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ADA gene

adenosine deaminase

Normal Function

The ADA gene provides instructions for producing the enzyme adenosine deaminase. This enzyme is produced in all cells, but the highest levels of adenosine deaminase occur in immune system cells called lymphocytes, which develop in lymphoid tissues. These lymphoid tissues include the thymus, which is a gland located behind the breastbone, and lymph nodes, which are found throughout the body. Lymphocytes form the immune system, which defends the body against potentially harmful invaders, such as viruses or bacteria.

The function of the adenosine deaminase enzyme is to eliminate a molecule called deoxyadenosine, which is generated when DNA is broken down. Adenosine deaminase converts deoxyadenosine, which is toxic to lymphocytes, to another molecule called deoxyinosine, which is not harmful.

Health Conditions Related to Genetic Changes

Adenosine deaminase deficiency

More than 70 mutations in the ADA gene have been identified. Most of these mutations result in the substitution of one protein building block (amino acid) for another amino acid in the adenosine deaminase enzyme. Other mutations cause the enzyme to be unstable or prevent it from being produced at all.

These mutations result in the absence or deficiency of the adenosine deaminase enzyme in cells, preventing the normal breakdown of deoxyadenosine. A buildup of this toxic compound interferes with the development and maintenance of lymphocytes, resulting in severe combined immunodeficiency (SCID), which is characteristic of adenosine deaminase deficiency.

More About This Health Condition

Other Names for This Gene

  • adenosine aminohydrolase

Additional Information & Resources

Tests Listed in the Genetic Testing Registry

Scientific Articles on PubMed

Catalog of Genes and Diseases from OMIM

Gene and Variant Databases


  • Blackburn MR, Thompson LF. Adenosine deaminase deficiency: unanticipated benefits from the study of a rare immunodeficiency. J Immunol. 2012 Feb 1;188(3):933-5. doi: 10.4049/jimmunol.1103519. No abstract available. Citation on PubMed or Free article on PubMed Central
  • Buckley RH. Molecular defects in human severe combined immunodeficiency and approaches to immune reconstitution. Annu Rev Immunol. 2004;22:625-55. doi: 10.1146/annurev.immunol.22.012703.104614. Citation on PubMed
  • Hershfield MS. Genotype is an important determinant of phenotype in adenosine deaminase deficiency. Curr Opin Immunol. 2003 Oct;15(5):571-7. doi: 10.1016/s0952-7915(03)00104-3. Citation on PubMed
  • Hershfield MS. New insights into adenosine-receptor-mediated immunosuppression and the role of adenosine in causing the immunodeficiency associated with adenosine deaminase deficiency. Eur J Immunol. 2005 Jan;35(1):25-30. doi: 10.1002/eji.200425738. Citation on PubMed
  • Nyhan WL. Disorders of purine and pyrimidine metabolism. Mol Genet Metab. 2005 Sep-Oct;86(1-2):25-33. doi: 10.1016/j.ymgme.2005.07.027. Citation on PubMed

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.