Severe Combined Immunodeficiency (SCID)

What is severe combined immunodeficiency?

Severe combined immunodeficiency (SCID) is a rare condition that causes babies to be born with little or no immune system.

SCID is a primary immunodeficiency disorder. Immunodeficiency disorders suppress your immune system and keep it from working properly. Immunodeficiency disorders weaken your body’s natural ability to defend itself.

Babies born with SCID can’t fight off infections, even common illnesses that are usually not severe or dangerous. If it’s not treated, SCID is fatal in most children within a year or two.

Types of SCID

Your immune system is like your body’s built-in security system. Usually, it automatically detects substances that shouldn’t be in your body (like viruses, bacteria, fungi, protozoa or toxins) and sends out white blood cells called lymphocytes to eliminate them. The three types of lymphocytes include:

• T-cells.
• B-cells.
• Natural killer (NK) cells.

Babies with SCID are usually missing T-cells. Because T-cells are critical for B-cells to work, these babies will have problems with the types of infections B-cells are supposed to handle, too. That’s what the “combined” in SCID’s name comes from — missing a combination of these important defense cells.

There are different types of severe combined immunodeficiency, depending on which immune cells your child is missing. All of them are equally serious. Your healthcare provider will tell you which type your child has.

How common is SCID?

SCID is rare. It affects around 1 in every 50,000 babies born in the U.S. each year.

Knowing a condition is rare probably doesn’t matter when your baby is diagnosed with it. That’s especially true for an issue like severe combined immunodeficiency (SCID). It makes a scary-sounding, abstract fear into something very real and very important in your life.

What are SCID symptoms?

SCID may not cause any symptoms you can notice. If it does, they usually include:

• Your child not gaining weight at a typical healthy rate.
• Chronic diarrhea.
• Frequent, severe infections.

Your baby’s immune response to infections will be dramatically reduced or absent. That means your child will be much more likely than usual to get sick. And when they do, their symptoms will be much more severe than usual.

Babies with SCID have a higher risk for all types of infections, including:

• Bacterial infections.
• Viral infections.
• Fungal infections.
• Parasitic infections.

Any illness can cause severe symptoms, but some types of infections are more common in babies with SCID, including:

• Yeast infections (thrush or diaper rash).
• Chickenpox.
• Cold sores (herpes simplex).
• Ear infections.
• Pneumonia.
• Meningitis.

What causes SCID?

Severe combined immunodeficiency is a genetic disorder. That means genetic mutations cause it. Experts have identified more than a dozen mutated genes that can cause SCID.

The genetic mutations that cause SCID are passed from biological parents to their children. It can be either autosomal recessive or X-linked. A recessive trait means both biological parents must have the mutated gene that causes a condition. X-linked cases of SCID happen when a mutation on an X chromosome causes it. X-linked conditions usually affect babies assigned male at birth (AMAB) because they only have one X chromosome, while babies assigned female at birth (AFAB) have two.

What are the complications of SCID?

Not having a strong (or any) immune response to infections is the most important SCID complication. Because your child’s body can’t fight off even mild infections, their risk of severe complications is much higher than most children’s.

Illnesses that would normally not be a cause for concern can cause life-threatening complications in children born with SCID.

SCID is almost always fatal if it’s not diagnosed and treated right after a baby is born.

How do healthcare providers diagnose severe combined immunodeficiency?

Providers diagnose SCID with a blood test. Your provider will take a small blood sample from your baby right after birth (usually from your child’s heel).

All 50 states in the U.S. screen every baby born for SCID. This is important to help identify babies that need treatment right away so they don’t get a severe infection immediately after birth.

Can SCID be treated?

Babies with SCID need a stem cell transplant (bone marrow transplant) as soon as possible. A stem cell transplant will replace your baby’s stem cells with a sample from a donor. The healthy stem cells will replace your child’s immune system and help their body fight infections.

Biological siblings that don’t have SCID are the best stem cell donors. If you don’t have another biological child who can donate stem cells, your healthcare providers will check stem cell registries — databases that allow providers to look for matching stem cells donated by the public.

Your child might need other treatments while they’re waiting for a stem cell transplant, including:

• Antibiotics.
• Antivirals.
• Antifungals.
• IVIG infusions.
• Gene therapy.

These are all temporary treatments that won’t cure the SCID, but can help your child fight infections before their stem cell transplant. Only a stem cell transplant can permanently cure SCID.

Your child might also need to stay in sterile isolation while they’re waiting for a stem cell transplant. This means they’ll stay in a medically sterile environment where everything that enters their room or space will be sterilized to make sure it doesn’t have any germs on it.

People sometimes refer to SCID as “bubble baby disease” because babies with SCID have to stay in sterile isolation to keep them safe. This name isn’t medically accurate, and is potentially hurtful. You and your baby didn’t do anything wrong, and there’s nothing funny about your child’s health condition.

Can I prevent severe combined immunodeficiency?

Because genetic mutations you can’t control cause SCID, there’s nothing you can do to prevent it. Talk to your healthcare provider about genetic counseling if you’re worried about the risk of passing genetic conditions to your biological children.

What can I expect if my child has SCID?

SCID can be fatal if it’s not treated right away. If you live in the U.S., your baby will be screened for it when they’re born. Knowing they have SCID right away is extremely important. The sooner your providers diagnose it and get your child scheduled for a stem cell transplant, the better their chances of survival are.

You might not be able to hold or visit with your baby the way you expected. If they’re in sterile isolation, you’ll have to follow strict health and safety rules to keep them protected from germs and getting sick. Your providers will tell you how you can keep your baby safe, and what you can expect before and after they receive a stem cell transplant.

What is the life expectancy of a baby with SCID?

Babies with untreated SCID usually die within a year or two. Children who’ve had a successful stem cell transplant have a typical life expectancy. Once their body develops a stronger, complete immune system, they usually don’t have long-term complications.

When should I see my healthcare provider?

Visit a healthcare provider if your baby gets sick often, or if they’re experiencing severe symptoms of an illness.

If you know your child has SCID, call your provider right away if you notice any changes in your child’s health. Getting them antibiotics or other medications as soon as possible is an emergency because their body can’t fight infections on its own.

Which questions should I ask my healthcare provider?

You may want to ask your provider:

• Does my child have SCID or another type of immunodeficiency?
• Will my baby need to stay in sterile isolation?
• When will my child need a stem cell transplant?
• Which changes or symptoms in my child should I watch out for?

A note from Cleveland Clinic

It might feel like all the air is sucked out of the room when you find out your child has SCID. But don’t be afraid to ask your providers any questions you have. It’s critical that your child get scheduled for a stem cell transplant as soon as possible, but you deserve to understand everything that’s going on. Your providers will explain everything and let you know what to expect.