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The Second Coming of Gene Therapy

Posted on: 3 September 2009, source: Discover magazine
For years, gene therapy produced tons of hype but no results. Recently, though, new approaches have yielded its first successes: breakthrough treatments for blindness, cancer, and the deadly bubble boy disease.
“For the first two years of her life, my daughter, Katlyn, was knocking on heaven’s door every day,” says Daisy Demerchant, a 26-year-old mom living in Centreville, New Brunswick, just north of Maine. “Two months after she was born she started getting sick, and she never got better.” At six months Katlyn was diagnosed with “bubble boy” disease, formally known as severe combined immunodeficiency (SCID), which robs the immune system of the ability to fight infection. There are many causes of this disorder; in Katlyn’s case it was lack of the enzyme adeno­sine deaminase, or ADA, which rids the body of a natural toxin called deoxyadenosine. When the toxin builds up, it destroys T and B lymphocytes, the body’s infection-fighting immune cells. As a result, Katlyn’s immune cells were dying.

Treatment options ranged from risky to grim. One was a bone marrow transplant, in which imported donor cells could manufacture healthy T cells to fight invading germs. But bone marrow transplants can have lethal complications and often require drugs that further inhibit the patient’s immune system, leaving a window of vulnerability until the transplant kicks in. Another potential treatment involved injections of the ADA enzyme itself. But there was a risk Katlyn would develop antibodies to the drug, rendering it useless. Without any treatment at all, she would simply die.

While weighing their options, doctors put the little girl on protective antimicrobials and sent her to a hospital eight hours from her home. She became another fragile bubble baby sequestered from the world. “My husband quit his job building fire trucks, and we lived with Katlyn in the hospital for 15 months,” Demerchant says. The parents had to wear sterile gowns, booties, masks, and gloves, and the urge to touch their child—let alone hug and kiss her—had to be put on hold.

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