What Is Adenosine Deaminase Deficiency?

Adenosine deaminase deficiency is a rare but often lethal disorder that causes damage to the immune system. Children who are born with this deficiency have little or no protection against harmful pathogens. Many babies only survive for one or two years. There was no cure for the disorder in 2011, but certain treatments like blood transfusions and gene therapy help prolong life by improving the immune system.

This disease is autosomal recessive, which means both parents carry a mutated gene that causes adenosine deaminase deficiency. Since each parent only has one gene, they usually do not show symptoms of this abnormality. This form of severe combined immunodeficiency (SCID) occurs when both parents pass the defective gene to their child. This disorder, which is very rare, affected one out of every 200,000 to 1,000,000 children around the world in 2011.

Most people produce an enzyme called adenosine deaminase. This enzyme breaks down deoxyadenosine, which is a dangerous substance that attacks the B and T lymphocytes, and converts them into a harmless molecule called deoxynosine. The B and T lymphocytes help the body fight infection. Children who are deficient in this enzyme do not have enough lymphocytes to fight off harmful pathogens. As a result, they are highly susceptible to bacterial, fungal and viral diseases.

Children who are born with adenosine deaminase deficiency are usually diagnosed in the first few months after birth. These children often suffer from chronic infections; some might develop skin rashes, while others have repeated bouts with respiratory diseases or gastrointestinal issues. They are often smaller in stature than healthy children. Some also have learning problems, hearing loss and developmental delays. Many of these babies do not survive to their second year.

Some individuals do not develop the disorder until they reach early childhood or even adulthood. These patients usually have milder symptoms, but they often have chronic infections, particularly in the ears or lungs, and suffer from various other health issues. The respiratory system can eventually become permanently damaged.

Doctors can test babies for adenosine deaminase deficiency before the mother gives birth by taking a fetal blood sample or by extracting samples of tissue. Children that test positive for the disorder are treated with red blood cell transfusions from donors who have high levels of adenosine deaminase. Some doctors might perform a bone marrow transplant from a healthy sibling or replace the enzymes through regular injections. Gene therapy, which involves inserting healthy synthetic DNA into the immune cells, can also help treat the symptoms of adenosine deaminase deficiency.