What is the definition of Severe Combined Immunodeficiency?

Severe combined immunodeficiencies (SCID) are inherited immune system disorders characterized by abnormalities with responses of both T cells and B cells (specific types of white blood cells needed for immune system function). Common signs and symptoms include an increased susceptibility to infections including ear infections; pneumonia or bronchitis; oral thrush; and diarrhea. Due to recurrent infections, children with SCID do not grow and gain weight as expected (failure to thrive). SCID may be caused by mutations in any of several genes and can be inherited in an X-linked recessive (most commonly) or autosomal recessive manner. The most common type of SCID is called X-linked severe combined immunodeficiency (XSCID). Another form of SCID is caused by a deficiency of the enzyme adenosine deaminase (ADA). Infections are treated with specific antibiotic, antifungal, and antiviral agents and administration of intravenous (IV) immunoglobulin. The most effective treatment is transplantation of blood-forming stem cells from the bone marrow of a healthy person.

What are the alternative names for Severe Combined Immunodeficiency?

  • SCID

Is Severe Combined Immunodeficiency an inherited disorder?

SCID can be inherited in an X-linked recessive or autosomal recessive manner depending on the genetic cause of the condition. X-linked SCID is the most common type of SCID and is inherited in an X-linked recessive manner. A genetic disorder is X-linked if the disease-causing gene is on the X chromosome. The X chromosome is one of the two sex chromosomes; females have two X chromosomes and males have one X chromosome and one Y chromosome. In males, one mutated copy of the disease-causing gene causes signs and symptoms of the disorder because they do not have another X chromosome with a working copy of the gene. In females, having one copy of the disease-causing gene would make them a carrier without the genetic disorder; a mutation would have to occur in both copies of the gene to cause the disorder. This is why X-linked recessive disorders, including X-linked SCID, occur much more frequently in males. Because fathers only pass their Y chromosome on to their sons, fathers cannot pass X-linked disorders on to their sons. The other, less common causes of SCID are inherited in an autosomal recessive manner. These types are due to mutations in disease-causing genes on other chromosomes (not the sex chromosomes). In autosomal recessive genetic disorders, a person must have mutations in both copies of the disease-causing gene in order to have signs or symptoms of the disorder. In most cases, the affected person inherits one disease-causing copy of the gene from each of the parents, who are typically carriers with no signs and symptoms of the genetic disorder.
Clinical Trial
  • Status: Recruiting
  • Phase: Phase 1
  • Intervention Type: Drug
  • Participants: 5
  • Start Date: December 21, 2018
Phase I/II Study of Lentiviral Gene Transfer for SCID-X1 With Low Dose Targeted Busulfan
Clinical Trial
  • Status: Recruiting
  • Intervention Type: Procedure
  • Participants: 100
  • Start Date: January 4, 2007
Long Term Follow Up Of Patients Who Have Received Gene Therapy Or Gene Marked Products at St. Jude Children's Research Hospital