Adenosine Deaminase Deficiency

The enzyme adenosine deaminase (ADA) works in your cells to remove a toxic product formed in the breakdown of DNA. A child born without the gene for this critical enzyme cannot protect herself from common infections because of resulting damage to her immune system. Although present treatments can improve her immune function, no true cure is presently available.

Adenosine Deaminase Deficiency

Most people have two normal copies of the ADA gene, which codes for this enzyme, although only a single working copy is necessary for good health. ADA deficiency occurs when a baby receives a defective copy of the gene from each of his apparently healthy parents, a condition diagnosed only 10 to 20 times a year in the entire U.S., according to the University of Utah. The enzyme ADA plays an important role in your cells by inactivating a toxic molecule that forms during the routine breakdown of cellular DNA. In ADA deficiency, the lack of this enzyme leads to buildup of the toxic material, which causes cell death, particularly affecting lymphocytes of the immune system.

ADA Deficiency and SCID

Lymphocytes make up a critical part of your immune system, being responsible for producing antibodies that directly attack foreign invaders such as bacteria, viruses and fungi. They are also especially sensitive to the buildup of the toxic molecules in ADA deficiency, resulting in lymphocyte death and a condition referred to as severe combined immunodeficiency (SCID). ADA deficiency patients with SCID are highly susceptible to recurrent life-threatening infections, even from organisms that don't usually cause illness in people with healthy immune systems. Recognition of ADA deficiency typically occurs in the first few months of life, although occasionally milder cases are not diagnosed until later in infancy or, rarely, in adults.

Recognizing ADA Deficiency

Infants with ADA deficiency develop frequent early infections, often caused by unusual organisms. Yeast infections, persistent viral diseases, pneumonia, diarrhea and skin infections commonly occur, as well as multiple ear infections, infections that last two months or more despite antibiotic treatment and deep tissue abscesses. In addition to these immune system problems, ADA-deficient infants can show poor growth and weight gain, developmental delays, hearing loss and movement disorders. Once suspected, a specific diagnosis can be made by testing for the presence of the ADA enzyme in the baby's blood and cells.

Available Treatment Options

Administering antibiotics and intravenous immunoglobulin, and keeping ADA-deficient patients in protective isolation, can help treat or avoid some infections, but not the underlying enzyme deficiency. Bone marrow transplantation, especially from a matching sibling, is the most effective treatment, according to the National Human Genome Research Institute. ADA enzyme replacement with weekly injections can help support the immune system if marrow transplantation can't be performed. Gene therapy, when a normal gene for the ADA enzyme is inserted into a patient's own lymphocytes, has also been partially successful in treating ADA deficiency, although the few children who have had this procedure still receive regular ADA injections to help support their immune systems.

Adenosine Deaminase Deficiency