Severe combined immunodeficiency (SCID) is a group of genetic disorders that affect the immune system. Children born with SCID are more likely to experience serious illness and infection because their immune system isn’t working properly.

As a result, children who don’t receive treatment may die within the first year or two of life. With treatment, though, SCID is curable.

SCID was previously referred to as “bubble baby disease” due to a movie in the 1980s that highlighted the disorder. The story focused on David Vetter, a child born with SCID who had to live in a plastic bubble for 12 years to avoid contact with infection while doctors searched for a cure.

Here’s what you need to know about SCID, its risk factors, and available treatments.

Inherited mutations in more than a dozen different genes cause SCID. This means one or both birth parents pass down the disease to their child.

SCID is usually a recessive trait. If you only have one copy of the gene mutation, you likely won’t have SCID. However, you’ll be a carrier for the mutation and can pass it down to your children. Some 80% of children born with SCID have no family history of the disorder.

There are several different types of SCID. Doctors classify each type based on the affected gene. That said, specific gene defects are unknown in around 15% of cases.

X-linked SCID

When a mutated gene on the X chromosome causes SCID, doctors call it X-linked SCID. This type primarily affects genetic males, as they carry only one X chromosome. There’s no other copy of the gene to suppress the recessive trait.

Genetic females, on the other hand, don’t typically display symptoms because they have two X chromosomes. Instead, they may be carriers of X-linked SCID.

Adenosine deaminase (ADA) deficiency SCID

When a mutation in the ADA gene causes SCID, doctors call it ADA SCID. People with ADA SCID don’t have T, B, or natural killer (NK) cells to fight off bacterial, fungal, or viral infections. This type is autosomal recessive, which means that children inherit a mutated gene from each parent.

It may show up soon after birth (early onset) or later on (late or delayed onset).

Omenn syndrome

Also referred to as atypical or leaky SCID, Omenn syndrome is a disorder in which people have notable or even excess T cells circulating the blood. Instead of protecting from illness, the excess T cells act like an autoimmune disease and cause inflammation and other damage to the body.

People with Omenn syndrome may experience:

Other types of SCID

SCID may also be due to changes in the following genes (or others):

  • RAG1
  • RAG2
  • NHEJ1
  • CD247
  • CD3E
  • CD3D
  • AK2
  • I7RA

If your child has SCID, a doctor may refer you to genetic testing to determine which gene is affected.

SCID is very rare. It affects up to 1 in every 100,000 babies born in the United States. It also tends to be more common in people of Apache, Navajo, and Turkish backgrounds.

Again, most people born with SCID don’t have a family history of the disorder.

Babies with SCID may not show symptoms soon after birth because their birth parents’ antibodies still protect them. Symptoms tend to appear when a child is between 3 and 6 months old.

The most notable symptom is frequent or recurrent infections that lead to pneumonia or chronic diarrhea. Yeast infections are also common, along with fungal pneumonia (caused by Pneumocystis jirovecii).

Other symptoms in your child may include:

  • trouble gaining weight
  • slow growth
  • weakness
  • rashes
  • diarrhea

Babies with SCID may get sick easily from germs that don’t typically affect people with functional immune systems. They may not respond to antibiotic treatment and may also deal with repeated illness or infections that don’t go away even with treatment. As a result, the most serious complication of SCID is death from severe infection.

Each year, some 4 million newborns in 45 of the 50 states in the United States undergo screening for SCID at birth. Previous to widespread screening, early detection wasn’t common, and the average age for diagnosis was around 6 months, according to 2014 data.

Screening involves sampling dried blood (from a heel prick) and measuring levels of T cells. Specifically, the test measures for T-cell receptor excision circles (TRECs). A low TREC reading on this test means there are low numbers of white blood cells called lymphocytes circulating in the blood.

A doctor will use additional tests to confirm a positive (low) result. Further testing can determine which types of white blood cells are affected.

You’ll need to keep your child healthy before they receive treatment. This means avoiding people who are sick or situations in which viruses or infections may easily spread. A doctor may also recommend that you avoid breastfeeding.

