severe combined immune deficiency can be caused by many different genetic disorders.These defects lead to extreme susceptibility to very serious infections.This condition is considered the most serious of the primary immunodeficiencies.Fortunately, for the treatment of this disorder, there are effective methods, such as bone marrow transplantation and in the future is possible to use gene therapy.
severe combined immune deficiency (SCID), a rare fatal syndrome caused by different genetic factors, and the lack combining functions of T- and B-lymphocytes (and in many cases the lack of function of natural killer cells, or NK-lymphocytes).These defects lead to extreme sensitivity to serious infections.Currently, twelve known genetic causes of SCID.
Despite their difference in specific defects leading to an immune deficiency, some laboratory tests and data types of inheritanc
most common form of SCID, accounting for about 45% of all cases, is caused by mutation of a gene on the X chromosome, encodes a component (or chain), which is available in the growth factor receptorT-cell receptors as well as other growth factors.
This component is referred to as cγ, or common gamma chain.Mutations in this gene result in a very low number of T-lymphocytes and NK-lymphocytes with a large number of B lymphocytes (called T-, B +, NK- phenotype).Despite the large number of B-lymphocytes, their function is not available, since the T-cells can help B-cells to function properly.This disorder is inherited as an X-linked recessive trait.
This type of SCID is only for men, but women can be carriers of the gene and pass it on to each son with a probability of 1 in 2 (50%).
Another type of SCID is caused by mutations of the gene coding for the enzyme adenosine deaminase (ADA).ADA is required for the metabolism of many body cells, especially T cells.
absence of this enzyme leads to the accumulation of toxic products of metabolism of the lymphocytes, whereby the cells are killed.ADA deficiency is the second most common cause of SCID, which accounts for 15% of cases.
Newborns with this type of SCID have the lowest number of all lymphocytes, as well as the very low number of T, B and NK-lymphocyte.This form of SCID is inherited as an autosomal recessive trait.It occurs in both boys and girls.
Another form of SCID is caused by mutations in a gene on chromosome 5 that encodes another growth factor receptor component - the alpha chain of the interleukin 7 receptor (IL-7Rα).
When T, B and NK cells it appears that infants with this type of SCID have B and NK-cells, but no T cells.However, B-cells did not work due to the absence of T cells.Lack of IL-7Rα is the third most common cause of SCID, which accounts for 11% of cases.
This form is inherited as an autosomal recessive trait.It occurs in both boys and girls.
Another type of SCID is caused by mutations in a gene on chromosome 19 that encodes an enzyme lymphocytes Janus kinase 3 (Jak3).This enzyme is required for cγ described above.
When T, B and NK-lymphocytes in infants with this type of SCID is detected picture is very similar to X-linked SCID, iethere are T-, B +, NK-.Since this form of SCID is inherited as an autosomal recessive trait, it affects both boys and girls.
Jak3 deficiency is the cause of at least 10% of cases of SCID.
Three other forms of SCID is caused by mutations in the genes that encode three of the individual protein chains that make up CD3 - another component of the receptor complex of the T cells.
Such mutations in the genes that cause SCID, lead to circuit failure CD3δ, ε ou ζ or.This deficiency is also inherited as autosomal recessive traits.
Another type of SCID is caused by mutations in the gene encoding CD45 - a protein located on the surface of white blood cells and is necessary for T-cell function.This deficiency is also inherited as an autosomal recessive trait.
Four more types of SCID, the molecular causes of which are known, are caused by mutations in genes that encode proteins necessary for the development of the immune recognition receptors on T- and B-lymphocytes.
These include: lack recombinase activating genes 1 and 2 (RAG1 and RAG2) (sometimes referred to as a state of Ommen's syndrome), Artemis deficiency gene deficiency ligase-4.
In young children with these types of SCID is no T- and B-lymphocytes, ie,there is a phenotype T-B-NK +.All these disease are inherited as autosomal recessive traits.
Finally, there may be other mutations that cause SCID, which have not yet identified.
There is another group of genetic disorders of the immune system, leading to combined immune deficiency, which is usually gravity can not be qualified as severe combined immune deficiency.Such violations include bare lymphocyte syndrome (lack of MHC class II of) lack of purine nucleoside phosphorylase (PNP), ZAP70 deficiency, lack of CD25, hypoplasia of the cartilage and hair, lack of MHC class I.
Article courtesy of IPOPI global organization, working to improvethe lives of people with primary immunodeficiency.
Copyright 2007 owned fund Immune Deficiency Foundation, USA."Guidelines for the primary immunodeficiency diseases for patients and their families", from which the material is taken under the license, was developed Immune Deficiency Foundation with support from Baxter Healthcare Corporation.
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