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Severe combined immunodeficiencies

(Severe • combined • im-MYOO-noh-di-FISH-uhn-seez)

General Condition Information

Other Names

  • SCID
  • Severe combined immune deficiency
  • Severe combined immunodeficiency
  • Severe combined immunodeficiency and related disorders
  • Severe combined immunodeficiency disease
  • Severe combined immunodeficiency syndrome
  • X-linked severe combined immunodeficiency, JAK3-deficient severe combined immunodeficiency, ZAP70-related severe combined immunodeficiency

Condition Type

Birth Prevalence

  • It is estimated that fewer than 80 babies are born with the most common form of this condition each year in the United States. 
  • Visit GeneReviews to learn more about how often this condition occurs.

Screening Finding

Decreased or absent T cell receptor excision circles (TRECs)

What is Severe combined immunodeficiencies

Severe combined immunodeficiencies (SCID) are a group of genetic conditions where a baby is born with a nonworking or poorly working immune system. 

We need the immune system to fight infections. The immune system uses white blood cells called lymphocytes to fight against germs that invade the body. Lymphocytes include T cells, B cells, and natural killer (NK) cells.

In SCID, these T cells, B cells, or NK cells are absent or do not work correctly. There are several types of SCID. The type of SCID your baby has depends on which part of the immune system is problematic. The most common types of SCID are X-linked SCID and adenosine deaminase (ADA) deficiency.

X-linked SCID occurs mostly in boys and is also called “bubble-boy” disease. That is because a boy with the condition, David Vetter, lived in a plastic enclosure for 12 years before the availability of current treatments. In this condition, a protein needed to make normal T cells and NK cells is absent or nonworking. B cells are present, but they cannot work as well without help from the T cells. This type of SCID is in a category called T-B+NK- SCID, named after the types of lymphocytes affected. 

ADA deficiency occurs when the enzyme adenosine deaminase is not made correctly. This enzyme helps remove toxic substances in cells that can destroy lymphocytes. Without working adenosine deaminase enzymes, these toxic products build up and kill all lymphocytes – T, B, and NK cells. This type of SCID is placed in the category T-B-NK- SCID.

There are also many other rare causes of SCID. In all causes of SCID, a change in the baby’s genes leads to similar problems with their immune system.

The most severe type of SCID is referred to as classic or typical SCID.

Another form of the condition is called leaky SCID. Unlike typical SCID, babies with leaky SCID may have small numbers of T cells, or only have T cells that do not work normally. This condition is also called Omenn syndrome.

If the immune system is absent or weak, your baby’s body has trouble fighting infections. They can get sick from germs that do not infect people with normal working immune systems, leading to the signs and symptoms of the condition. Without treatment and special protection from germs, SCID can lead to life-threatening illness or death. 

Newborn Screening and Follow-Up

Condition Details

Treatment and Management

Treatment options for this condition are listed below. It is important to talk to your health care provider about which treatment(s) are best for your baby.

The goal of treatment is to prevent the health problems caused by this condition. Treatments may include the following:

Children who receive early and ongoing treatment for SCID are less likely to have life-threatening infections and illnesses and have better long-term survival. Children who receive bone marrow, thymus transplants, or gene therapy can lead healthier lives.

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