Diagnosis guide · Inherited immune disorders
Severe combined immunodeficiency (SCID)
If you or someone you love has just heard this diagnosis, start here. It covers several subtypes, and this guide shows how they differ, so you can find the one on your report.
SCID is a group of genetic conditions that profoundly impair T-cell immunity. Other immune cells may also be affected, depending on the subtype. Newborn screening can identify a child before symptoms develop. Suspected SCID needs urgent specialist assessment and infection prevention directed by the care team. Donor transplantation is an established treatment for many forms; selected subtypes also have gene-therapy or enzyme-replacement options. The exact genetic cause matters. RAG1 and RAG2 variants, for example, can also cause less severe or later-onset immune disorders; not every variant causes classic SCID.
In short
- SCID is a group of genetic conditions that badly weaken T cells, a key part of the immune system. Newborn screening can find it before symptoms start.
- Each type of SCID has its own genetic cause. The cause matters, because some types can also be treated with gene therapy or enzyme replacement.
- A donor stem cell transplant is an established treatment for many forms of SCID. The cells can come from a relative, an unrelated registry volunteer or cord blood.
8 subtypes
Find the subtype on your report
The exact diagnosis shapes the treatment options. Your care team can explain the name on your report.
ADA-SCID (adenosine deaminase-deficient SCID)
ADA-deficient SCID is a genetic immune disorder in which a missing enzyme allows toxic metabolites to build up, impairing infection-fighting cells. ADA deficiency can also affect organs outside the immune system and can have later-onset forms.
Cell or gene therapy optionsArtemis-deficient SCID (DCLRE1C)
Artemis-deficient SCID is caused by DCLRE1C variants that impair DNA repair needed to build immune-cell receptors. Severe forms lack effective T- and B-cell immunity; partial defects can present differently or later.
Donor transplant optionX-linked severe combined immunodeficiency (X-SCID)
IL2RG-associated SCID disrupts immune signaling needed for T-cell and natural-killer-cell development. B cells may be present but function poorly. Some IL2RG variants cause less typical, later presentations.
Donor transplant optionIL7R-deficient SCID
IL7R-deficient SCID is a genetic disorder that prevents normal T-cell development. B cells and natural-killer cells are typically present, but the lack of effective T-cell immunity leaves a child vulnerable to serious infection.
Donor transplant optionJAK3-deficient SCID
JAK3-deficient SCID is a recessive genetic disorder that disrupts immune signaling. T cells and natural-killer cells are usually profoundly reduced, while B cells may be present but cannot provide normal protection.
Donor transplant optionRAG1 deficiency
RAG1 deficiency impairs the DNA rearrangement needed to build T- and B-cell receptors. Severe loss of function can cause SCID; partial function can cause Omenn syndrome or later combined immunodeficiency with infection and immune dysregulation.
Donor transplant optionRAG2 deficiency
RAG2 deficiency impairs the DNA rearrangement needed to build T- and B-cell receptors. Severe loss of function can cause SCID; partial function can cause Omenn syndrome or later combined immunodeficiency with infection and immune dysregulation.
Donor transplant optionReticular dysgenesis (AK2 deficiency SCID)
Reticular dysgenesis is the most severe form of severe combined immunodeficiency (SCID). Changes in both copies of the AK2 gene leave a newborn with almost no T cells and very few or no neutrophils, the white blood cells that eat bacteria, and usually with hearing loss.
Donor transplant option
For some of these subtypes, a patient needs a donor who is not a relative. The registry that serves your country explains who can join.
Join through NMDPFor people who live in the United StatesLive somewhere else?What to know
Key facts
- U.S. newborn screening
- All 53 U.S. screening programs test for SCIDAll U.S. state and territory newborn screening programs, as of December 2018 (Sheller et al., Frontiers in Immunology, 2020). Source: U.S. newborn screening
- How common
- About 1 in 58,000 newbornsTypical SCID, leaky SCID and Omenn syndrome, 11 U.S. newborn screening programs, 2008–2013 (Kwan et al., JAMA, 2014). Source: How common
- Timing
- Guidelines advise planning it before age 3 monthsEuropean EBMT/ESID inborn errors guidelines, published May 2026, for babies with SCID. Source: Timing
- Gene therapy
- Approved in the EU for ADA-SCID since 2016, when no matched related donor is available; in the U.S. only in clinical trialsEU marketing authorization for Strimvelis, May 26, 2016 (European Medicines Agency); U.S. status as described by Children’s Hospital of Philadelphia, accessed 2026-09-26. Source: Gene therapy
How SCID is diagnosed
In the United States, most babies with SCID are now found by newborn screening. By December 2018, every U.S. newborn screening program tested for SCID. The test uses the dried blood spot collected for other newborn screening tests. It looks for TRECs, small bits of DNA left behind as new T cells form. Very few TRECs can mean a baby is not making T cells.
