SCID Immune Deficiency
Finds out whether your horse carries the PRKDC variant that causes Severe Combined Immunodeficiency (SCID), an inherited disease of pure...
€43.05 Incl. VAT
About
This test shows whether your horse carries the gene change behind SCID, an inherited condition in which a foal is born without a working immune system and cannot survive.
SCID is a disease of Arabian horses, so any horse with Arabian blood is worth testing, especially before breeding.
Why test?
Breeding. Two carriers can produce an affected foal. Knowing the result of both parents tells you what each mating can produce.
A foal with repeated infections. Its signs look like many common foal infections, so looking at the foal is not enough. The test shows whether SCID is the cause.
Avoiding a costly loss. An affected foal is distressing for the animal and the people caring for it, and costly in lost foals and veterinary expenses.
Clinical signs
Signs appear only in foals that inherited the change from both parents. An affected foal looks healthy at birth, because it is protected by the antibodies it drank in its dam's first milk. Signs appear between two days and eight weeks old, as that borrowed protection fades.
- The foal has almost none of the white blood cells that fight infection and remember it, and makes no antibodies of its own. It does not respond to infection or to vaccination.
- A blood count shows those cells persistently below normal after the first week of life. The other kinds of white blood cell are normal.
- The foal catches infections very easily: fever, breathing problems and diarrhoea
- Infections by organisms that would not trouble a healthy foal, including equine adenovirus, Pneumocystis carinii, Cryptosporidium parvum and many bacteria
- Infections that come back, or never clear up, despite treatment
- After death, the organs that should produce those white blood cells are found severely underdeveloped
Affected foals die in the first months of life, rarely reaching five months, whatever veterinary care is given. Before the DNA test existed, the only certain diagnosis was after death. The diagnosis is made by a veterinarian, combining the history, the examination, laboratory results and this genetic result.
Transmission
SCID is recessive. A foal needs one copy from the sire and one from the dam to be affected. One copy makes a horse a carrier, never a patient. The gene is not on a sex chromosome, so colts and fillies are affected equally.
What each mating can produce:
- n/n x n/n gives 100% n/n
- n/n x n/SCID gives 50% n/n, 50% n/SCID
- n/SCID x n/SCID gives 25% n/n, 50% n/SCID, 25% SCID/SCID
Prevention
There is no treatment, so prevention is a breeding decision.
Breeding. Test breeding stock before mating and never mate two carriers. A carrier mated to a partner that tested negative produces no affected foals.
Keeping valuable lines. Carrying the change is not a reason to leave a horse out of breeding. A carrier stallion with highly desirable traits can be bred to mares that tested negative, and the other way round. Test every foal so the next generation can be planned.
An affected foal. Nothing changes the outcome. Decisions about supportive care and welfare are a matter for your veterinarian.
Results
n/n: negative. No copy of the SCID variant. Cannot pass it on.
n/SCID: carrier. One copy. Healthy, with a normal immune system. Can pass the variant on.
SCID/SCID: affected. Two copies. The foal has SCID.
Sample
Hair roots: 20 to 40 hairs pulled (not cut) from the mane or tail, with the roots attached. Tape them inside the marked area of the printable sample submission form. Hairs without roots cannot be analysed.
Blood: 5 mL of whole blood in a K3-EDTA tube, collected by a veterinarian. Label the tube with the horse's name and send it with the submission form.
Keep samples dry and at room temperature, and do not freeze them. Do not send hair that is wet, mouldy or soiled with bedding or faeces.
Send your sample by regular mail or express delivery to:
Equigerminal Lab HIESE
Rua da Quinta do Sobreiro Nº25
3230-343 Penela, Portugal
Turnaround
Standard processing: results within 5 to 10 working days of the sample arriving at the laboratory. Shipping is arranged and paid for by the client, and transit time is not included in the 5 to 10 working days.
Samples that fail DNA extraction or amplification are repeated at no extra cost, which may add a few working days. We contact you if a new sample is required.
How it works
🛒 Purchase the test: select and buy the test online.
📧 Receive instructions: after payment confirmation you receive sample collection instructions by e-mail.
✨ Collect the sample yourself: pull 20 to 40 hair roots with the bulb attached, or ask your veterinarian to collect blood in a K3-EDTA tube.
📄 Complete the form: print and complete the submission form with the animal identification.
📮 Send it to the laboratory: Equigerminal, S.A., HIESE, Rua da Quinta do Sobreiro, 25, Quinta Vale do Espinhal, 3230-343 Penela, PORTUGAL.
📄 Receive your report: your certified report is issued as soon as the analysis is validated.
FAQs
At what age can a horse be tested?
Any age, from birth. The genotype is fixed at conception and never changes, so one test lasts for life.
Does a negative result rule out immune failure?
No. This test looks for SCID only. It does not detect Cerebellar Abiotrophy, Lavender Foal Syndrome or other inherited immune problems. By far the commonest cause of a foal with no defences is not taking in enough colostrum from its dam.
