age of 3 months.

FIS is an autosomal recessive trait, meaning a foal can only be affected if the foal inherits the disease from both parents. Parents that are carriers do not have any symptoms associated with FIS. However, they will pass on a copy of the defective gene to their offspring 50% of the time.

Animal Genetics offers DNA testing for both the FIS mutation found in Dale and Fell Pony as well as any horses with Dale and Fell Pony blood lines.

Breeds Affected:

Dale Pony, Fell Pony and Gypsy horse breeds well as any horses having Dale and or Fell Pony blood lines.

Test Results:

Animal Genetics offers DNA testing for Foal Immunodeficiency Syndrome (FIS). The genetic test verifies the presence of the mutated SLC5A3 Gene and presents results as one of the following:

Foal Immunodeficiency Syndrome (FIS):

FIS/FIS Affected The horse carries two copies of the mutated gene and is homozygous for FIS. The horse is affected with the FIS genetic disorder associated with your breed.
n/FIS Carrier Both the normal and mutated alleles were detected. Horse tested heterozygous for FIS and is a carrier of the FIS mutation associated with your breed.
n/n Clear Horse tested negative for FIS and does not carry the FIS gene mutation. The horse will not pass on the defective gene to its offspring.

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