Severe combined immunodeficiency (SCID)

What is severe combined immunodeficiency (SCID)?

Severe combined immunodeficiency (SCID) is a group of inherited immune system disorders that occur during childhood. In these disorders, parts of the immune system are missing or don’t work well, which makes it much harder for the body to fight off infections. Babies born with SCID have many severe infections that keep coming back even after treatment, making it harder for them to gain weight or grow at a healthy rate. Without treatment, SCID is often fatal. However, if detected early and treated properly, babies with SCID have over a 90% survival rate.

The 2 most common types of SCID

There are two common types of SCID, with each having different effects on the body.

Classical X-linked SCID

Also referred to as “bubble boy” disease, classical X-linked SCID affects a gene on the X chromosome and causes white blood cells to grow abnormally. This means that only males can contract this type of SCID.

ADA deficiency SCID

ADA deficiency SCID can affect both males and females, and causes low levels of an infection-fighting molecule called adenosine deaminase (ADA). Infants diagnosed with this type of SCID may not experience problems until later in childhood, adolescence, or even adulthood.

How does blood or marrow transplant (BMT) work for SCID?

A blood or marrow transplant (BMT), also called a bone marrow transplant or blood stem cell transplant, replaces unhealthy bone marrow with healthy blood-forming cells from a donor. Transplant is the only known cure for SCID.

What type of transplant is used for SCID?

For SCID, doctors use an allogeneic transplant, meaning the donated cells come from someone else. These healthy blood-forming cells can come from:

  • A family member
  • An unrelated donor
  • Umbilical cord blood

What to expect during the transplant process for SCID

Although each child’s journey is unique, bone marrow transplantation for severe combined immunodeficiency typically follows a series of distinct phases. From initial therapy to the infusion of donor cells and ongoing recovery, here’s how the transplant process generally works.

  • Preparation: Your child will begin with chemotherapy (and sometimes radiation) to destroy the unhealthy marrow. This step, called conditioning therapy, makes room for new, healthy blood-forming cells.
  • Transplant: Next, healthy donor cells are delivered through an intravenous (IV) catheter, often referred to as a stem cell infusion. These cells travel to the inside of your child’s bones and begin producing new blood cells.
  • Recovery: Full recovery can take several months to a year. From the start of conditioning to leaving the hospital can take weeks to months. Your child will then spend additional time recovering near the transplant center and at home. During this period, your child’s transplant team carefully monitors them, helping prevent and manage any side effects or complications.

When should my child see a transplant doctor for severe combined immunodeficiency?

If your child is diagnosed with SCID, they should see a transplant doctor right away. Young patients who have a closely matched donor and get a transplant soon after diagnosis may have a better chance for a cure.

Your child’s first appointment with a transplant doctor

Scheduling an appointment with a doctor to discuss your child’s SCID diagnosis is the first step to finding a cure. At the first appointment, the transplant doctor will:

  • Review your child’s medical history
  • Talk with you about your child’s SCID treatment options
  • Discuss the risks and benefits of BMT transplant
  • Recommend the best time for your child to get a transplant and prepare for treatment
  • Start a donor search

The role ethnicity plays in finding a match

Patients that come from ethnically diverse backgrounds will often have a harder time finding a matching bone marrow donor. This is because of genes called human leukocyte antigens (HLAs), which are the codes inside your body doctors use to help find a match. HLAs are inherited, which means it will be easier to find a match using a patient and donor that share the same ancestry.

Unfortunately, not all ethnicities are equally represented on the registry. 

Questions to ask your doctor about SCID and the transplant process

Ask questions so you can best understand the treatment options available for your child’s severe combined immunodeficiency. Questions you may want to ask include:

  • What are my child’s chances of curing SCID with transplant? Without transplant?
  • What are the possible side effects of a bone marrow or blood stem cell transplant? How can they be reduced?
  • How might my child’s quality of life change over time due to SCID, with or without transplant?

By asking these questions, you can better understand your options and plan the next steps in your treatment journey.

Discover SCID support services

Explore the full range of services we provide to help children with severe combined immunodeficiency, including group support, emotional and spiritual support, tips for healthy living after transplant and more.