An abnormal screen is not a diagnosis. The next step is a visit with an immune system specialist (immunologist). Blood tests count the main kinds of immune cells: T cells, B cells and natural killer (NK) cells. Another blood test checks how well the T cells work. If T cells are very low, genetic testing looks for the exact cause. The type of SCID matters, because it can change which treatments fit.
Care teams usually start protecting the baby right away, while tests are still underway. Common steps include keeping the baby away from sick people and skipping live vaccines, such as the rotavirus vaccine. Breastfeeding may pause while the mother is tested for a common virus called CMV. European guidelines updated in 2026 advise starting the donor search while genetic tests are still running, and planning the transplant for before the baby is 3 months old. Before screening, most babies with SCID were found only after infections began, or because of a family history. That can still happen where screening is not done.
A normal newborn screen does not rule out every serious immune disorder. A few related conditions, such as ZAP-70 deficiency, can leave TREC levels normal.
When transplant specialists are usually consulted
NMDP guidance recommends a transplant consultation at diagnosis, or as soon as SCID is detected on newborn screening.
Read the guidanceLooking ahead
Outlook for SCID
Without treatment, SCID is life-threatening. Babies can become very sick from infections such as chickenpox, pneumonia and meningitis, and can die within the first year of life. That is why a positive screen is followed up so quickly.
With treatment, most children now survive, and results have improved over time. In a large study of children transplanted in the United States and Canada, survival was much higher for those transplanted in 2010–2018 than in earlier decades. Babies found by newborn screening did best. Having an active infection at transplant, and being 3.5 months or older at transplant, were both linked with lower survival. Screening helps with both, because it finds babies younger and before they get sick.
The type of SCID also matters. In the same study, babies with SCID caused by DNA-repair problems (such as Artemis deficiency) or by ADA deficiency did less well than babies with X-linked or JAK3 SCID. Survival is not the only measure. Children treated for SCID need lifelong checks of their immune system. Many take antibody (immunoglobulin) replacement and preventive antibiotics until the new immune system is working well.
About these numbers. Each one says which group of people it comes from, and the place and years where the source gives them. It describes what happened across that group, not what will happen to any one person. And a figure measured among people who had a transplant is not the same as the number of people who need one.
- 87%Alive 5 years after transplant
Children with SCID (including leaky SCID and Omenn syndrome) transplanted 2010–2018 at 34 centers in the United States and Canada, Primary Immune Deficiency Treatment Consortium (published 2023); up from about 72–73% for 1982–2009
Read the source: Alive 5 years after transplant - 92.5%Alive 5 years after transplant, babies found by newborn screening
Children with SCID found by newborn screening and transplanted 2010–2018 at 34 centers in the United States and Canada (published 2023); 79.9–85.4% for children found in other ways
Read the source: Alive 5 years after transplant, babies found by newborn screening - 92–100%Alive 5 years after a transplant from a matched brother or sister
Children with any type of SCID transplanted from HLA-matched siblings at 34 centers in the United States and Canada, each time period from 1982 to 2018 (published 2023)
Read the source: Alive 5 years after a transplant from a matched brother or sister
These figures describe children who had a transplant. They are group results and cannot predict how any one child will do.
Common questions
Is SCID the same as “bubble boy disease”?
Yes. “Bubble boy disease” is a nickname for SCID, which became widely known in the 1970s and 1980s. SCID is really a group of rare inherited conditions in which a child is born with very little or no immune system, so a baby cannot fight off infections the way other babies can.
What are the first signs of SCID?
Signs usually show up within the first year of life and generally include repeated infections. In X-linked SCID, the most common form, untreated babies can also have poor growth, ongoing diarrhea, a fungal infection called thrush and skin rashes. Newborn screening can find many babies before any symptoms start. That matters, because the sooner treatment begins, the lower the chance of a dangerous infection.
Is SCID curable?
It can be. For many forms of SCID, a donor stem cell (bone marrow) transplant is an established treatment. It gives the child healthy infection-fighting cells and can cure the condition, though not every child is cured. Some types also have gene therapy or enzyme replacement options. Babies diagnosed in infancy and treated in the first three months of life have the highest success rates.
Can a brother or sister be the bone marrow donor for a child with SCID?
