ADA deficiency is a rare genetic disease. The normal ADA gene
produces an enzyme called adenosine deaminase that is essential
for effective immune system function.
Patients with this condition do not have normal ADA genes, and
their defective genes do not produce the functional ADA enzyme.
ADA-deficient children are born with severe immunodeficiency and
are prone to repeated serious infections, which may be
life-threatening. Although ADA deficiency can be treated with a
drug called PEG-ADA, the drug is expensive (more than $60,000 a
year) and must be taken for life by injection into a vein.
ADA deficiency was selected for the first approved human gene
therapy trial for several reasons:
+ The disease is caused by a defect in a single gene, which increases the likelihood that gene therapy will succeed.
+ The gene is regulated in a simple, "always on" fashion,
unlike many genes whose regulation is complex.
+ The amount of ADA present does not need to be precisely
regulated. Even small amounts of the enzyme are known to be
beneficial, while larger amounts are also tolerated well.
The first clinical trial of gene therapy began in September 1990.
Two children diagnosed with ADA deficiency were treated with this
new approach. As a precaution, they also continued to receive
weekly doses of the drug PEG-ADA. The children's immune status
improved after they received the gene therapy; however, it worked
for only a few months and had to be repeated several times over
the next 2 to 3 years. Since then, the children have had periodic
tests which confirm that their re-engineered cells are surviving
and producing the ADA enzyme. Both now take smaller doses of
PEG-ADA to keep their disease under control.
· 1 decade ago