As a result, the immune system of the afflicted individual is severely compromised or completely lacking. Immature lymphoid cells of the immune system are particularly sensitive to the toxic effects of these unused substrates, so fail to reach maturity. This means that the substrates for this enzyme accumulate in cells. In another form of SCID, there is a lack of the enzyme adenosine deaminase (ADA), coded for by a gene on chromosome 20. Defective IL receptors and IL receptor pathways prevent the proper development of T-lymphocytes that play a key role in identifying invading agents as well as activating and regulating other cells of the immune system. A mutation in JAK3, located on chromosome 19, can also result in SCID. IL2RG activates an important signalling molecule, JAK3.

X-linked SCID results from a mutation in the interleukin 2 receptor gamma (IL2RG) gene which produces the common gamma chain subunit, a component of several IL receptors.

Though invasive, new treatments such as bone marrow and stem-cell transplantation save as many as 80% of SCID patients.Īll forms of SCID are inherited, with as many as half of SCID cases linked to the X chromosome, passed on by the mother. Without a functional immune system, SCID patients are susceptible to recurrent infections such as pneumonia, meningitis and chicken pox, and can die before the first year of life. The defining feature of SCID, commonly known as 'bubble boy' disease, is a defect in the specialized white blood cells (B- and T-lymphocytes) that defend us from infection by viruses, bacteria and fungi. Severe combined immunodeficiency (SCID) represents a group of rare, sometimes fatal, congenital disorders characterized by little or no immune response.

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