Severe Combined Immunodeficiency Disorder
Severe Combined Immunodeficiency (SCID) includes a group of rare but serious, and potentially fatal, inherited immune disorders in which T lymphocytes fail to develop and B lymphocytes are either absent or compromised. Impairment of both B and T cells leads to the term “combined.” Untreated patients develop life-threatening, infections due to bacteria, viruses and fungi. The screening test for T cell receptor excision circles (TRECs), a byproduct of normal T cell development, identifies SCID as well as certain related conditions with low T cells. For example DiGeorge Syndrome with impaired thymus development may cause low T cells and low TRECs. SCID is an autosomal recessive disorder, but can also be inherited as an X-linked disorder, affecting males whose mothers are a carrier for SCID.
Incidence: 1 out of every 50,000 to 100,000 births; however, an exact rate of occurrence cannot be determined until more states are screening newborns for the disease.
Diagnosis: Diagnosis is made by obtaining a CBC with flow cytometry. This testing should be coordinated with Immunology to improve accuracy of ordering and analysis of results. Live vaccines should not be given to a patient with a potential SCID diagnosis until results of follow-up testing are known and are WNL. Therefore, Rotovirus should not be administered in a patient who is currently undergoing a work-up for potential SCID.
Treatment: Bone marrow transplantation provides patients with a functioning immune system that is capable of protecting them from infections. Transplants from sibling matched donors continue to produce the best outcomes, when available. This is still a developing field and as new methods are tested, especially in the newborn population, increasingly better outcomes are being seen even in those without a matched sibling.
False Positives: False positive results are common in premature infants and infants with poor immune systems secondary to illness or other conditions.