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Severe Combined Immunodeficiency (SCID)

  • Severe Combined Immunodeficiency (SCID)

    The rare genetic disorder severe combined immunodeficiency (SCID)—popularized in the 1976 movie “The Boy in the Plastic Bubble”—is actually a group of several different diseases. There are more than 10 documented types of SCID, all of which:

    • are present at birth
    • involve missing T cells (white blood cells that identify and attack perceived “invaders”)
    • affect the function of the B cells (white blood cells that produce antibodies against infection)

    Because SCID all but eliminates a child’s immune system—the body’s built-in defense against infection—children with SCID are at high risk of developing severe infections.

    Although SCID remains a very serious illness, treatment options have come a long way since the debut of “The Boy in the Plastic Bubble.” New approaches in diagnosing and managing the disorder are providing new hope for children and families.

    How Boston Children's Hospital approaches SCID

    Boston Children’s has a long history of caring for children with complex disorders of the immune system. Clinicians in our Division of Allergy and Immunology are international leaders in understanding and treating rare conditions like SCID.

    Most children with SCID receive a stem cell transplant (also known as a bone marrow transplant), so that they can develop new white blood cells, replenishing their immune systems. The Dana-Farber/Boston Children's Cancer and Blood Disorders Center's Stem Cell Transplant Centerone of the first pediatric transplant centers in the nation—performs more than 90 stem cell transplants each year.

    In addition, Boston Children’s is helping to lead an international gene therapy trial for SCID. The trial—which transplants genetically modified stem cells from a child’s own bone marrow—may signify a promising new approach to fighting and defeating the disease.

    SCID: Reviewed by Francisco Bonilla, MD, and Luigi Notarangelo, MD.
    © Boston Children's Hospital; posted in 2014

  • Severe combined immunodeficiency (SCID) is very rare, affecting between 50 and 100 children born in the U.S. every year. Because it is a genetic disorder (caused by an error in the genes), in affected children, the condition is present at birth.

    Essentially, children with SCID lack the ability to produce an immune system. The human immune system constantly patrols, protects and defends the body from all types of “enemies,” including:

    • bacteria
    • viruses
    • parasites
    • fungi

    The immune system first takes root in a developing fetus’ bone marrow. That’s where some stem cells eventually mature into the two cell types that play the biggest role in warding off infection: T cells (white blood cells that identify and attack perceived “invaders”) and B cells (white blood cells that produce antibodies against infection).

    A child with severe combined immunodeficiency (SCID):

    • cannot produce T cells
    • does not have working B cells (because there are no T cells for them to work with)
    • has virtually no immune system

    Without a functioning immune system, a child with SCID has no way of warding off infections. From the time she is born, she will be at constant risk for:

    • pneumonia
    • chronic diarrhea
    • thrush infections of the mouth and skin
    • many other types of infection, including severe viral infections and invasive bacterial or fungal infections

    While a child's specific course of treatment depends on her individual symptoms and circumstances, nearly every child with SCID undergoes stem cell transplant (also known as a bone marrow transplant). Because stem cells have the special ability to develop into other types of cells, a transplant will give the child’s body an essential new source of healthy white blood cells—rebuilding his immune system and allowing him to successfully ward off infections.

    Causes

    What causes SCID?
    There are more than 15 recognized kinds of SCID, but the most common type, known as SCID-X1 (for “X-linked severe combined immunodeficiency”), involves a defect in a gene on the X chromosome. Because girls have two X chromosomes while boys have only one, SCID-X1 affects only male children. However, girls can be “carriers” and can pass the disorder on to their own sons later in life.

    Different genetic defects cause each form of SCID. But all types of SCID are genetic—meaning they are caused by an error or mutation in the child’s genes.

    Even though SCID is a genetic condition, having one child with SCID does not necessarily mean other family members, including siblings, are going to develop the disease. However, it is a good idea to ask your doctor about genetic counseling for you and your other children.

    Signs and symptoms

    What are the symptoms of SCID?
    SCID can be difficult to detect because babies with the disorder may not show any signs of illness until they develop a telltale infection. In most cases, infections are the first indication that a child may have SCID, though in some children the first sign is a failure to thrive.

    One Patient's Story
    Meet Agustin, who has new hope for a healthy tomorrow thanks to a new, landmark study at Boston Children’s 

  • How is SCID diagnosed?

    A diagnosis of severe combined immunodeficiency (SCID) is usually based on a complete medical history and physical examination of your child. In addition, multiple blood tests—including a complete blood cell count—may be ordered to help confirm the diagnosis. The Division of Allergy and Immunology at Boston Children's Hospital is one of the world's leading centers in the diagnosis and treatment of SCID.

    Newborn screening also plays an important role in detecting SCID before symptoms emerge. A growing number of states test for SCID as part of a mandated newborn screening process. Having a screening performed is especially important, because many infants with SCID show no signs until they actually develop an infection.

    Screening does have its limitations. A positive result for SCID on a newborn screen is not the same as a conclusive diagnosis, and screening does not catch all children with SCID and SCID variants. However, it is an important means by which children who may have SCID can be detected early.

  • What are the treatment options for SCID?

    Guarding against infection
    Nothing is more important to the health of a child with severe combined immunodeficiency (SCID) than warding off potential infections. Your child's clinician can advise you about the exact steps you should be taking to help reduce the risk of infection.

    Mothers of newborn children with SCID should discuss the pros and cons of breastfeeding with their clinicians, as some infections can be passed through breast milk.

