ADA deficiency

a genetic disorder affecting about one baby in 25,000 and characterized by a defect in adenosine deaminase (ADA), an enzyme that is involved in purine metabolism. Deficiency of this enzyme results in selective damage to the antibody-producing lymphocytes; this in turn leads to a condition known as SEVERE COMBINED IMMUNE DEFICIENCY (SCID), in which the affected baby has no resistance to infection and must be entirely isolated from birth. Such children have only about a 50% chance of surviving for six months. See also GENE THERAPY .