Severe Combined Immunodeficiency (SCID)

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by ibogart
Last updated 6 years ago

Health & Fitness

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Severe Combined Immunodeficiency (SCID)

SCID is a group of inherited disorders that cause severe immune system abnormalities. These disorders lead to reduced of malfunctioning T and B lymphocytes (the white blood cells made in the bone marrow and thymus gland that fight infection). When the immune system does not function properly, it can be difficult or impossible to fight off viruses, bacteria, and fungi that can cause infection. Because there are numerous types of SCID, it has been discovered and researched over time. It was first described in 1950. Its first molecular cause was discovered in 1972, and its X-linked cause in 1993. SCID occurrs in around 1/58,000 births in both men and women of every race. However, 20% of SCID cases are categorized as X-linked, so males are diagnosed with SCID more frequently than females.

The most effective form of treatment for SCID is a bone marrow transplant to provide the patient with a functioning immune system capable of fighting infections. Enzyme replacement therapy is used to treat ADA SCID by injecting adenosine deaminase into the patient to allow their immune cells to recover from the build up toxins. Gene therapy, an investigational treatment option, has also been used to correct the genetic mutation in their immune cells.



What is it?

1.) X-LINKED SCID: mutation in a gene on the X chromosome called IL2RG. IL2RG is a 4,227 bp long segment that creates part of a receptor on a lymphocyte which when activated leads to figting infections. Most mutations involve changes in one or more nucleotides. More than 300 different mutations on this gene lead to the creation of nonfunctional lymphocytes, which can lead to SCID. Since males only have one X chromosome and IL2RG gene, X-linked SCID is more common for them. 2.) ADA SCID: mutation in the gene that codes for protein adenosine deaminase. It is located on chromosome 20 and is 32,802 bps long. Mutatations occur when a nucleotide is substitued for another. There are 70 known substitutions that cause ADA SCID. ADA protein is an enzyme most active in lymphoctyes that eliminates toxins. When ADA is nonfunctional these toxins build up in the body to levels that are extremely toxic to lymphocytes. ADA SCID is extremely rare and is inhereited in an autosomal recessive pattern.

2 Main Types

Severe Combined Immunodeficiency


The Boy in the Bubble (Fun Fact #2)



Testing & Screening

Children born with SCID lack immune protection, so they are extremely prone to infections. It is diagnosed within the 1st year of life due to the high frequency and severity of infections. Kids with the disorder can become very ill from benign infections and from live viruses present in some vaccines. Without treatment, it is almost always fatal, but with treatment they can live a normal life.

Blood tests done at birth can show low levels of T/B cells and antibodies. By taking notice of the frequency and severity of infections the baby gets, doctors can decide to genetically test the child to see if there are any mutations that would cause SCID. The average age of diagnosis is 6 months. If there is a familial mutation leading to SCID, prenatal screening can be done to sequence the fetal DNA.

Glog by: Isabel Bogart

~FUN FACT #1~There is a significant amount of children with SCID in the Navajo and Apache tribes.


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