Severe+Combined+Immunodeficiency+(SCID)

= Severe Combined Immunodeficiency (SCID) =

**Describe/Explain the deficiency and its formation:** Severe Combined Immunodeficiency, also known as SCID or “bubble boy disease” is a gene mutation that can be caused by many factors. The most common is XSCID which is caused by mutations in a gene that codes protein the X chromosome known as IL2RG (interleukin 2 receptor gamma gene). This gene plays an important role in sending signals to the molecule JAK3 who in turn transmits information to help the lymphocytes grow and develop. Two types of lymphocytes (white blood cells created in the bone marrow), T and B, are each in charge of a specific immune response, like the protection against unknown infections including bacteria, viruses and fungi. If protein IL2RG or JAK3 have suffered mutations, this process will not complete and the foetus will have a severely compromised or completely lacking immune system.



Another type of SCID is the one caused by a mutation in the gene that encodes a protein/enzyme known as ADA (adenosine deaminase) in chromosome 20. ADA breaks down toxic metabolites/substrates that accumulate to harmful levels and kill lymphocytes and stop their development.

**Explain where this deficiency came from and statistics:** This disease is a gene mutation in both cases I described: the most common is XSCID which is a gene mutation in the X chromosome and the other is the gene mutation in chromosome 20. The way that this genetic disorder is passed on is through inheritance. The percentage of males that get this disease is higher than that of females because males only have one X chromosome and if that is affected then they definitely get the disease. Women, on the other hand, would need to have both their X chromosomes affected to get SCID (both parents had to have the defective gene). Luckily, this deficiency is not very common, as it occurs to 1 out of every 100,000 babies, according to the Genetic Science Learning Center of the University of Utah. **Explain the benefits and limitations of this deficiency:** This disease was known to society in very recent years and became widely known during the 1970s to 1980s due to the case of David Vetter, who had X-linked SCID and was diagnosed with the condition because his older brother had died from it. He lived in a germ-free bubble for almost 13 years before passing away in 1984 after a bone marrow transplant. Ever since this discovery more and more studies have been made to discover more effective ways to deal with this disease, which is a benefit to the people born with SCID after the cure has been discovered: those babies will have luck to have an almost sure cure. The most effective treatment is a stem cell transplant during the first three months of life, otherwise known as a bone marrow transplant in hopes that the new cells will rebuild the immune system, and it has been discovered that the earlier this treatment is started, the most likely it is that the baby will have a normal immune system, so it is recommended to discover if the foetus has the disease when it is in the mother’s womb. However, not all mothers have the financial aid to cover the expenses of the transplant and the scanning of the foetus to see if it has SCId, and this is a limitation amongst society, so not many babies get the opportunity to receive the treatment when it is most effective and usually die because the life expectancy for untreated SCID is the age of 1.

A new treatment that started to flourish in the 1990s and is being further explored to this day is gene therapy. The first FDA-approved gene therapy experiment in the United States was actually for a case of SCID and since its success it has become an alternative way of curing SCID. However, around the year 2000 the trials were stopped due to a negative effect caused by the trial: two girls who had SCID developed a type of leukemia, but it was soon discovered that the mechanism that was used to install the fake gene was flawed and had placed it in another area causing the arousal of a cancer-causing gene (oncogene). This was a limitation to the progress of science towards the finding of a very effective cure for SCID. Nonetheless, this flaw led to scientists being much more careful with the insertion of the gene and find ways to achieve permanent correction of the DNA (in the stem cells) and avoiding the activation of oncogenes (which cause leukemia). Secondly, there is another treatment, though not a cure, specifically for ADA SCID patients: they need to take antibiotics with antibody infusions for protection against diseases and they need to receive ADA injections every week so that the protein completes its function. This disorder is also being explored with gene therapy as a treatment, which could bring scientists to a cure and not just a permanent treatment for the patients.

Finally, there are support groups for people like SCID patients and parents of children with SCID and there was even a conference that united different SCID patients with their own type of SCID so they could talk to some specialized doctors about treatments and about what had worked or not worked for them when they were treated. More of these conferences would be a benefit to society because that is the way problems are solved: by knowing the information from all sides and seeing what works best for what type of the disorder.

**Discuss the following AoI’s associated with your disease/syndrome: social, economic, cultural and ethical.** SCID is, as I explained earlier, widely known since the decade of 1970s. From this date, many tests have been on the run as well as studies and trials on different typed SCID patients. There is a lot of support from the society towards this kind of genetic disorder and genetic scientists are all very active in trying to discover a definite cure for the two most common types of SCID: X-linked and ADA-linked. However, to discover which treatments work on the different types of this disorder, trials have to be organized and run, and that is an ethical issue that has much talk in the world in general. The gene therapy trials started in 1990, ever since the positive treatment of two girls with SCID who are still alive today. After this many other countries aside from the US started to develop more gene therapy trials to help patients with SCID, but as I mentioned earlier, another two girls in the year 2000 were treated with gene therapy and developed leukemia due to the waking of the oncogene. After this, all trials were stopped and there was a debate by people who wanted to keep on doing the trials because they were the path towards discovering the cure for SCID but others said that there could be many other people that suffered like those two girls and got two diseases instead of just one.

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