The CRISPR technique holds the promise of targeting specific mutations in the DNA strand without affecting normal cells. Studies in the mouse model have run into problems, however. “There always is a risk that the technique is not selective enough to prevent the snipping of ‘normal’ portions of the strand or, potentially worse, inserting cells in the wrong place. Other concerns occur when only some of the embryo cells are repaired, called mosaicism,” Dr. Welling noted. Even in the landmark Nature study, the reported success rate was 72.4%. Most scientists agree that before this technique could be used in viable human embryos, the success rate would have to be 100% in the mouse models and larger animal studies.
Patients with more than one mutation pose another hurdle, Dr. Staecker said. “You would have to design a specific editing therapeutic for each one of those spots, so that makes it very expensive from a manufacturing standpoint, and only a fraction of those dominant type alleles would be treatable that way,” he said.
One of the foundations of medical ethics is benevolence, … but we have to balance that with the potential risks, especially when you are talking about changing the DNA of future generations. —G. Richard Holt, MD