Severe Combined Immunodeficiency (SCID)
Severe Combined Immunodeficiency Disease (SCID) is an inherited disease seen in pure and part-bred Arab horses. Animals with this inherited condition have an enhanced susceptibility to infection and first show signs of disease at between two days and eight weeks of age. Clinical diagnosis of the disease is not straightforward as the symptoms, such as raised temperature, respiratory complications and diarrhoea, are typical of new-born foals with a range of infections.
Foals affected by SCID always die from the disorder within the first six months of life. This happens regardless of the level of veterinary care. SCID is therefore a distressing condition for the effected animal and the owners or caregivers, and results in financial loss due to dead foals and veterinary expenses.
The disorder is recessive, which means that a horse must be homozygous positive or have two copies of the defective gene to suffer from the disease. Consequently both the sire and the dam must possess at least one copy of the mutated gene in order for the offspring to be afflicted. Offspring born with one copy of the defective gene and one non-defective copy are considered a carrier and have a 50% chance of passing the defective gene on.
A number of studies have attempted to estimate the frequency of SCID carriers in the Arab horse population. Most sources speculate that the percentage of Arab foals which die of SCID is 2-3%. If breeding is random then it would imply that roughly 28-35% of Arab horses are carriers. However, most breeding is rather selective, making the true frequency of carriers in the population somewhat unclear.
Animal Genetics offers DNA testing and detection of the gene mutation responsible for Severe Combined Immunodeficiency (SCID).
Pure and part-bred Arab horses
Additional Tests For Arab Horses:
Animal Genetics has developed a new method for testing horses for Severe Combined Immunodeficiency (SCID). The genetic test verifies the presence of the recessive SCID mutation and presents results as one of the following:
|SCID/SCID||Affected||The horse carries two copies of the SCID gene and is homozygous for SCID. The horse is affected with the SCID genetic disorder.|
|SCID/n||Carrier||Both the normal and SCID alleles were detected. Horse tested heterozygous for SCID and is a carrier of the SCID gene.|
|n/n||Clear||Tested negative for the SCID mutation. Horse can be considered a non-carrier.|