Severe combine Immunodeficiency(SDIC) is an x-linked disease in which the cell's that are involved in immune responses and therefore the immune system itself fail to operate properly. The disease is contracted at birth and is the most serious immunodeficiency disorder among humans. Children that are born with the disease are subject to repetitive severe infections, retarded growth, and even early death.
This chart diagrams the difference between a normal person's immune system and someone with SCID.
Mutations in the IL2RG gene are the cause for SDIC because it is vital in making the protein that produces lymphocytes. These defend the body against possible detrimental invasions such as viruses and infections.
There is actually not a protein that is produced that causes SDIC but it is the lack of a protein that causes a deficiency of lymphocytes in the blood stream.
Discovery of SDIC
The disease was discovered in the 1950's in Switzerland and was the first immunodeficiency disorder that was discovered. This is likely so because of the severity of SDIC.
Although the incidence rate of SDIC is thought to be 1 in 100,000 births in the U.S. and around 1 in 50,000 throughout the world, scientists are still uncertain of these numbers. If the disease is left untreated the child will usually die within a year as a result of persistent infections.
Symptoms of SDIC
Although there can be many signs that a patient has SDIC the most common are frequent infections such as mouth infections, ear infections, pulmonary infections including pneumonia and pneumocystis. In addition to this, the child would begin to lose weight and become very weak, and usually dies of an opportunist infection that takes advantage of the weakened state of the child.
This type of immunodeficiency can be diagnosed by typing the patient's T and B cell's from their blood. Using enzyme labeled antibodies, samples of T cells can be tested; B cells can be tested by using immunoflurescence tests for unique proteins in the blood.
These charts show the difference between the normal counts of T-cells and lymphocytes vs the amount found in a patient with SDIC.
Patients that have SDIC can use antibiotics and immune serum to prevent certain infections but this would not actually cure the disease. Bone marrow transplants within three months of birth have performed with high levels of success. This treatment is regarded as one of the few effective standard treatments for SDIC.
This diagram demonstrates how a bone marrow transplant would take place.
If left untreated, the patient would usually die from SDIC within 2 years of birth from persistent infection. The patient could either undergo a bone marrow transplant but the would most likely have to take antibiotics to help boost the strength of their immune system. These would be taken periodically but would not occupy a lot of time.
The genetic pattern of inheritance is autosomal recessive, about 40% of SDIC cases are inherited from the patients parents.
Originally started in 1990, gene therapy is a treatment that is currently in the experimental stages. The first experiments with peripheral T cells were immediately stopped when patients started to develop leukemia when gene carrying retroviruses were inserted near an oncogene. There have been other experiments done and gene therapy has restored the immune systems of several children, but widespread success has yet to occur.
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Cavazzana-Calvo, Marina, et al. "Gene Therapy of Human Severe Combined Immunodeficiency (SCID)-X1 Disease." Science, vol. 228, no. 5546, 28 Apr. 2000, pp. 669-72. Science, vol. 228, no. 5546, 28 Apr. 2000, pp. 228-5546, science.sciencemag.org/content/288/5466/669. Accessed 1 Feb. 2017. Abstract.
"X-linked SCID." Genetics Home Reference, U.S. National Library of Medecine, Apr. 2016, ghr.nlm.nih.gov/condition/x-linked-severe-combined-immunodeficiency#synonyms. Accessed 5 Feb. 2017.