By Sara Reardon

When a US fertility clinic revealed last year that it had created a baby boy using a controversial technique that mixes DNA from three people, scientists were quick to raise the alarm. Some objected on ethical grounds, and others questioned the scientific claims made by the clinic’s leader, physician John Zhang.

Now, after months of intense debate and speculation, Zhang’s team has provided more details about the child’s conception, in a paper published on 3 April in Reproductive Biomedicine Online1. But major questions remain about the long-term health of the boy, and whether the experiment will ultimately advance reproductive medicine.

Techniques to create ‘three-parent babies’ seek to offer mothers a way to have a child without passing on metabolic diseases caused by faulty mitochondria, the structures that provide energy to cells. Researchers do this by exchanging the diseased mitochondria of a prospective mother with those of a healthy, unrelated donor: the ’third parent’.

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