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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 are found in immune system cells called lymphocytes. These cells defend the body against foreign invaders, such as viruses or bacteria. Lymphocytes are produced in specialized lymphoid tissues throughout the body, including in a gland located behind the breastbone called the thymus and in the lymph nodes.
The function of the adenosine deaminase enzyme is to get rid of a molecule called deoxyadenosine, which is generated when DNA is broken down. A buildup of deoxyadenosine in cells can lead to early cell death. Adenosine deaminase converts deoxyadenosine to another molecule called deoxyinosine, which is not harmful.
Health Conditions Related to Genetic Changes
Adenosine deaminase deficiency
Many variants (also called mutations) in the ADA gene have been found to cause adenosine deaminase (ADA) deficiency. This condition impairs the immune system and causes health problems that typically begin early in life. Most of the ADA gene variants that cause ADA deficiency change single protein building blocks (amino acids) in the adenosine deaminase enzyme. Other variants cause the enzyme to be unstable or prevent it from being produced at all. These variants reduce the levels of functional adenosine deaminase enzyme in cells and prevent the normal breakdown of deoxyadenosine.
The severity of the condition generally depends on how much functional enzyme is available. Individuals with no enzyme activity have ADA deficiency with severe combined immunodeficiency (ADA-SCID). Those with greatly reduced enzyme activity have a form of the condition known as delayed or late-onset combined immunodeficiency (ADA-CID), and those with somewhat reduced enzyme activity have partial ADA deficiency.
A buildup of deoxyadenosine can lead to the early death of lymphocytes, which are very sensitive to changes in the level of adenosine deaminase. The loss of infection-fighting cells results in the signs and symptoms of ADA deficiency.
More About This Health ConditionOther Names for This Gene
- ADA_HUMAN
- adenosine aminohydrolase
Additional Information & Resources
Tests Listed in the Genetic Testing Registry
Scientific Articles on PubMed
Catalog of Genes and Diseases from OMIM
References
- 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
- Ferrua F, Aiuti A. Twenty-Five Years of Gene Therapy for ADA-SCID: From Bubble Babies to an Approved Drug. Hum Gene Ther. 2017 Nov;28(11):972-981. doi: 10.1089/hum.2017.175. Citation on PubMed
- Hershfield M, Tarrant T. Adenosine Deaminase Deficiency. 2006 Oct 3 [updated 2024 Mar 7]. In: Adam MP, Feldman J, Mirzaa GM, Pagon RA, Wallace SE, Amemiya A, editors. GeneReviews(R) [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2025. Available from http://www.ncbi.nlm.nih.gov/books/NBK1483/ 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
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