by Kimberly Allen, RN
Severe combined immunodeficiency disorder, or SCID, is a term used to describe a group of disorders affecting the immune system. It is considered a rare disorder occurring in approximately 1 in 50,000 births. Though it is best known from the 1980’s reports on the little boy David that lived in a plastic bubble there are 14 different types of SCID.
The reason SCID is called a ‘combined’ immunodeficiency is because two types of infection fighting cells are affected, the T-cells and the B-cells. The most common form of SCID is called XSCID because the mutation occurs on the X chromosome in a gene known as SCIDX1. This gene is responsible for a protein that is needed to form the interleukin-2 receptors called IL2RG receptors. These receptors are needed for the T-cells and B-cells to communicate. Without the receptors the T-cells and B-cells are unable to communicate with each other alerting each other when there are ‘invaders’ in your environment. This results in an insufficient number of T-cells and B-cells being produced to fight any infections that may be present. Basically leaving your body defenseless. Because XSCID is a recessive genetic disorder affecting the X chromosome boys are almost always exclusively over girls. Boys have only one X chromosome therefore there’s no back up to take over for the mutated one. Girls on the other hand have two X chromosomes so the second X chromosome is able to fill in and cover for the mutated one. Though girls have the second chromosome to cover, preventing SCID they do still carry the mutated gene becoming carriers and are able to pass that gene onto future generations.
Adenosine deaminase deficiency SCID or ADA SCID is the second most common form of SCID. The ADA protein is considered an essential enzyme that all the cells in your body need to produce DNA. Adenosine deaminase is also needed to breakdown certain toxic metabolites to prevent them from accumulating in your blood stream killing the lymphocytes.
There is another form that manifests exactly like XSCID known as JAK3. JAK3 is a type of protein that is associated with the common Y chain in the interleukin receptors. When this protein is absent it causes the same symptoms as XSCID.
The symptoms of all forms of SCID usually manifest with in the first few months after birth. Regardless of what type of SCID your child may have there are certain symptoms that are common to all. The first being multiple infections. Your infant will have multiple bacterial and viral as well as fungal infections. Also, these infections are generally more serious than in other children and to make matters worse they don’t respond to treatment the way they should. Most infants with SCID also have chronic diarrheah and due to the multiple infections and diarrhea most children also demonstrate failure to thrive.
In the past SCID was considered a fatal disorder. Today is is considered a pediatric emergency. As with all conditions the sooner SCID is diagnosed and your child receives treatment the better the outcome. It’s important that if your body has multiple ear infections, like 8 or more, or infections that don’t resolve after antibiotic treatment and especially if you have a family history of SCID you should talk to your doctor about SCID. Currently the only cure for SCID is a bone marrow or stem cell transplant. The stem cells in bone marrow are able to renew themselves and reproduce continually supplying healthy immune cells. Bone marrow transplants that have the greatest chance of success are those done before your baby is 3 months of age.
There is also research in the area of gene therapy to treat SCID. The scientists at NHGRI as well as others from around the world have been conducting clinical research on ADA SCID as well as other forms of SCID. This research has lead to several breakthroughs in gene therapy including improving the efficiency of gene transfer. They have also made new discoveries regarding the biology of both ADA SCID and XSCID. As research into this rare but once fatal disorder continues there is new hope.
Kimberly Allen is a registered nurse with an AND in nursing. She has worked in ACF, LCF and psychiatric facilities, although she spent most of her career as a home health expert. She is now a regular contributor to HealthAndFitnessTalk.com, dispensing advice and knowledge about medical issues and questions. You can reach her with any comments or questions at firstname.lastname@example.org.