Severe combined immunodeficiency

Infobox_Disease
Name = Severe combined immunodeficiency


Caption =
DiseasesDB = 11978
ICD10 = ICD10|D|81|0|d|80-ICD10|D|81|2|d|80
ICD9 = ICD9|279.2
ICDO =
OMIM =
MedlinePlus =
eMedicineSubj = med
eMedicineTopic = 2214
MeshID = D016511

Severe combined immunodeficiency (SCID), or Boy in the Bubble Syndrome, is a genetic disorder in which both "arms" (B cells and T cells) of the adaptive immune system are crippled, due to a defect in one of several possible genes. SCID is a severe form of heritable immunodeficiency. It is also known as the "bubble boy" disease because its victims are extremely vulnerable to infectious diseases. The most famous case is the boy David Vetter.

Chronic diarrhea, ear infections, recurrent "Pneumocystis jirovecii" pneumonia, and profuse oral candidiasis commonly occur. These babies, if untreated, usually die within 1 year due to severe, recurrent infections. However, treatment options are much improved since David Vetter.

Prevalence

Classical SCID has a reported incidence of about 1 in 65,000 live births in Australia.cite journal |author=Yee A, De Ravin SS, Elliott E, Ziegler JB |title=Severe combined immunodeficiency: A national surveillance study |journal=Pediatr Allergy Immunol |volume= 19|issue= |pages=080130211941085|year=2008 |pmid=18221464 |doi=10.1111/j.1399-3038.2007.00646.x |url=http://www.blackwell-synergy.com/openurl?genre=article&sid=nlm:pubmed&issn=0905-6157&date=2008&volume=&issue=&spage=]

Recent studies indicate that one in every 2,500 children in the Navajo population inherit severe combined immunodeficiency. This condition is a significant cause of illness and death among Navajo children.cite web |url=http://indiancountrynews.net/index.php?option=com_content&task=view&id=2109&Itemid=1 |title=News From Indian Country - A rare and once-baffling disease forces Navajo parents to cope |accessdate=2008-03-01 |format= |work=] Ongoing research reveals a similar genetic pattern among the related Apache people.cite journal |author=Li L, Moshous D, Zhou Y, "et al" |title=A founder mutation in Artemis, an SNM1-like protein, causes SCID in Athabascan-speaking Native Americans |journal=J. Immunol. |volume=168 |issue=12 |pages=6323–9 |year=2002 |pmid=12055248 |doi= |url=http://www.jimmunol.org/cgi/pmidlookup?view=long&pmid=12055248]

Types

Detection

Standard testing of SCID is not currently available for newborns due to the diversity of the genetic defect. Some SCID can be detected by sequencing fetal DNA if a known history of the disease exists. Otherwise, SCID is not detected until about six months of age, usually indicated by recurrent infections. The delay in detection is because newborns carry their mother's antibodies for the first few weeks of life and SCID babies look normal.

Treatment

The most common treatment for SCID is bone marrow transplantation, which has been successful using either a matched donor (a sibling is generally best)or a half-matched donor, who would be either parent. The half-matched type of transplant is called haplo-identical and was perfected by Memorial Sloan Kettering Cancer Center in New York and also Duke University Medical Center which currently does the highest number of these transplants of any center in the world.cite web |url=http://www.merck.com/mmpe/sec13/ch164/ch164l.html |title=Severe Combined Immunodeficiency (SCID): Immunodeficiency Disorders: Merck Manual Professional |accessdate=2008-03-01 |format= |work=] David Vetter, the original "bubble boy", had one of the first transplantations but eventually died because of an unscreened virus, Epstein-Barr (tests were not available at the time), in his newly transplanted bone marrow from his sister. Today, transplants done in the first three months of life have a high success rate. Physicians have also had some success with in utero transplants done before the child is born and also by using cord blood which is rich in stem cells.

More recently gene therapy has been attempted as an alternative to the bone marrow transplant. Transduction of the missing gene to hematopoietic stem cells using viral vectors is being tested in ADA SCID and X-linked SCID. The first gene therapy trials were performed in 1990, with peripheral T cells. In 2000, the first gene therapy "success" resulted in SCID patients with a functional immune system. These trials were stopped when it was discovered that two of ten patients in one trial had developed leukemia resulting from the insertion of the gene-carrying retrovirus near an oncogene. In 2007, four of the ten patients have developed leukemias [ [http://www.esgct.org/downloads/ESGTStatement.pdf Press release] from the European Society of Gene Therapy] . Work is now focusing on correcting the gene without triggering an oncogene. No leukemia cases have yet been seen in trials of ADA-SCID, which does not involve the "gamma c" gene that may be oncogenic when expressed by a retrovirus.

Trial treatments of SCID have been gene therapy's only success; since 1999, gene therapy has restored the immune systems of at least 17 children with two forms (ADA-SCID and X-SCID) of the disorder.

CID in animals

SCID mice are used in disease, vaccine, and transplant research, especially as animal models for testing the safety of new vaccines or therapeutic agents in people with weakened immune systems.

An animal variation of the disease, an autosomal recessive gene with clinical signs similar to the human condition, also affects the Arabian horse. In horses, the condition remains a fatal disease, as the animal inevitably succumbs to an opportunistic infection within the first four to six months of life. [ [http://www.foal.org FOAL.org, an organization promoting research into genetic lethal diseases in horse] ] However, carriers, who themselves are not affected by the disease, can be detected with a DNA test. Thus careful breeding practices can avoid the risk of an affected foal being produced. [ [http://www.vetgen.com/scidref1.html "The New DNA Test for Severe Combined Immunodeficiency (SCID) in Arabian Horses"] ]

Another animal with well-characterized SCID pathology is the dog. There are two known forms, an X-linked SCID in Basset Hounds that has similar ontology to X-SCID in humans [cite journal |author=Henthorn PS, Somberg RL, Fimiani VM, Puck JM, Patterson DF, Felsburg PJ |title=IL-2R gamma gene microdeletion demonstrates that canine X-linked severe combined immunodeficiency is a homologue of the human disease |journal=Genomics |volume=23 |issue=1 |pages=69–74 |year=1994 |pmid=7829104 |doi=10.1006/geno.1994.1460|url=http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WG1-45PMSC1-FK&_user=409397&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000019483&_version=1&_urlVersion=0&_userid=409397&md5=30a567571392ace6f5a8bac4114b2fd5|format=abstract only] , and an autosomal recessive form seen in one line of Jack Russell Terriers that is similar to SCID in Arabian horses and mice.cite journal |author=Perryman LE |title=Molecular pathology of severe combined immunodeficiency in mice, horses, and dogs |journal=Vet. Pathol. |volume=41 |issue=2 |pages=95–100 |year=2004 |pmid=15017021 |doi=10.1354/vp.41-2-95]

References

External links

* [http://www.genome.gov/13014325 Learning About Severe Combined Immunodeficiency (SCID)] NIH
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