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Knowing the facts about congenital athymia can help you take a more active role now and in the future.

Facts About Congenital Athymia


Pediatric congenital athymia is an ultra-rare immune disorder in which a child is born without a thymus—an organ that plays a critical role in helping the body learn to fight off infections. Congenital athymia affects about 17 to 24 infants out of every 4 million born each year in the United States alone.

T Cell

Children with congenital athymia may have repeated, often life-threatening infections because they don’t have enough working T cells (infection-fighting white blood cells) to fight them off. It’s important to know that these infections can be fatal.

Congenital athymia is different from a similar disorder called severe combined immunodeficiency (SCID). In SCID, there is not a problem with the thymus; SCID is due to a certain problem with bone marrow cells called stem cells.

Learn what to expect when you’re getting to know your medical and support team.

Role of the Thymus

The thymus is an organ that sits on top of the heart, behind the sternum (the long, flat bone located in the central part of your chest). The thymus plays a central role in everyone’s immune system. It is largest and most active in babies and gradually gets smaller as we age.

The immune system is made up of cells and proteins that work throughout the body to fight infections caused by viruses, bacteria, fungi, and parasites.

You can think of the thymus as the “schoolhouse” of the immune system, where important white blood cells called T cells mature and learn to fight infections. T cells are responsible for attacking and remembering foreign invaders. (The “T” is for “thymus.”)

Causes of Congenital Athymia


Congenital athymia usually occurs in babies who have certain genetic problems, especially DiGeorge syndrome (DGS, sometimes referred to as 22q11.2 deletion syndrome).

Some children with DGS have congenital athymia. They may also have other problems, including heart defects, facial abnormalities, low blood calcium, and delayed development with behavioral and emotional problems. However, different people with DGS can have very different symptoms.


Rare genetic conditions known as CHARGE syndrome and FOXN1 deficiency are other possible causes of congenital athymia.

Not everyone with congenital athymia has a related syndrome or genetic condition, and not everyone with a related syndrome or genetic condition has congenital athymia. For some patients with congenital athymia, there may be no identifiable cause.

Daughter looking at father, at a table Daughter looking at father, at a table
Daughter looking at father, at a table

Congenital athymia is first detected by a newborn screening test that is utilized in all 50 US states. Based on the results of this test, the doctor uses a technique called flow cytometry to diagnose congenital athymia. A child is typically diagnosed with this condition within the first few weeks of life.

Once congenital athymia is diagnosed, your doctor will test for other conditions that are often associated with the disorder.

Learn more about strategies for living with congenital athymia.