Adenosine Deaminase Deficiency

Gene : ADA

What is Adenosine Deaminase Deficiency?

Adenosine deaminase (ADA) deficiency is an inherited disorder characterized by repeated, persistent, and potentially life-threatening infections. Symptoms are due to a defect in the production of an enzyme called adenosine deaminase. Without normal levels of this enzyme, toxic chemicals build up within the immune system leading to severe immunodeficiency, and the body's ability to fight infectious disease is absent or severely compromised. The severe form of ADA deficiency is also known as ADA-deficient severe combined immunodeficiency (SCID). Children with SCID lack virtually all immune protection from bacteria, viruses, and fungi. Affected children can have growth and developmental delay. Most individuals with ADA deficiency are diagnosed with SCID in the first 6 months of life. Without treatment, these babies usually do not survive past age 2 because of life-threatening infection. In about 10 percent to 15 percent of cases, onset of immune deficiency is between 6 and 24 months of age (delayed onset) or even until adulthood (late onset). Once diagnosed, most patients affected by SCID can be cured by bone marrow transplantation from a donor, though there are risks with the procedure. Other methods, including enzyme replacement for the defected adenosine deaminase, and gene therapy, are in clinical trials. Adenosine deaminase deficiency is caused by pathogenic variants in ADA gene.

How is Adenosine Deaminase Deficiency inherited?

Adenosine deaminase deficiency is inherited in an autosomal recessive manner. This type of inheritance requires the presence of two copies of a pathogenic variant in the gene for a person to have the genetic disease. Both parents must be carriers of a pathogenic variant in the gene in order to be at risk to have an affected child. The child must inherit a pathogenic variant from each carrier parent in order to be affected. There is a 1 in 4 chance that a baby will inherit two mutated copies of the gene and be affected when both parents are carriers.

What does it mean to be a carrier?

There are generally no signs or symptoms associated with being a carrier for adenosine deaminase deficiency. However, the risk to have a child affected with these disorders is increased. Testing of reproductive partners is recommended for carriers of adenosine deaminase deficiency.

How common is Adenosine Deaminase Deficiency in general population?

Adenosine deaminase deficiency occurs in 1 in 200,000 newborns. It accounts for about one-third of all cases of autosomal recessive severe combined immunodeficiency (SCID) and approximately 15 percent of all cases of SCID.

Family References and Resources
Clinician References
What is Analyzed?
  • Full gene sequencing
Affected Systems



Carrier Rates
Detection Rate
Carrier Frequency
General Population > 90% 1 in 224

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