Severe combined immunodeficiency

Severe combined immunodeficiency (SCID), sometimes referred to as 'bubble boy disease,' is a group of rare, life-threatening genetic disorders characterized by profound deficiencies in both T-lymphocyte and B-lymphocyte function, resulting in a severely compromised immune system. SCID can be caused by mutations in numerous genes, including IL2RG (the most common X-linked form), JAK3, IL7R, RAG1, RAG2, DCLRE1C (Artemis), ADA, and others. The condition primarily affects the immune system, leaving affected infants extremely vulnerable to severe, recurrent, and opportunistic infections involving the lungs, skin, and gastrointestinal tract. Infants with SCID typically present within the first few months of life with persistent diarrhea, failure to thrive, chronic skin rashes, oral thrush (candidiasis), and recurrent severe infections caused by bacteria, viruses, and fungi. Without treatment, SCID is almost universally fatal within the first one to two years of life. Affected infants characteristically have absent or very low T-cell counts, and lymphocyte function is severely impaired. Many newborn screening programs now include SCID detection through T-cell receptor excision circle (TREC) assays, enabling earlier diagnosis. The standard of care and most effective treatment for SCID is hematopoietic stem cell transplantation (HSCT), ideally performed as early as possible and preferably from an HLA-matched sibling donor. Outcomes are significantly better when transplantation occurs before the onset of severe infections. For adenosine deaminase (ADA)-deficient SCID, enzyme replacement therapy with pegylated ADA (PEG-ADA) is available as a bridging treatment. Gene therapy has emerged as a promising therapeutic option, particularly for X-linked SCID and ADA-SCID, with several clinical trials demonstrating durable immune reconstitution. Supportive care includes infection prophylaxis, immunoglobulin replacement, and protective isolation until definitive treatment restores immune function.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

Common questions about Severe combined immunodeficiency