Eight healthy babies with DNA from three parents have been born in the United Kingdom as part of an experimental procedure, Sky News reports.

The procedure is available to women at risk of passing on serious conditions, particularly mitochondrial dysfunction. The identities of the babies and their parents have not been disclosed, but one of the mothers said that “hope, joy, and deep gratitude have replaced the burden of disease.”

As CNN explains, the babies carry DNA from three people: the mother’s egg, the father’s sperm, and mitochondria from a donor. Approval for this method required changes to UK legislation in 2016.

In total, 22 women underwent the procedure, but only seven were able to conceive. Eight babies were born, five of whom showed no signs of inherited disorders. The success rate was 36%.

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