Severe Combined Immunodeficiency (SCID)

If your child has been diagnosed with SCID, you’ll want to learn as much as you can about this rare condition and the best avenues of treatment for your child. The detailed information on the following pages will help you gain a better understanding of SCID and a clearer picture of what to expect in the days, weeks and months ahead.

Picture the human immune system as an army that constantly patrols, protects and defends the body from all types of “enemies,” including:

• bacteria
• viruses
• parasites

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).

When a child has Severe Combined Immunodeficiency (SCID):

• his body doesn’t produce T cells
• because there are no T cells, the B cells don’t work
• his immune system is virtually nonexistent

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

• pneumonia
• meningitis
• chronic diarrhea
• ear infections
• thrush infections of the mouth and skin
• many other types of infection

Although SCID is often a life-threatening condition, there is cause for hope: new avenues in treatment are helping children with the disorder live longer, more fulfilling lives than ever before. In some cases, prompt intervention can effectively cure SCID altogether.

While the specific course of treatment depend on a child’s individual symptoms and circumstances, many kids with SCID need a 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?
Since SCID is actually a group of different diseases, the exact cause depends on the exact type of disease. However, all types of SCID are genetic – meaning they are caused by an error or mutation in the child’s genes.

The most prevalent type of SCID, known as SCID-X1 (for “X-linked severe combined immunodeficiency”), involves a defect in a gene on the X chromosome. Only male children develop SCID-X1 (girls can pass the disorder on to their sons later in life, but their own immune systems are usually not affected).

Signs and symptoms

What are the symptoms of SCID?
SCID can be difficult to detect because babies with the disorder don’t tend to look or act sick until they develop a telltale infection. In most cases, the infections  are the first indication that a child may have SCID. This is why newborn screening is so important.

FAQ 

Q: How rare is SCID?
A: Very: according the National Human Genome Research Institute, only 40 to 100 babies in the United States are diagnosed with SCID each year.

Q: Is SCID always present at birth?
A: Yes. Even though a newborn may not show any signs of illness right away, since SCID is a genetic disorder (caused by an error in the genes), it is always present at birth.

Q: Is there any test that can detect SCID before symptoms emerge?
A: Yes: newborn screening. In fact, Massachusetts is one of several states that tests for SCID as part of the mandated newborn screening process. Having a screening done is especially important because many infants with SCID show no signs until they actually develop an infection. Learn more about newborn screening with this Children’s Hospital Boston brochure.

Q: Is the rest of my family at risk for SCID? Should my child’s siblings be screened?
A: Having one child with SCID does not necessarily mean other family members, including siblings, are going to develop the disease. However, because SCID is a genetic disorder, it is a good idea to ask your doctor about genetic counseling for yourself and your other children. Learn how the Genetics Program at Children’s can help.

Q: Are there different types of SCID?
A: Yes: medical experts know of at least 10 different types of SCID. The most common is X-linked severe combined immunodeficiency, or SCID-X1, which is caused by a mutation 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, females can be “carriers” that pass the disorder on to their sons later in life).

Your treating clinician can give you specifics about the form of SCID your child has.

Q: Will my child be OK?
A: While SCID is a very serious disorder, the good news is that advances in treatment have made the future much brighter for children and families facing this illness.

Early detection is key: The earlier in a baby’s life SCID is detected, the better the outlook for successful treatment. In some cases, prompt intervention can effectively cure SCID altogether. Though children who are diagnosed later (usually, any time after 6 months old) tend to face a more difficult process and repeated tests and procedures, state-of-the-art treatments like stem cell transplants and gene therapy can make a real difference.

Because children with SCID are at constant risk of infections – including very serious infections – the condition can be life-threatening. However, early diagnosis and proper treatment can help kids with the disorder lead active, fulfilling and healthy lives … something that wasn’t possible just 30 years ago.

Your child’s treatment team will give you all the information you need about his individual symptoms, recommended treatment plan and long-term outlook.

Q: If my child has SCID, does this mean she can’t be around other children, go outdoors or otherwise do anything in a non-sterile environment? Does she need to live in a “bubble”?
A: Any child with SCID has a severely compromised immune system and is at serious risk of developing infections. This means consistent and thorough infection control measures are a must.

However, in many instances, taking simple precautions like having your child wear a mask can be enough to keep her protected before or in between more involved treatments, like a stem cell transplant. Unlike the boy in the 1976 movie, kids with SCID aren’t likely to need a protective “bubble” to keep them safe.

Q: How do I reduce my child’s risk of getting an infection?
A: Your child's physician can give you specific recommendations for lowering his risk of infection. In general, children with compromised immune systems may need to take one or more of the following steps:

• following a strict handwashing regimen, and ensure that your child only comes into contact with others who have washed their hands
• using an air filtration system wearing a mask when leaving the home
• if necessary, taking antibiotics, antifungal or antiviral medications as a preventive measure
• avoiding being in crowds, dirty places or in the company of anyone who is ill or seems to be "coming down with something"

Q: Is it safe for my baby to get the standard childhood vaccinations?
A: As a rule, no. Because the B-cells of children with SCID do not function properly, their bodies cannot produce the normal antibiodies 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.

Q: Why does a stem cell transplant/bone marrow transplant work well for many children with SCID?
A: Stem cell transplants, or bone marrow transplants, work because they essentially re-create a healthy immune system. Stem cells are special cells that can mature into many different kinds of specialized cells. In a stem cell transplant, stem cells from a donor's bone marrow are introduced into the child's system. Once transplanted, they can become white blood cells that rebuild and replenish the child's immune system.

Not every child with SCID will benefit from a stem cell transplant, but the odds of success are very good when:

• the bone marrow comes from a sibling (the optimal scenario) or, if this is not possible, from a parent or other family member
• the transplant takes place within the child's first few months of life

Q: If my child has a stem cell transplant, does this mean he’s cured?
A: If the transplant works - meaning the stem cells develop into normal, functional white blood cells that create a new, working immune system for your child - he may be considered cured. Many kids who undergo a stem cell transplant go on to experience a full return of healthy immune function over time. The younger the child is when the transplant occurs, the better the odds of being completely cured.

Q: Can my child go on to live a normal adult life, including having a family?
A: Yes; 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.

Questions to ask your doctor

You and your family play an essential role in your child’s treatment for SCID. It’s important that you share your observations and ideas with your child’s treating physician, and that you have all the information you need to fully understand the treatment team’s explanations and recommendations.

You’ve probably thought of many questions to ask about your child’s symptoms and prognosis. It’s often very helpful to jot down your thoughts and questions ahead of time and bring them with you, along with a notebook, to your child’s appointment. That way, you will have all of your questions in front of you when you meet with your child’s treating clinician and can make notes to take home with you. (If your child is old enough, you can encourage him or her to write down questions, too.)
 
Initial questions to ask your doctor might include: 

• How did you arrive at this diagnosis?
• Are there any other conditions my child might have instead?
• Does my child require further testing or procedures?
• How extensive is the damage to his immune system?
• Should my other family members be screened for SCID?
• What medications will you prescribe and what are the possible side effects?
• How can I reduce the likelihood of my child contracting an infection?
• Will my child need a stem cell transplant/bone marrow transplant? If yes, how soon and what are the possible risks involved?
• How should I talk to my child about his disease?
• How should I explain my child’s condition to others?
• What other resources can you point me to for more information?