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. When a horse is heterozygous for the gene, it is a carrier, but perfectly healthy and has no symptoms at all. Unlike SCID in humans, which can be treated, for horses, to date, the condition remains a fatal disease. The only known form of horse SCID involves mutation in DNA-PKcs. 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 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.

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. Not all forms of SCID have the same cause different genes and modes of inheritance have been implicated in different species.Įquine SCID is an autosomal recessive disorder that affects the Arabian horse. Several forms of SCID occur in animal species. In humans, SCID is colloquially known as 'bubble boy' disease, as victims may require complete clinical isolation to prevent lethal infection from environmental microbes.

The severe combined immunodeficiency (SCID) is a severe immunodeficiency genetic disorder that is characterized by the complete inability of the adaptive immune system to mount, coordinate, and sustain an appropriate immune response, usually due to absent or atypical T and B lymphocytes.

What is the pathology of SCID