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Severe Combined Immunodeficiency - SCID - Equigerminal

SCID Severe Combined Immunodeficiency

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DNA test

  • DNA test for the Severe Combined Immunodeficiency (SCID). SCID is an inherited disease seen in pure and part-bred Arab horses.


  • 30 to 40 - hair roots - envelope
  • 5 mL - blood - K3 EDTA tube

Turnaround time

  • 2 to 5  working days

Why test?

  • The DNA test for SCID helps breeders to identify the animals that are carriers of the SCID mutation. This information allows breeders to prevent two carriers from breeding, which reduce the chances of producing an SCID foal.
  • Continued breeding of horses that are carriers of the SCID gene is now possible without the worry of producing SCID foals. For example, carrier stallions that possess highly desirable traits can now be selectively bred to clear (homozygous normal) mares (and vice versa). The resulting foals would have an equal chance of being a carrier or clear of SCID, but would definitely not be affected.
  • The foals could be tested anytime after birth to determine their SCID genotype and future matings could be rationally planned.

Results description

The DNA test verifies the presence recessive SCID mutation and presents results as one of the following:

  • nn Non-carrier of the SCID gene.Tested negative for the SCID mutation.
  • nSCID – Heterozygous horse for SCID gene, both the normal and SCID alleles were detected. The horse is a carrier of SCID genetic disorder and there is a 50% chance this horse will pass a SCID allele to its offspring
  • SCID SCID – Carrier of two copies of the SCID gene. Homozygous horse for SCID mutation. The horse is affected with the SCID genetic disorder.

Additional information

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.