Adenosine deaminase (ADA) deficiency
What is Adenosine deaminase (ADA) deficiency?
ADA deficiency is one form of SCID (severe combined immunodeficiency), a disorder that affects the immune system. ADA deficiency is very rare, but very dangerous, because a malfunctioning immune system leaves the body open to infection from bacteria and viruses.
The disease is caused by a mutation in a gene on chromosome 20. The gene codes for the enzyme adenosine deaminase (ADA). Without this enzyme, the body is unable to break down a toxic substance called deoxyadenosine. The toxin builds up and destroys infection-fighting immune cells called T and B lymphocytes.
How do people get ADA deficiency?
ADA deficiency is an autosomal recessive disorder. Both parents need to pass a copy of the defective gene to their child in order for that child to inherit the deficiency.
What are the symptoms of ADA deficiency?
Because ADA deficiency affects the immune system, people who have the disorder are more susceptible to all kinds of infections, particularly those of the skin, respiratory system, and gastrointestinal tract. They may also be shorter than normal. Sadly, most babies who are born with the disorder die within a few months.
How do doctors diagnose ADA deficiency?
Doctors can identify ADA deficiency during the mother's pregnancy (1) by taking a tiny sample of tissue from the amniotic sac where the baby develops (called chorionic villus sampling), or (2) by looking at enzyme levels in a fetal blood sample taken from the umbilical cord. After the child is born, doctors can test a sample of his or her blood to see if it contains ADA.
How is ADA deficiency treated?
There are no real cures for ADA deficiency, but doctors have tried to restore ADA levels and improve immune system function with a variety of treatments:
- Bone marrow transplantation from a biological match (for example, a sibling) to provide healthy immune cells
- Transfusions of red blood cells (containing high levels of ADA) from a healthy donor
- Enzyme replacement therapy, involving repeated injections of the ADA enzyme
- Gene therapy - to insert synthetic DNA containing a normal ADA gene into immune cells
Interesting facts about ADA Deficiency
ADA deficiency is extremely rare. Only about 10 to 20 children are diagnosed with the disease in the United States each year.
In 1990, doctors William French Anderson, Michael Biase, and Ken Culver performed the first successful gene therapy on Ashanti de Silva, a young girl with ADA deficiency.