Designer babies or an end to intractable illnesses: A revolutionary technology is letting scientists learn to rewrite the genetic code, aiming to alter DNA in ways that could erase disease-causing genes.
Hundreds of scientists and ethicists from around the world gather in Washington this week to debate the boundaries of human genome editing, where researchers spot a gene defect inside living cells and swap it out.
It's all experimental so far, but the promise for new treatments is huge. The ethical quandary: Should it also be attempted in human embryos - altering a gene in not just one person but his or her descendants?
"This is really a decision that will affect us all," said Marcy Darnovsky of the Center for Genetics and Society advocacy group, who opposes heritable gene editing. She called it potentially a "society-altering technology."
But pioneer Jennifer Doudna of the University of California, Berkeley, warns that a ban on even basic gene editing research in embryos could block discoveries. Writing in the journal Nature, she urged scientists to find "an appropriate middle ground."
While scientists have long been able to find defective genes, fixing them has been so cumbersome that it's slowed development of genetic therapies. With gene editing, scientists home in on a piece of DNA and use molecular tools that act as scissors to snip that spot - deleting a defective gene, repairing it or replacing it.
There are some older methods but a new tool called CRISPR-Cas9 has been adopted by laboratories worldwide because it's faster, cheaper, and simple enough to use with minimal training.
Much like a bone marrow transplant, researchers hope to use CRISPR for diseases like sickle cell, correcting the faulty gene in someone's own blood-producing cells rather than implanting donated ones.
Meanwhile, altering genes in sperm, eggs or embryos can spread those changes to future generations, so-called germline engineering that might one day stop parents from passing inherited diseases to their children.
Chinese scientists reported the first-known attempt to edit human embryos last spring, working with leftovers from fertility clinics that never could have developed into fetuses. They aimed to correct a deadly inherited gene, but uncovered problems that require more research.
Germline engineering "has been viewed almost universally as a line that should not be crossed," National Institutes of Health Director Francis Collins said at the time.
Future generations couldn't consent, and any long-term negative effects might not become apparent for years. There's also concern about babies designed for better intellect or appearance rather than to prevent disease.