In some cases, the hospital may move your child to a room with filtered air to keep germs at bay until treatment.

Bone marrow transplant

A bone marrow transplant (which includes the transplant of stem cells) is the most effective treatment for SCID. To be most effective, the procedure should generally be done before your child is 3 months old.

The donor is often a healthy relative, such as a sibling or parent. You can also locate a donor through a national search for potential matches. According to 2014 data, most successful transplants usually involve a related family member.

Gene therapy

Gene therapy is an option for babies who aren’t eligible for a bone marrow transplant and for those who have X-linked or ADA SCID. This treatment is considered experimental and is still in clinical trials.

In the procedure, medical staff take a sample of your baby’s bone marrow and insert a “normal” copy of the gene. They then transplant the adjusted bone marrow and stem cells back into your baby’s body a few days later.

Enzyme replacement therapy

Pegademase bovine (PEG-ADA) treatment is an enzyme replacement therapy for children with ADA-related SCID. PEG-ADA therapy isn’t a cure, but it can reduce infections and increase growth. According to 2016 research, it’s linked with a survival rate of up to 78% over 20 years.

Typically, parents use PEG-ADA therapy to keep their child healthy until they can have a stem cell transplant. This treatment involves regular injections of the drug to help replace the missing ADA enzyme.

Early diagnosis is important with SCID. Before diagnosis, your child may experience serious or recurrent infections. The key is to get treatment before these infections take hold. Without treatment, many babies die before their first birthday.

But with treatment, SCID is curable. Treatment can restore your child’s immune system function, and your child can go on to live a long, healthy life.

With early diagnosis and treatment with a bone marrow transplant, the survival rate for SCID is more than 90%.

How can I help my child with SCID?

It can be overwhelming to learn your child has a rare disorder. There are some things you can do to help your little one while you await diagnosis and treatment.

  • Pay attention to illness: Some babies may not be diagnosed with SCID right away. According to 2014 data, it is important to be on the lookout for infections, particularly eight (or more) ear infections, two (or more) cases of pneumonia, and other infections that don’t go away even with antibiotics.
  • Avoid sick people: If your child has been diagnosed with SCID, avoiding infections and illness is the top priority. This may mean steering clear of friends and family for a while until your child has had treatment.
  • Wash your hands frequently: You also have the potential to pass along infections to your child. Be sure to follow good personal hygiene habits, such as washing your hands and wearing a mask, to lower your risk of transmitting any illness.
  • Follow all doctors’ orders: Your child’s medical team may have other suggestions for you. Take notes and ask questions when you’re unsure of what to do. You’re your child’s best advocate.
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Consider making an appointment to discuss your questions with a pediatrician. Your child’s doctor may refer you to a pediatric immunologist, a doctor who specializes in immune system issues.

How likely is it that my future children will have SCID?

SCID is a rare condition. And in 80% of cases, there’s no family history of the disorder. A doctor may suggest genetic counseling or prenatal testing if you have:

  • a family history of SCID
  • a previous child with SCID
  • other risk factors

Can adults get SCID?

No, adults don’t suddenly develop SCID. It’s a genetically inherited condition that causes symptoms (frequent infections) within a few months after birth. Without diagnosis or treatment, most people with SCID don’t generally live past their first or second birthdays.

Can people with SCID get vaccinated for COVID-19?

According to 2014 data, people with SCID tend to have low antibody levels after infection and after receiving vaccinations. Still, experts do recommend vaccination against COVID-19. According to 2021 research, the vaccine is generally safe for people who are immunocompromised.

Talk with a doctor about when to get vaccinated and whether you need additional doses.

SCID is a genetically inherited disorder, which means it may be passed from parents to children during reproduction. While it’s quite rare, it can be fatal if not diagnosed and treated in the first year of life.

The best treatment for SCID is a bone marrow transplant from a sibling or related donor. Speak with a doctor about genetic testing if you have a history of SCID in your family or if you have other concerns about your child’s health.