SCID's, severe combined immunodeficiency, is a recessive genetic disorder of Arab and Arab related horses. This disorder results in an incompetent immune system. The foals succumb to infection, usually respiratory, soon after birth. Tough the origin of the gene has not been found, he must have been a popular stallion as the gene is estimated to be relatively common in the Arab. Being a recessive genetic trait, a horse carrying one of the genes appears normal but when a foal is born with two defective genes the result is 100% fatal. Prior to now, there has been little hope for elimination of this problem but now there is an accurate test for the presence of one gene in a horse.

VetGen, L.L.C., has a definitive test for SCID gene in Arabian foals. The test is performed on a mucosal swab or blood. The test can determine if the horse is affected, a carrier, or clear of the gene. PCR restriction enzymes are used to cut up the DNA and the relevant section of the gene is examined. Turn around time is two weeks and the cost is 180 dollars for one horse with significant discounts for more horses. The number is 1 800 483 8436 or visit their site at www.vetgen.com

The rest of this article concerns the probable incidence and a detailed scientific work on the nature of the genetic defect.

Surveys of some populations of arabs have indicated an incidence of death due to SCIDs at around 2.3 percent. Some lines, notably the Polish Arabs, are relatively free of the defect. Surveys in Australia and England found the same two to 3% incidence. Using straightforward math William Jones DVM PhD has calculated that around 25% of the breeding Arabs are carrying (heterozygous) this gene.