Is carrying SCID linked to any other problem?
One study found carriers more often among Arabians with sarcoid tumours. No link was found with melanoma.
For Professionals
Genetic and clinical detail for veterinarians, geneticists and laboratories.
- Gene / locus: PRKDC (protein kinase, DNA-activated, catalytic subunit; DNA-PKcs), ECA9.
- Variant: 5-bp deletion causing a frameshift, truncated kinase-negative protein (Shin et al., 1997). HGVS (EquCab3.0): NC_009152.3:g.36395752_36395756del; NM_001163858.1:c.9478_9482del; NP_001157330.1:p.(Asn3160fs*3).
- Alternative designations: OMIA notes that the genomic coordinates were previously listed incorrectly as g.36395752_36395759del (corrected 03/06/2024). Laboratory allele symbol: SCID.
- Variant identifiers: no rs/EVA identifier listed in OMIA; OMIA variant 511.
- Variant classification: not currently evaluated (ISAG/AVCG, per OMIA).
- Discovery: the locus was mapped to ECA9 by linkage to HTG8 and HTG4 (Bailey et al., 1997); the causal deletion was identified by Shin et al. (1997).
- Mechanism: DNA-PKcs carries out the rejoining step of V(D)J recombination, which lymphocytes need to assemble their antigen receptors. Homozygotes lack functional V(D)J recombination (Wiler et al., 1995) and develop no functional adaptive immune system.
- Inheritance: autosomal recessive (OMIA code R; Perryman and Torbeck, 1980).
- Penetrance / expressivity: homozygotes die within the first months of life. Heterozygotes are immunologically normal; carriers were over-represented among Arabians with sarcoids (18.6% of 102) and with tumours overall (13.9%, versus 8.7% of 508 tumour-free Arabians), with no association with melanoma (Ding et al., 2002).
- Breeds with documented carriers or cases: Arabian (OMIA variant record) and part-bred Arabians, including Arab-Barbs and Anglo-Arabs. A SCID phenotype has been reported in a Caspian filly (Larson et al., 2011).
- Allele / carrier frequencies: all figures are carrier frequencies. USA: 8.4% of 250 randomly sampled Arabians (Bernoco and Bailey, 1998); about 8.7% of 508 tumour-free Arabians (Ding et al., 2002). UK: 3/106 (2.8%), national estimate 1 to 5% (Swinburne et al., 1999). South Africa: 6.4% of the 2004/5 purebred Arabian foal crop (n=203) and 3.4% of the 2009/10 crop (n=197), after testing became available (Tarr et al., 2014). Egypt: 0 of 103 horses, including 33 randomly sampled Arabians (AbouEl Ela et al., 2018). Earlier estimates of 25 to 30% came from horses already suspected of carrying the disease and are regarded as far too high. Screening studies have also been published from Morocco, Poland and the wider Middle East and North Africa.
- Clinical / diagnostic notes for veterinarians: in an Arabian foal with recurrent infections, the main differential is failure of passive transfer of colostral immunity, which this test does not assess. LFS foals do not show immunodeficiency.
Key references:
- Shin EK, Perryman LE, Meek K (1997). A kinase-negative mutation of DNA-PKcs in equine SCID results in defective coding and signal joint formation. J Immunol 158:3565-3569. PMID 9103416.
- Wiler R, Leber R, Moore BB, VanDyk LF, Perryman LE, Meek K (1995). Equine severe combined immunodeficiency: a defect in V(D)J recombination and DNA-dependent protein kinase activity. Proc Natl Acad Sci USA 92:11485-11489.
- Bailey E, Reid RC, Skow LC, Mathiason K, Lear TL, McGuire TC (1997). Linkage of the gene for equine combined immunodeficiency disease to microsatellite markers HTG8 and HTG4. Anim Genet 28:268-273.
- Bernoco D, Bailey E (1998). Frequency of the SCID gene among Arabian horses in the USA. Anim Genet 29:41-42.
- Swinburne J, Lockhart L, Scott M, Binns MM (1999). Estimation of the prevalence of severe combined immunodeficiency disease in UK Arab horses as determined by a DNA-based test. Vet Rec 145:22-23.
- Ding Q, Bramble L, Yuzbasiyan-Gurkan V, Bell T, Meek K (2002). DNA-PKcs mutations in dogs and horses: allele frequency and association with neoplasia. Gene 283:263-269. doi:10.1016/s0378-1119(01)00880-0.
- Tarr CJ, Thompson PN, Guthrie AJ, Harper CK (2014). The carrier prevalence of severe combined immunodeficiency, lavender foal syndrome and cerebellar abiotrophy in Arabian horses in South Africa. Equine Vet J 46:512-514. doi:10.1111/evj.12177.
- AbouEl Ela NA, El-Nesr KA, Ahmed HA, Brooks SA (2018). Molecular detection of severe combined immunodeficiency disorder in Arabian horses in Egypt. J Equine Vet Sci 68:55-58. doi:10.1016/j.jevs.2018.05.210.