FOAL IMMUNODEFICIENCY SYNDROME (FIS)
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. 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.
POLYSACCHARIDE STORAGE MYOPATHY (PSSM)
Some horses make and store abnormal muscle glycogen and cannot tolerate dietary starches and sugars. Horses with PSSM can be maintained with low-starch and low-sugar rations and precise exercise protocols. In some horses symptoms may begin by 2 to 3 years of age while others can remain subclinical. Clinical signs can include skin twitching, stiffness, firm painful muscles, sweating, weakness, and reluctance to move with light exercise. Occasionally gait abnormalities, mild colic and muscle wasting may also occur. In may cases horse that have tested positive have had no history of 'tying-up' or other symptoms associated with PSSM.
Research conducted at Animal Genetics has identified several additional mutations associated with PSSM1. These DNA mutations form a haplotype that allow us to identify horses with PSSM1. Further ongoing research may provide us with a more comprehensive assay for PSSM and better determine the severity of the disorder in all horses.