Severe combined immunodeficiency (SCID) is a group of inherited immune system disorders caused by a mutation in a gene that affects the immune system. These abnormalities lead to reduced or malfunctioning T- and B- lymphocytes, which are the specialized white blood cells made in the bone marrow that fight off infection. When the immune system is compromised and cannot function properly, it is hard, and sometimes impossible, for the body to battle bacteria and viruses that cause a person to become sick.
SCID gets its name because it affects the function of two kinds of white blood cells, whereas other immune system disorders only involve one. Because it is genetically inherited, the disorder is passed from parent to child. The most common type is caused by a problem in a gene found on the X chromosome and affects only males. Females are carriers, as well, but since they inherit a normal X chromosome too, their bodies can usually fight infections normally.
Babies are protected from infections by immunity transmitted to them by their mothers the minute they’re born; however, over the course of the next several months, they begin to develop their own immune systems and their bodies become responsible for fighting off infections. Sometimes, however, they have immune deficiencies and cannot fight off common infections on their own. SCID is rare, though, and approximately 1 out of 200,000 children are born with it.
There are specific signs doctor’s note when diagnosing SCID. Classic signs include an increased vulnerability to infections. A child who suffers from recurrent bacterial and viral infections that is less responsive to treatment that what would be expected could have immunodeficiency. If a child does show signs of a possible immune disorder, the doctor can perform a blood test to determine the number of white blood cells and test their function. Babies who have this immunodeficiency will have a very low white blood cell count. Parents that are aware of their family’s health history with immunodeficiency can receive genetic counseling and early blood testing to determine whether a child is at high risk for the disease. When it is diagnosed early enough, it will enable early treatment and vastly improve a child’s chance of survival.
The most effective treatment and cure for SCID is a bone marrow or peripheral blood stem cell (PBSC) transplant. Essentially, blood stem cells, which are found in the bone marrow, are introduced into the body in the hopes that the new cells will rebuild the immune system. Typically, the best match donor is a sibling. Each child’s sibling has a 25% chance of being a suitable donor. A parent may also be an acceptable match, but sometimes, a child must rely on a stranger to be their perfect match. The survival rate for children with a matched donor is high, and the likelihood of a good outcome is certainly higher if the transplant is done early, if possible.
There is support for parents who have children with SCID. Always consult with your doctor, and visit http://www.genome.gov/13014325 for more information.
