The purpose Is to determine if it is possible to improve or correct the 
severe combined immunodeficiency in children lacking the enzyme adenosine 
deaminase (ADA) by inserting a correct copy of the defective gene 
into a sample of the child's own bone marrow cells in the laboratory and then 
replacing these cells back into the child's body where they should grow 
normal ly. 
CURRENT STATE OF KNOWLEDGE : 
1. ADA deficiency is one cause of severe combined immunodeficiency (SCID) in 
children, a genetic disease in which the white blood cells do not develop 
properly from the bone marrow cells and cannot function to fight infection. 
The absence of the enzyme ADA is thought to prevent breakdown of 
deoxyadenosine, a toxic by-product of normal cell growth. Although other cells 
of the body also lack this enzyme, they do not appear to be affected by this 
overaccumulation, which kills or disables the white blood cells. 
2. ADA deficiency is a genetic disease because it is inherited. Each of the 
parents of an ADA-deficient child has only one normally functioning copy of the 
ADA gene, which is sufficient to keep their white blood cells from harm, and 
one defective gene, which produces little if any ADA enzyme* The child, 
however, has unfortunately inherited the defective copy of the gene from each 
of the parents and has no correct copy. 
3. Until now, medical teams have tried to treat this disease by isolation of 
the child from potential sources of infection, aggressive treatment of 
infections that do occur, and various sources of enzyme replacement including 
the newest form, PEG-ADA. Most attempts at enzyme replacement are only 
temporary solutions because the enzyme only lasts a short time and needs to be 
continually replaced. In addition, the likelihood of complications from these 
treatments increases as they are repeated. 
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Recombinant DNA Research, Volume 12 
