Severe Combined Immunodeficiency (SCID)

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Abstract
Severe combined immunodeficiency (SCID) is a term that describes a broad range of genetic disorders that cause profound defects in the humoral and cellular immune system in humans. Patients that have been diagnosed with SCID usually record a low T cell and natural killer (NK) count in their body. On top of this, patients usually have a high number of B cells, but are usually deficient in specific antibody responses (Allenspach, et al., 2003). SCID can be treated through a bone marrow transplantation (BMT) operation and gene therapy. Patients who do not get treatment usually die in infancy due to infections caused by opportunistic pathogens that are able to thrive in the body due to a weakened immune system. There are two forms of SCID,
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SCID is characterised by the complete loss of immunity that is provided by the T cells as well as reduced functioning of C cells. Every year, the condition affects between 1:50,000 and 1:100,000 newborn babies. According to Rezaei, et al., (2008), the rate of incidence of SCID in newborn babies may be even higher than this due to the number of cases of children who die before doctors can make a positive diagnosis of the disease (Allenspach, et al., 2003). Without a bone marrow transplantation or gene therapy intervention, X-SCID is fatal within the first two years of life. Children who are born by parents without a comprehensive family medical history are usually hospitalized between the ages of six months and three years due to the development of oral candidiasis, recurrent episodes of infections that are caused by opportunistic parasites like Pneumocystis, and failure to develop lymph nodes and tonsils. In addition to this, patients with X-SCID may have rashes, diarrhoea, fever, coughs, and other bacterial infections like pneumonia, and sepsis (Rezaei, et al.,…show more content…
In their paper, Essential Lymphocytophthisis; New Clinical Aspect of Infant Pathology, the authors observed that Swiss infants who were diagnosed with the condition were profoundly lympopenic and would usually die before they reached their second birthday. Subsequent research on this condition was focused on identifying its inheritance patterns. The research identified two main inheritance patterns, namely, an X-linked recessive mode of inheritance and an autosomal recessive mode of inheritance. Giblett were the first to discover the molecular cause of SDIC, adenosine deaminase deficiency, in 1972 (Giblett, et al., 1972). However, it took researchers almost 21 years to determine the second cause of SCID, that is, X-linked SCID (Puck, et al., 1993). Since then, advances in molecular biology have led to a much wider understanding of SDIC and its other causes. It is now known that the disease can be caused by mutations in more than 10 genes in the human body as well as some other causes that have not yet been identified (Russell, et al., 1995). Thus, the gene products of these mutations are components of cytokine receptors like IL-2, IL-4R, IL-7R, IL-9R, IL-15R, and IL-21R. However, mutations of the IL-2RG receptor accounts for more than 46% of all cases of X-linked SCID. Adenosine deaminase deficiency, on the other hand, is responsible for 16% of all SCID cases, while
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