Severe Combined Immunodeficiency
NORD gratefully acknowledges Lisa Vawter, PhD, Medical Writer, and Eric Allenspach, MD, PhD, University of Washington, for assistance in the preparation of this report.
Synonyms of Severe Combined Immunodeficiency
Subdivisions of Severe Combined Immunodeficiency
- leaky or atypical SCID
- typical or classic SCID
- variant SCID
Severe combined immunodeficiency (SCID) is a group of rare congenital syndromes with little or no immune responses. This results in frequent recurring infections with bacteria, fungi, and viruses. Infections that are minor in most people can be life‑threatening in people with SCID.
The immune system includes specialized white blood cells that work together to fight off bacteria, fungi, and viruses. These white blood cells include T lymphocytes (T cells) that are central mediators of the immune response and also directly attack viruses. B lymphocytes (B cells) produce antibodies that attach to invaders and mark them to be destroyed, but they need T cells to work effectively. Natural killer (NK) cells are specialized to help fight viruses as well. Patients with SCID have a genetic defect that affects T cells and at least one other type of immune cell (hence “combined immunodeficiency”).
Types of SCID are classified by which immune cells, T, B, and/or NK cells, are defective. There are several types of SCID, each caused by a different genetic (hereditary) defect. Despite the type of SCID, the primary symptom is reduced or absent immune function and all forms of classic SCID are lethal unless treated appropriately. The type of SCID helps determine the best treatment.
Most states now have newborn screening for SCID to help detect and treat babies prior to them becoming sick. Early detection by newborn screening has dramatically increased the success of the bone marrow transplantation as babies with SCID can avoid early infections.
NORD Member Organizations
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