NK cells, like their name implies, are typically involved in the direct killing of diseased cells. B cells produce antibodies that attack foreign substances such as viruses and bacteria. In addition, some T cells are also able to directly detect and destroy infected or diseased cells. T cells are the helper cells in the blood stream that encourage other cells in the body to respond to foreign substances and combat infections. These defects affect lymphocytes, a type of white blood cells, that become T cells, B cells and natural killer (NK) cells. Severe combined immunodeficiency is a group of hereditary disorders linked to defects of at least 17 different genes. Today, thanks to newborn screening in many states, early intervention, and advances in treatment, children with severe combined immunodeficiency can be successfully treated with bone marrow transplant and in some cases gene therapy. Many died in early childhood after repeated infections. Until a few years ago, the majority of children with severe combined immunodeficiency were not diagnosed until they were at least 6 months old and very sick. At the time, doctors believed the only way to treat children born with this rare disorder was to isolate them until they could receive a bone marrow transplant from related donor with a 100 percent human leucocyte antigen match. Treatment for SCID should be considered a pediatric emergency.Ĭommonly called the “bubble boy disease” or “boy in the bubble” syndrome, SCID became widely known in the 1970s and ’80s due to the publicity and later a movie about David Vetter, a boy with X-linked SCID, who lived in a plastic, germ-free bubble for 12 years. As a result, the child’s body is unable to fight off infections and can become very sick from infections like chickenpox, pneumonia and meningitis and can die within the first year of life. The appropriate planning of breeding of carriers prevents the outcome of affected foals and decreases the incidence of the mutant gene in the population.Severe combined immunodeficiency (SCID) is a group of rare, life-threatening diseases that cause a child to be born with very little or no immune system. The test should be performed in all Arabian and Arabian-crossbred horses used in reproduction. The definitive diagnosis of carriers and affected foals can be done by a DNA test (VetGen, Veterinary Genetic Services, Michigan, USA) of whole blood or cheek swab samples. The mode of inheritance of the genetic defect is an autosomal recessive trait. The DNA-PK enzyme defect results from a deletion mutation of the gene encoding the catalytic subunit. The disease is caused by the lack of activity of the enzyme DNA-dependent protein kinase (DNA-PK), which is required for gene rearrangement of the antigen-receptor on B and T lymphocytes. The poor B and T cell development results in lymphopenia (less than 1,000 cells/uL), marked serum IgM and IgA deficiency, and hypoplasia of lymphoid tissues (thymus, lymph node, spleen, mucosa-associated). This fatal disease was first described in the horse by McGuire and Poppie in 1973. Foals are normal at birth but soon develop fatal infections, particularly when circulating colostrum-derived antibody concentrations become low. adenovirus, coronavirus, Rhodococcus equi, Pneumocystis carinii, and/or Cryptosporidium parvum). This immunodeficiency may occur in Arabian foals (or breeds carrying Arab bloodlines), and manifests clinically by susceptibility to viral, bacterial, fungal, and protozoal organisms (e.g. Severe combined immunodeficiency (SCID) is a fatal condition of both B (humoral) and T (cellular) cell dysfunction.
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