The answer made Ethan Weiss, a physician–scientist at the University of California, San Francisco, think. Weiss is well aware of the rapid developments in gene-editing technologies — techniques that could, theoretically, prevent children from being born with deadly disorders or with disabilities such as Ruthie’s. And he believes that if he had had the option to edit blindness out of Ruthie’s genes before she was born, he and his wife would have jumped at the chance. But now he thinks that would have been a mistake: doing so might have erased some of the things that make Ruthie special — her determination, for instance. Last season, when Ruthie had been the worst player on her basketball team, she had decided on her own to improve, and unbeknownst to her parents had been practising at every opportunity. Changing her disability, he suspects, “would have made us and her different in a way that we would have regretted”, he says. “That’s scary.”
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But emerging technologies are already testing the margins of what people deem acceptable. Parents today have unprecedented control over what they pass on to their children: they can use prenatal genetic screening to check for conditions such as Down’s syndrome, and choose whether or not to carry a fetus to term. Preimplantation genetic diagnosis allows couples undergoing in vitrofertilization to select embryos that do not have certain disease-causing mutations. Even altering the heritable genome — as might be done if CRISPR were used to edit embryos — is acceptable to some. Mitochondrial replacement therapy, which replaces a very small number of genes that a mother passes on with those from a donor, was approved last year in the United Kingdom for people who are at risk of certain genetic disorders.
