What Is ADA Deficiency?

Adenosine deaminase (ADA) deficiency is an inherited disorder that affects the immune system. This disorder is considered a type of severe combined immunodeficiency (SCID). Extremely rare and often fatal, ADA deficiency seriously compromises the immune system's ability to fight off bacterial and viral infections. Though ADA deficiency is an incurable disease, treatments have been developed that manage the disorder to some degree.

Inheritance

• ADA deficiency is a type of inherited genetic disorder called an autosomal recessive disorder. This means a child must inherit the defective gene from both parents to develop the deficiency. The inherited gene mutation interferes with the production of the adenosine deaminase enzyme. Deficiency of this enzyme leads to a buildup of deoxyadenosine, a toxin that destroys the T and B lymphocyte cells of the immune system.

Symptoms

• Since ADA deficiency affects the immune system's ability to fight off pathogens, the most common symptom of the disorder is a general susceptibility to infection, though sufferers are particularly vulnerable to skin, respiratory and gastrointestinal infections. People with ADA deficiency are also often found to be of below-average height.

Diagnosis

• ADA deficiency may be diagnosed prior to a child's birth through chorionic villus sampling, which involves taking a sample of tissue from the amniotic sac, or a blood sample from the fetal umbilical cord and checking its enzyme levels. After the child is born, she can be tested for ADA deficiency through a blood test that checks levels of ADA in the blood.

Treatment

• Treatment for ADA consists of restoring ADA levels and improving overall immune system function. ADA levels can be raised through transfusions of blood that's high in ADA, as well as through enzyme replacement therapy, which consists of regular injections of the enzyme. Gene therapy can be used to replace the abnormal gene causing the disorder with a normal gene; this involves injecting synthetic DNA into immune cells. Bone marrow transplantation can be used to provide healthy immune cells, replacing those destroyed by the disorder.

Frequency

• In the United States, ADA deficiency is only diagnosed in 10 to 20 children per year. Most children born with the disorder survive for only a few months.