Sometimes. A brother or sister whose tissue type matches offers the greatest chance of a cure, but a matched sibling is often not available. Children’s Hospital of Philadelphia says most of its patients instead receive cells from a parent or an unrelated matched volunteer donor. In large U.S. and Canadian studies, survival after transplant has risen over time, and it is highest in babies found through newborn screening.
Is SCID inherited?
Yes. SCID is a group of genetic conditions, and the pattern depends on which gene is involved. X-linked SCID, the most common form, typically affects boys. Other forms, such as those caused by RAG1 or RAG2 changes, need changes in both copies of a gene and affect boys and girls equally. A genetic counselor can explain what this could mean for future children.
For your next appointment
Severe combined immunodeficiency (SCID)
From the Jada Bascom Foundation disease library, jadabascomfoundation.org. Printed .
Questions to bring to your care team
- Which gene is involved, and does it change the options, such as transplant, gene therapy or enzyme replacement?
- Have brothers and sisters been tissue typed (HLA typed), and has an unrelated donor or cord blood search started?
- Will our baby have chemotherapy before the transplant (conditioning), and why or why not?
- What steps should we take at home until the transplant, for example with visitors, breastfeeding and vaccines?
- What is the exact name of the diagnosis or subtype, and what does it mean for treatment?
- What is the goal of each treatment you are suggesting?
- Is a transplant being considered? Why now, or why not yet?
- Where can our family find support during treatment?
A one-page list to take to the next appointment, with room for notes.
Supporting someone with a diagnosisSupport for patients and families
These independent organizations offer information and support. JBF is not affiliated with them.
- SCID Foundation Shares SCID information, hosts an online family community, and offers Path Forward Scholarships to U.S. families during SCID treatment.United States
- Immune Deficiency Foundation Explains SCID and its types, and works to improve diagnosis, treatment and quality of life for people with primary immunodeficiency.United States
- International Patient Organisation for Primary Immunodeficiencies (IPOPI) International association of national patient groups for primary immunodeficiency, working to improve patients' lives and earlier diagnosis worldwide.Worldwide
Ways to help
Someone may be waiting for a match.
Some people with severe combined immunodeficiency (SCID) are treated with a transplant from a donor. When no relative matches, that donor is often a stranger who joined a registry.
Join the registry
JBF points you to the official registry that serves your country. It explains who can join and what donation involves.
Help someone you love find a donor
If someone you love needs a donor, our family guide explains practical ways to help. A registration drive can add many potential donors at once, for them and for others.
Support this work
Gifts to the Jada Bascom Foundation support donor-awareness education like this page, community outreach, drive planning and referrals to official registries.
Keep learning
Understanding transplant
Short explainers on what a transplant is and what it means for a family.
Sources and further reading
- Inborn Errors of Immunity
EBMT Handbook / NCBI Bookshelf, 2024; accessed September 5, 2026 - Adenosine Deaminase Deficiency
GeneReviews / NCBI Bookshelf, Accessed September 5, 2026 - X-Linked Severe Combined Immunodeficiency
GeneReviews / NCBI Bookshelf, Accessed September 5, 2026 - Severe Combined Immunodeficiency (SCID)
Children's Hospital of Philadelphia, Page undated; accessed 2026-09-24 - X-linked severe combined immunodeficiency
MedlinePlus Genetics (NIH National Library of Medicine), Last updated March 18, 2022; accessed 2026-09-24 - Measuring the effect of newborn screening on survival after haematopoietic cell transplantation for severe combined immunodeficiency: a 36-year longitudinal study
The Lancet (Thakar MS et al., Primary Immune Deficiency Treatment Consortium), July 2023; accessed 2026-09-24 - About Primary Immunodeficiency (PI)
CDC, Last updated April 20, 2026; accessed 2026-09-24 - The Landscape of Severe Combined Immunodeficiency Newborn Screening in the United States in 2020: A Review of Screening Methodologies and Targets, Communication Pathways, and Long-Term Follow-Up Practices
Frontiers in Immunology (Sheller et al.), 2020-10-28 - Newborn screening for severe combined immunodeficiency in 11 screening programs in the United States
JAMA (Kwan et al.), 2014-08-20 - Newborn Screening for Severe Combined Immunodeficiency in the US: Current Status and Approach to Management
International Journal of Neonatal Screening (Dorsey and Puck), 2017-06-21 - Transplant consultation guidelines: Immune deficiency diseases
NMDP, Accessed 2026-09-26 - Updated EBMT/ESID inborn errors working party guidelines for haematopoietic stem cell transplantation for inborn errors of immunity and metabolism
EBMT / Bone Marrow Transplantation (Albert et al.), 2026-05-22 - Strimvelis: EPAR
European Medicines Agency, Authorised 2016-05-26; accessed 2026-09-26
