Severe Combined Immunodeficiency (for Parents)
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Severe Combined Immunodeficiency

What Is Severe Combined Immunodeficiency?

Severe combined immunodeficiency (SCID) is very rare genetic disorder that causes life-threatening problems with the immune system. It is a type of primary immune deficiency.

About 50 to 100 babies are born with in the U.S. each year.

What Happens in Severe Combined Immunodeficiency?

In a developing baby, the immune system starts in the bone marrow. Stem cells there can become any of three different types of blood cells:

  • red blood cells
  • white blood cells
  • platelets

White blood cells protect the body from infections and foreign invaders. There are different kinds of white blood cells, including lymphocytes (lim-FOE-sites). Lymphocytes come in two main types: B-cells and T-cells. These cells are key to fighting infections:

  • T cells identify, attack, and kill "invaders"
  • B cells make antibodies that "remember" an infection and are ready in case the body is exposed to it again

SCID is called "combined" immunodeficiency because it affects both of these infection-fighting white blood cells.

In SCID, the child's body:

  • can't make T cells
  • doesn't have working B cells
  • has an immune system that doesn't work well or, in some cases, at all

Because the immune system doesn't work as it should, it can be difficult or impossible for it to battle the germs — , , and — that cause infections.

What Causes Severe Combined Immunodeficiency?

There different kinds of severe combined immunodeficiency. The most common type is caused by a problem in a gene found on the X and affects only males. Females can be carriers of the condition, but because they also inherit a normal X chromosome, their immune systems can fight infections. Males, though, only have one X chromosome, so if the gene is abnormal the disease appears.

Another form of SCID is caused by a deficiency of an that is needed for lymphocyte development. Other types of SCID are caused by a variety of other genetic problems.

What Are the Signs & Symptoms of Severe Combined Immunodeficiency?

Babies with SCID appear healthy at birth, but problems can start soon after, such as:

If a child has these symptoms, a doctor will test for SCID or other types of immune deficiency.

How Is Severe Combined Immunodeficiency Diagnosed?

All newborns in the United States get screening tests. Doctors use a simple blood test to screen the babies for a number of conditions that could cause health problems, such as sickle cell disease and cystic fibrosis. The conditions screened for vary by state, but all now screen for severe combined immunodeficiency.

Parents who have a child with SCID or a family history of immunodeficiency might want to consider genetic counseling and early blood testing. Early diagnosis can lead to quick treatment and ensure a good outcome. It may also be possible to test a high-risk baby for the disease before birth if the genetic causing SCID in a family is known.

Children without a known family history of the disease are often not diagnosed until 6 months of age or older.

How Is Severe Combined Immunodeficiency Treated?

SCID is a pediatric emergency. The only cure is a stem cell transplant (also called a bone marrow transplant). This means the child receives stem cells from a donor. The hope is that these new cells will rebuild the child's immune system.

The most successful stem cell transplants usually are done with cells donated by a sibling. Sometimes, a parent's stem cells are a match. If no family members are suitable donors, doctors may use stem cells from an unrelated donor.

A baby with SCID who gets a stem cell transplant in the first few months of life is very likely to survive. Infants who get a transplant later are at risk for serious infections.

Gene therapy as a treatment for SCID has shown promising results in clinical trials, but has some risks so is not yet widely used. This involves:

  • removing cells from a child with SCID
  • inserting healthy genes into the cells
  • transplanting the cells back into the child

When the cells reach the bone marrow, they can start to make healthy immune cells. Research on gene therapy for SCID is ongoing.

In cases of SCID caused by a missing enzyme, the enzyme can be replaced via a weekly injection. This is not a cure and these children must get enzyme replacement injections for the rest of their lives.

Children with SCID usually are cared for by a medical team led by a doctor who specializes in treating immune deficiencies, such as a pediatric immunologist or pediatric infectious disease expert.

What Else Should I Know?

Children with SCID:

  • can't get the rotavirus vaccine, which is made with a live rotavirus strain. Because they lack the normal defense of antibodies to the viruses, introducing a virus to a child with SCID, even a weakened vaccine virus, can be dangerous. They also should not get the chickenpox (varicella) vaccine, the measles, mumps, and rubella (MMR) vaccine, or FluMist vaccines. Anyone living in the same household as the baby also should not receive any live vaccines.
  • who need blood transfusions must get blood that has been irradiated (exposed to an X-ray) to kill white blood cells, because live white cells might attack the body
  • may get antibiotics to prevent infection and stay in an isolation room in the hospital
  • might be given an infusion of immuneglobulin (IVIG) to help the body fight infection

How Can I Help My Child?

Until your child's immune system rebuilds after a bone marrow transplant, help reduce the risk of infection by:

  • having your child wear a mask, which also can be a signal to others that your child is trying to avoid infection
  • keeping your baby away anyone with a cold or infection
  • avoiding crowded public places
  • making sure that family members and other caregivers wash their hands well before touching your baby

Looking Ahead

Babies with SCID may need many procedures and repeated hospital stays. That can be stressful for any family. But you're not alone. The care team is there for you and your child before, during, and after treatment. Support groups, social workers, and family friends can also lend a helping hand or understanding ear.

For more information or support online, visit: