“This one-time kind of cure is very much needed,” said Matthews.

The FDA’s approval is the first for Bluebird’s treatment; Vertex has been previously authorized in Britain and Bahrain.

Studies testing the therapies suggest they work well. Of 31 people treated in the pivotal Vertex study with sufficient follow-up, 29 were free of pain crises for at least a year. In the Bluebird study, 28 of 32 patients had no severe pain or organ damage between six and 18 months after the therapy.

But doctors point out there are possible side effects and the long-term outcomes are unknown. For both, the necessary chemotherapy comes with risks such as infertility, hair loss and vulnerability to serious infection.

With the Bluebird therapy, blood cancer has occurred, so the FDA said the label will include a “black box warning” about that risk. With the Vertex therapy, some scientists worry that CRISPR brings the possibility of “off-target effects,” which are unexpected changes to a person’s genome.

“It’s important to be cautious and to be optimistic about this therapy, but also know that there’s still not a ton of experience with it,” said Dr. Benjamin Watkins, director of the pediatric stem cell and cell therapy program at Children’s Hospital New Orleans.

Doctors said they don’t expect every medical center to offer the gene therapies because they require so much equipment and coordination between medical specialists. They also don’t expect lots of people to seek them right away. Watkins said some may want to wait until more people get the treatments.

But eventually, gene therapy “could be transformative and really change the landscape of sickle cell disease,” said Dr. Monica Bhatia, who treats children with the disease at New York-Presbyterian.

Matthews, who volunteers with the Sickle Cell Association of Kentuckiana, said she’s hopeful the treatments will have a big impact.

“It’s a blessing,” she said. “It will really benefit all of us in the sickle cell community.”

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