Genetic Disorder Research: Severe Combined Immunodeficiency
Spring Valley High School
Biology 1 CP
November 3, 2011

Genetic Disorder Research: Severe Combined Immunodeficiency
Inherited immune disorders are also called primary immune deficiency disorders. They are caused by a mistake in a gene that affects the immune system. Genes carry an inherited code of instructions that tell the body to make all the cells and proteins in the body. Severe Combined Immunodeficiency (SCID) is a group of very rare-and potentially fatal-inherited disorders related to the immune system. This disorder results from a heterogeneous group of genetic conditions. In SCID, there is a fault in the specialized white blood cells (T and B cells) that fight off viruses, bacteria and fungi. The B cells make antibodies that are proteins that attach to unrecognized cells and mark them to be attacked and destroyed. T cells direct B cells to make antibodies against other cells. These cells also direct the rest of the immune system when to attack and also when to stop. They help in the attack as well. SCID is sometimes called “Bubble Boy Disease”. “Bubble Boy Disease” is named after David Vetter, a boy from the 1970’s, who lived in a plastic bubble for 12 years after being diagnosed with SCID. The immune system is supposed to fight off attacks from dangerous bacteria and viruses on a regular basis. However, people with SCID have a problem in their immune system that leaves them defenseless to dangerous infections.
There are many different types of SCID. All forms of SCID are inherited. Some types of SCID appear when the gene is inherited by both parents. These occur in both males and females. Half of the SCID cases are linked to the X chromosome, and is passed on by the mother. The most common form of SCID hasaX-linked pattern of inheritance that’s recessive. It is referred to as X-linked SCID. There is also a mutation in JAK3 on chromosome 19 that can also result in SCID. When a gene is on the X chromosome, males are often more affected than females. Males don’t have a second X chromosome to take place for the defected one. They only need to inherit one bad copy of the gene to have the symptoms of the disorder. Females have two X chromosomes that makes having SCID somewhat ineffective. If one of the X chromosomes becomes defective, there is still a healthy pair left. Females also don’t get symptoms of the disorder, but they will carry the gene and can pass it to their children. Another form of SCID is a lack of the enzyme adenosinedeaminsase(ADA). This is coded for by a gene on chromosome 20. The substrates for this enzyme grow in the cells. Immature lymphoid cells (in the immune system) are sensitive to toxic effects of the unused substrates; they fail to reach maturity. This results in the immune system of the person to be unable to function properly.

About 1 in every 100,000 babies is born with SCID. Doctors can diagnose SCID to the baby before it is born by removing and testing cells from the placenta, or by removing and testing a sample of the fluid surrounding the baby. Symptoms of SCID usually show up in the first few months of their life. Most babies are diagnosed with SCID in the first six months. Infants with SCID tend to appear with infections that are secondary to the lack of T-cell function. The immune system cannot protect the body of a baby, causing babies with this disorder to get one infection after another. Their infections may be frequent, severe, long-lasting or just hard to treat. Some of the bacterial infections may be life-threatening, such as pneumonia, meningitis, and sepsis. Babies also get diarrhea that doesn’t go away. Babies with SCID also don’t gain weight or grow at a normal rate. SCID patients often don’t respond to the medicines used to treat bacterial infections. Unlike people with normal functioning immune systems, people with SCID may suffer more from ear infections, sinus infections, chronic cough, and rashes on skin. It is better to have an early diagnosis of SCID, because without immediate treatment, children with the disease aren’t likely to live past the age two. If a baby starts to show signs of animmune disorder, a doctor can conduct a blood test to count the number of lymphocytes (white blood cells) to test their function. Babies diagnosed with SCID would have a low count of lymphocytes.
Children with SCID must remain cautious and stay away from germ-rich environments where they could pick up a potentially life-threatening infection. Places with large crowds and sick people are things that children with SCID should avoid. Children with SCID should be treated with antibiotics to prevent threatening infections, such as Candidaalbicans(a type of yeast) and Pneumocystis pneumonia (PCP). Patients would be give immune globulin. Immune globulin contains antibodies that would be made by B cells to fight infections, and is usually infused into a vein. Patients also require immune globulin once everythree to four weeks. Each infusion may take from an hour to five hours. These treatments may be given in a doctor’s office, hospital outpatient unit or even at home. Most people do not have side effects from immune globulin, but there are chances of having the chills, headaches, fever,nauseaor chest pain. Fortunately, these can be controlled with medicines or adjustments to the infusion. Furthermore, there are two types of therapy for SCID. Enzyme therapy is a treatment with a form of an ADA enzyme called PEG-ADA. This treatment is about 90% effective in children, but some children still require the immune globulin treatments. The second type of therapy is gene therapy. Gene therapy is still being studied in clinical trials, but this treatment has shown convincing results. However, some children that were treated with gene therapy developed leukemia. There a new trials taking place for gene therapy and still is an experimental treatment for SCID.

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The most effective treatmentand curefor SCID is a bone marrowor cord bloodtransplant. A bone marrow transplant or cord blood transplant replaces the abnormal blood-forming cells and immune system with healthy blood-forming cells from a family member or donor. It can also be from a cord blood unit. Unspecialized stem cells are taken from the bone marrow of a healthy donor and are injected into the SCID patient. The new cells will stimulate the production of the needed immune cells. Transplants done within the first few months of life are the most successful. The tissue from the bone marrow must be matched to the patient; this can limit the usefulness of this therapy. Siblings of patients would make the best donors because their cells are likely to contain a similar genetic type. A gene therapy is not yet made, but may be possible. This therapy would soon compensate for the faulty gene by injecting healthy copies of the gene into a patient’s bone marrow stem cells. A transplant for SCID might not include a high dose chemotherapy. The preparative regimen destroys cells in the bone marrow to make room for the donated cells. Also, it destroys immune cells so they aren’t able to attack the donated cells. Some children with this disorder don’t need a preparative regimen because they already have a low count of immune cells.

In conclusion, Severe Combined Immunodeficiency is agroup of very rare-and potentially fatal-inherited disorders related to the immune system. The disorder causes the immune system to not function properly or even at all. Victims of the disorder will have deadly infections and catch viruses that would put their life in danger. This genetic disorder is a serious disease that can cause infants pain and suffering. This disorder should be treated immediately after being diagnosed. If not treated, results may end in death of a helpless child.
Fischer A. (March 1992) Severe combined immunodeficiencies.ImmunodeficRev.RetrievedMay 5, 2009, from
Genetic Science Learning Center (January 24, 2011) Severe combined immunodeficiency. Learn.Genetics. Retrieved November 3, 2011, from
Myers LA, Patel DD, Puck JM, Buckley RH. (2002) Hematopoietic stem cell transplantation for severe combined immunodeficiency in the neonatal period leads to superior thymic output and improved survival. National Marrow Donor Program. Retrieved 2003 from


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