    As a rule, children with SCID should not receive the standard childhood vaccinations. Because the B cells of children with SCID do not function properly, their bodies cannot produce the normal antibodies that fight off viruses. Since many vaccines are actually live viruses, they pose too high a risk of infection to be safe for a child with a drastically weakened immune system.

    Other ways to avoid potential infections include:

    Basic precautions

    You should be sure to always:

    • keep your child away from crowds, dirty places or anyone who is ill or seems to be "coming down with something"
    • follow a strict hand washing regimen for your child, your family and any visitors
    • use protective face masks at the recommendation of your child's doctor
    • give your child antibiotics, antifungal or antiviral medications at the direction of your child's doctor

    Antibody infusions
    Because your child's body does not have healthy B cells that produce antibodies against infection, he may need regular intravenous (IV, administration through a vein) or subcutaneous infusions (administration under the skin) of the antibody immunoglobin (also known as immune globin, gammaglobin, IVIG or SCIG).

    Stem cell/bone marrow transplants
    Nearly every child with SCID is treated with a stem cell transplant (also known as a bone marrow transplant). This is the only available treatment option that has a chance of providing a permanent cure. The bone marrow cells or stem cells are administered through an IV, similar to a blood transfusion.

    Stem cells are a versatile type of cell found in bone marrow. These cells have a unique and powerful ability: they can develop into several different types of specialized cells.

    In the case of a child with SCID, the transplanted stem cells are injected into the bloodstream. They will then become healthy white blood cells that replenish immune functions—essentially building a whole new, functional immune system for the child. If the immune system regains complete function, the child may be permanently cured.

    The effectiveness of a stem cell transplant for SCID depends on:

    • your child's overall health at the time of the procedure
    • the match between your child and donor's bone marrow (if the donated marrow comes from a matched sibling, the procedure has a better than 90 percent success rate)
    • your child's age at the time of the transplant (For optimal success, a baby should have the transplant performed no later than the age of 3 months; some studies have shown that, if stem cell transplants are performed within the first 28 days of a baby's life, the success rate is as high as 95 percent.)

    There can be some obstacles to a successful stem cell transplant. For instance, a suitable donor may not be available.

    In addition, any transplant carries a risk of a phenomenon known as graft-versus-host disease. This means that the donated bone marrow attacks the recipient, which can be a fatal complication.

    At Boston Children's Hospital, stem cell transplants are conducted through the Stem Cell Transplant Center at Dana-Farber/Boston Children's Cancer and Blood Disorders Center.

    Gene therapy
    A promising field, gene therapy, may have the answers to the obstacles that are present with stem cell transplants. In gene therapy, patients receive stem cells from their own bone marrow (rather than from another person). These cells also have an added ingredient: they've been infused with a working, healthy version of the mutated gene responsible for the child's disease.

    If the gene therapy is successful, the child will enjoy all the benefits of a stem cell transplant without the potential hazard of graft-versus-host disease.

    Importantly, gene therapy is still an experimental treatment and has its own complications. Children for whom there are no suitable donors or who have a high risk of major complications after a transplant may be candidates for gene therapy.

    In 2010, Boston Children's began an international trial of gene therapy to treat SCID-X1. Read the story of a child who was part of the trial. 

    The study is currently open for enrollment. To learn more, visit the trial listing on ClinicalTrials.gov. To find out if your child may be eligible to participate, please contact David Williams, MD (email); Luigi Notarangelo, MD (email); or Sung-Yun Pai, MD (email).  

    Long-term Outlook

    If your child's immune system is restored to good working order, she should be able to enjoy a rich, active adult life, including having a family.

    It is important to note, though, that some forms of SCID can run in families. For example, SCID-X1 is passed on to boys from mothers who carry the gene mutation on the X chromosome. Genetic counseling is essential for prospective parents with a family history of SCID or any other immune deficiency.

    Helpful links

    Please note that neither Boston Children's Hospital, the Division of Allergy and Immunology at Boston Children's nor the Dana-Farber/Boston Children's Cancer and Blood Disorders Center’s Stem Cell Transplantation Program unreservedly endorses all of the information found at the sites listed below. These links are provided as a resource.

  • At Boston Children's Hospital, our care is informed by our research, and our discoveries in the laboratory strengthen the care we provide at each child's bedside. Boston Children’s scientific research program is one of the largest and most active of any pediatric hospital in the world.

    Boston Children’s has an ongoing gene therapy trial for the X-linked form of SCID (known as SCID-X1). The worldwide, multicenter study is sponsored in the United States by David Williams, MD, chief of Hematology/Oncology and director of Translational Research at Boston Children's.

    The study is currently open for enrollment. To learn more, visit the trial listing on ClinicalTrials.gov. To find out if your child may be eligible to participate, please contact David Williams, MD (email); Luigi Notarangelo, MD (email); or Sung-Yun Pai, MD (email). 

    Touching lives from Argentina to Boston

    Can you imagine how you’d feel if you couldn’t hold your child? Agustin Caceres’s parents could not come in physical contact with him as a baby because he had X-linked severe combined immunodeficiency (SCID-X1), better known as “bubble boy disease.” Read how Boston Children’s and the Dana Farber’s Cell Manipulation Core Facility were able to use gene therapy so he could be in touch with his family and the world again, literally and figuratively. Read more about how Agustin was treated through an international gene therapy trial.

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