Severe Combined Immunodeficiency
Right after they're born, babies are partially protected from infections by antibodies transmitted to them by their mothers. (Antibodies are special chemicals made by the body to fight infections.) Within the next few months, though, their immune systems develop and begin to assume responsibility for fighting off infections. But sometimes, babies have immune deficiencies and they don't have the ability to fight off routine infections on their own.
The immune system has many parts. The symptoms of immune deficiency depend on what part of the immune system is affected. Immune deficiencies can range from mild to life-threatening. One example of a life-threatening immune deficiency is severe combined immunodeficiency (SCID). "Combined" means that multiple parts of the immune system are affected.
SCID, an uncommon disease, can be successfully treated if it's identified early; otherwise, it is almost always fatal within the first year of life.
What Is SCID?
SCID is actually a group of inherited disorders that cause severe abnormalities of the immune system. These disorders lead to reduced or malfunctioning T- and B-lymphocytes, the specialized white blood cells made in the bone marrow and the thymus gland to fight infection. When the immune system doesn't function properly, it can be difficult or impossible for it to battle viruses, bacteria, and fungi that cause infections.
SCID is called "combined" immunodeficiency because it affects the function of two kinds of infection-fighting cells. There are 14 forms of SCID. The most common type is caused by a problem in a gene found on the X chromosome and affects only males. Females may be carriers of the condition, but because they also inherit a normal X chromosome, their immune systems can fight infections normally. Males, on the other hand, only have one X chromosome, so if the gene is abnormal the disease appears.
Another form of SCID is caused by a deficiency of an enzyme (adenosine deaminase or ADA), which is necessary for lymphocytes to develop. Other cases of SCID are caused by a variety of other genetic defects.
Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor.
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