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Disease Profile

Severe combined immunodeficiency

Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.


US Estimated

Europe Estimated

Age of onset




D81.0 D81.1 D81.2 D81.3 D81.9


Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease.


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype.


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder.


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.


Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable


Other names (AKA)



Congenital and Genetic Diseases; Immune System Diseases; Metabolic disorders;


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).[1] Infections are treated with specific antibiotic, antifungal, and antiviral agents and administration of intravenous (IV) immunoglobulin.[2] The most effective treatment is transplantation of blood-forming stem cells from the bone marrow of a healthy person.[1]


This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

Medical Terms Other Names
Learn More:
80%-99% of people have these symptoms
Chronic diarrhea
Failure to thrive
Faltering weight
Weight faltering

[ more ]

Recurrent respiratory infections
Frequent respiratory infections
Multiple respiratory infections
respiratory infections, recurrent
Susceptibility to respiratory infections

[ more ]

Infection in blood stream
Severe combined immunodeficiency
30%-79% of people have these symptoms
Hair loss
Decreased blood lymphocyte number
Low lymphocyte number

[ more ]

Skin rash
5%-29% of people have these symptoms
Abnormality of the dentition
Abnormal dentition
Abnormal teeth
Dental abnormality

[ more ]

Chronic otitis media
Chronic infections of the middle ear
Enlarged liver
Abnormally small skull
Decreased circumference of cranium
Decreased size of skull
Reduced head circumference
Small head circumference

[ more ]

Recurrent urinary tract infections
Frequent urinary tract infections
Repeated bladder infections
Repeated urinary tract infections
Urinary tract infections
Urinary tract infections, recurrent

[ more ]

Sensorineural hearing impairment
Increased spleen size


A diagnosis of SCID may be suspected if a baby shows any of the following persistent symptoms within the first year of life:[3]

  • Eight or more ear infections
  • Two or more cases of pneumonia
  • Infections that do not resolve with antibiotic treatment for two or more months
  • Failure to gain weight or grow normally
  • Infections that require intravenous (IV) antibiotic treatment
  • Deep-seated infections, such as pneumonia that affects an entire lung or an abscess in the liver
  • Persistent thrush in the mouth or throat
  • A family history of immune deficiency or infant deaths due to infections

A diagnosis can be confirmed by blood tests. Blood tests show significantly lower-than-normal levels of T cells and antibodies.[3]

Since there are other conditions that can result in lower-than-normal numbers of the different types of lymphocytes, the most important tests are those of T-cell function by placing blood lymphocytes in culture tubes, and treating them with various stimulants. Normal T-lymphocytes react to these stimulants by undergoing cell division. In contrast, lymphocytes from patients with SCID usually do not react to these stimuli.

Immunoglobulin levels are usually very low in SCID. Most commonly (but not always), all immunoglobulin classes are depressed (IgG, IgA, IgM and IgE).

The diagnosis of SCID can also be made before the baby is born if there has been another infant in the family with the disorder and if the gene defect has been identified. If genetic analysis had been completed on the infant in the family with SCID, a diagnosis can be determined during subsequent pregnancies. This can be done by molecular testing of cells from a chorionic villous sampling (CVS) or from an amniocentesis, where a small amount of amniotic fluid (which contains fetal cells) is removed.

Early diagnosis, before the infant has had a chance to develop any infections, is very valuable since bone marrow transplants given in the first three months of life have a 94% success rate. In fact, screening newborns to detect SCID soon after birth has been made possible because of recent scientific advances. Approximately half of the babies born in the U.S. are now being screened for SCID.

Testing Resources

  • The Genetic Testing Registry (GTR) provides information about the genetic tests for this condition. The intended audience for the GTR is health care providers and researchers. Patients and consumers with specific questions about a genetic test should contact a health care provider or a genetics professional.

    Newborn Screening

    • An ACTion (ACT) sheet is available for this condition that describes the short-term actions a health professional should follow when an infant has a positive newborn screening result. ACT sheets were developed by experts in collaboration with the American College of Medical Genetics.
    • Baby's First Test is the nation's newborn screening education center for families and providers. This site provides information and resources about screening at the local, state, and national levels and serves as the Clearinghouse for newborn screening information.
    • Bonilla, Francisco A. Development of Population-Based Newborn Screening for Severe Combined Immunodeficiency. Pediatrics 2006;118:S47.


      FDA-Approved Treatments

      The medication(s) listed below have been approved by the Food and Drug Administration (FDA) as orphan products for treatment of this condition. Learn more orphan products.

      • Pegademase bovine(Brand name: Adagen) Manufactured by Lediant Biosciences
        FDA-approved indication: March 1990, pegademase bovine (Adagen) was approved for enzyme replacement therapy for ADA deficiency in patients with severe combined immunodeficiency.
        National Library of Medicine Drug Information Portal
      • Elapegademase-lvlr(Brand name: Revcovi) Manufactured by Leadiant Biosciences, Inc.
        FDA-approved indication: October 2018, elapegademase-lvlr (Revcovi) was approved for the treatment of Adenosine Deaminase-Severe Combined Immunodeficiency (ADA-SCID).


      Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

      Organizations Supporting this Disease

        Organizations Providing General Support

          Learn more

          These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

          Where to Start

          • The American Society of Gene & Cell Therapy provides information on the treatment of immunodeficiency diseases.
          • Genetics Home Reference (GHR) contains information on Severe combined immunodeficiency. This website is maintained by the National Library of Medicine.
          • The National Human Genome Research Institute's (NHGRI) website has an information page on this topic. NHGRI is part of the National Institutes of Health and supports research on the structure and function of the human genome and its role in health and disease.
          • The National Organization for Rare Disorders (NORD) has a report for patients and families about this condition. NORD is a patient advocacy organization for individuals with rare diseases and the organizations that serve them.

            In-Depth Information

            • GeneReviews provides current, expert-authored, peer-reviewed, full-text articles describing the application of genetic testing to the diagnosis, management, and genetic counseling of patients with specific inherited conditions.
            • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
            • The Online Mendelian Inheritance in Man (OMIM) is a catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
            • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
            • PubMed is a searchable database of medical literature and lists journal articles that discuss Severe combined immunodeficiency. Click on the link to view a sample search on this topic.


              1. Learning About Severe Combined Immunodeficiency (SCID). NHGRI. 2014; https://www.genome.gov/13014325.
              2. Hershfield M. Adenosine Deaminase Deficiency. GeneReviews. Mar 2017; https://www.ncbi.nlm.nih.gov/books/NBK1483.
              3. Learning about severe combined immunodeficiency (SCID). National Human Genome Research Institute. July 2010; https://www.genome.gov/13014325.
              4. Severe Combined Immune Deficiency and Combined Immune Deficiency. Immune Deficiency Foundation. 2013; https://primaryimmune.org/about-primary-immunodeficiencies/specific-disease-types/severe-combined-immune-deficiency-and-combined-immune-deficiency/.

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