Ariaban Essence

SCID
By Giovanna Romano

Equine SCID is a congenital disorder that affects the Arabian horse. Similar to the "bubble boy" condition in humans, an affected foal is born with no immune system, and thus generally dies of an opportunistic infection, usually within the first four to six months of life.


SCID has been of grave concern to Arabian horse breeders for the past several decades. It is inherited as an autosomal recessive disease, which means that one copy of the disease gene is inherited from a carrier stallion and another from a carrier mare. The foal which inherits two copies of the disease gene is affected with a lethal inability to fight infections, and dies within the first few months of life.




                                                                                                                             Photo: Gigi Grasso


SCID is one of six genetic diseases known to affect horses of Arabian bloodlines, and the only one of the six for which there is a DNA test to determine if a given horse is a carrier of the allele. There are other genetic diseases that affect other horse breeds,and horses of part-Arabian bloodlines can be carriers of SCID. Studies from a little less than 20 years ago indicated that the frequency of affected Arabian foals was around 3%. This places the carrier frequency at about 28% and means that one out of every three or four adult Arabian horses is carrying the gene for this deadly disease. Another way of stating this is that 7-10% of all matings are between carriers, and thus this proportion of matings is at risk to produce a foal that will soon die from SCID.




                                                                                                                             Photo: Gigi Grasso

Unlike SCID in humans, which can be treated, for horses, to date, the condition remains a fatal disease. When a horse is heterozygous for the gene, it is a carrier, but perfectly healthy and has no symptoms at all. If two carriers are bred together, however, classic Mendelian genetics indicate that there is a 50% chance of any given mating producing a foal that is a carrier heterozygous for the gene, and a 25% risk of producing a foal affected by the disease. If a horse is found to carry the gene, the breeder can choose to geld a male or spay a female horse so that they cannot reproduce, or they can choose to breed the known carrier only to horses that have been tested and found to be "clear" of the gene. In either case, careful breeding practices can avoid ever producing an SCID-affected foal.


There is a DNA test that can detect healthy horses who are carriers of the gene causing SCID, thus testing and careful, planned matings can now eliminate the possibility of an affected foal ever being born.



                                                                                                                             Photo: Gigi Grasso

In fact the discovery of the genetic cause of SCID in Arabian horses has been achieved through the collaborative efforts of Dr. Lance Perryman and Dr. Katherine Meek at North Carolina State University and at the University of Texas Southwestern Medical Center at Dallas. VetGen LLC, an Ann Arbor, Michigan-based veterinary genetic testing company, has licensed the technology for the detection of this mutation.



About the Author

Giovanna Romano Go to the author's page

Graduated from the Veterinary School of Turin University with a Degree Thesis on “Diagnostic Ultrasonography on the Reproductive Tract of the Mare” in July 1989.  November 1989, admission to National Board of Veterinarian  REG.NO.To1157.

November 2002,Vienna, ECAR Diploma (European College of Animal Reproduction, Equine sub-speciality) January 2005: Member of ECAR Credential Committee.

Our centre is accredited as “ECAR training center” and can support the training for Ecar residents.

February 2011: member the EAEVE list of experts. EAEVE is a European Association in charge of quality evaluation of accredited veterinary faculties according to high standards.

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