Severe immunodeficiency disorder

By: Ethan and Dawsen

Molecular


What chromosomes are involved?

  • This disorder is located on the X chromosome, it is X-Linked recessive.
  • Another form of SCID is caused by a defficiency of the ensyme adenosine deaminase (ADA), which is produced by a gene on chromosome 20.
  • Males are more susceptible to this disorder (X-linked)
  • An X-linked form of SCID (XSCID) was also found in basset hounds, and has similar characteristics to that found in humans.
  • An autosomal recessive variant can be found in other animal species such as dogs, mice, and Arabian horses.

How is the DNA affected? What happens to the gene?


  • A mutation/defect in the T and B cells (T cells notice foreign cells and tell the B cells to attack these foreign cells)
  • Caused by mutations in the gene on the X chromosome called IL2RG.
  • IL2RG is involved in creating the receptors on the surface of a lymphocyte.
  • Because this gene is effected, the receptors don't recognize the foreign cells/matter and they aren't removed from the body.
  • This gene is essentially turned off by the mutation*

Biochemical


How does this mutation affect the function/production of the protein and how does it affect the individual?


  • This disorder effects the gene which is necessary in making receptors which direct lymphocytes to mature and mobilize in order to fight foreign matter.
  • If the lymphocytes aren't directed to mature and move throughout the body, then they cannot protect the body from harmful external matter.
  • This, in turn, then leaves the patient susceptible to viruses such as the common cold, or bacterial infections which wouldn't harm a healthy person.


How can it be spotted?


It can be spotted or noticed when an infant has more infections (such as ear infections and pneumonia) than normal, and if the child isn't reacting to the treatments given. The gene IL2RG on the X chromosome plays a large role in creating the receptors for white blood cells to recognize harmful bacteria, and also helps for the white blood cells to mature and mobilise in order to travel through the blood stream and find the bacteria it is hunting.
http://i.imgur.com/evbANd8.webm

What are symptoms to look for?

Most symptoms will be seen at a very early age, because the child may only live to the age of 3 if not treated.

  • 8 or more ear infections at an early age.
  • 2 or more cases of pneumonia.
  • Infections that don't seem to have any effect from antibiotics.
  • Failure to grow and thrive.
  • A family history of the disease can also effect the likelihood that the child has the disorder well.

Organismal

What happens to the individual due to the genetic issues above? What are the symptoms?

  • The affected individual is more susceptible to a large quantity of infections such as ear infections, lung infections, (pneumonia/bronchitis) and diarrhea.
  • Since the individual is being attacked by so many infections, they have trouble growing.
  • The child will also never gain weight and thrive, and will most likely pass before he/she is 3 years old.

What is the Treatment for SCID?

  • The most common (and effective) treatment for SCID is stem-cell therapy.
  • This therapy includes transplanting stem cells from the bone marrow of a healthy person.
  • These stem-cells will continuously produce a supply of healthy cells and hopefully replace all the unhealthy cells.
  • This procedure is even more effective if the Individual has siblings with matching tissues, and could even cure the SCID.
  • If done within the first three months of life, the treatment will be more successful.

Statistics about SCID

  • While there is no record of babies diagnosed with SCID, the best guess is about 40-100
  • This is a very rare disease, which is good and bad; there aren't many people that get it, but when they do the treatments can be difficult.
  • This disorder is only in babies, because if it isn't treated they die. It doesn't occur in anybody else.
  • SCID is more common in male children due to males having only one X-chromosome, if it occurs in females, it is even more rare.

Did you know?

  • SCID was best known from the news and even a movie created in the 80's about David, the Boy in the Bubble.
  • David was born without a functional immune system, and was placed inside a plastic bubble to prevent him from being affected by bacteria.
  • His "bubble" consisted of what looked to be an astronaut's space walk suit. He had a bubble dome around his head and had oxygen released through the suit.

Works Consulted