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A mitochondrion.

A mitochondrion.

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U.K. Parliament approves controversial three-parent mitochondrial gene therapy

The United Kingdom’s House of Commons voted overwhelmingly today to allow British researchers to pursue a new fertility treatment that could prevent certain kinds of genetic diseases. The technique, called mitochondrial DNA replacement therapy, could allow women who carry disease-causing mutations in their mitochondrial genes to give birth to genetically related children free of mitochondrial disease.

The measure, which passed 382 to 128, has been controversial, especially because it would alter the DNA of an embryo in a way that could be passed on to future generations. Some scientists and nongovernmental organizations have argued that not enough is known about possible side effects of the technique to go forward in human patients. “We believe the House of Commons has made a serious mistake, which we hope does not have dire consequences,” said Marcy Darnovsky, executive director of the Center for Genetics and Society in Berkeley, California, in a statement.

Proponents of the measure quickly began to celebrate. “I am delighted that [members of Parliament] have voted to allow the introduction of mitochondrial transfer techniques into the clinic," said John Tooke, president of the Academy of Medical Sciences in London, in a statement. Robert Meadowcroft, head of the Muscular Dystrophy Campaign in London, added: “We have finally reached a milestone in giving women an invaluable choice, the choice to become a mother without fear of passing on a lifetime under the shadow of mitochondrial disease to their child."

Mitochondria are the energy-producing engines of a cell. These organelles contain their own set of genes, called mtDNA. When mitochondria don’t work properly, a variety of symptoms can result, which can make mitochondrial diseases difficult to recognize and diagnose. Some babies born with defective mitochondria die within months. Other people don’t show any symptoms until much later in life.

Researchers have developed ways to transfer the genetic material from an egg cell that carries faulty mitochondria into a donor egg that has healthy mitochondria. The resulting embryo carries nuclear DNA from the mother and father and mitochondrial DNA from the egg donor.

Some scientists have argued that potential mismatches between donated mtDNA and host nuclear DNA could cause unanticipated problems. However, several ethical and scientific reviews and a public consultation in the United Kingdom all supported allowing the Human Fertilisation and Embryology Authority (HFEA) to grant licenses for experimental use of the technique in humans. (Previously, HFEA was not allowed to grant licenses for any techniques that would alter the DNA in an embryo.)

The measure must also be passed by the House of Lords. Approval does not necessarily mean that the technique will be used. Fertility clinics will have to apply for a license to use the technique, and each application will be judged on its own merits.

Regulators in the United States are also considering whether to allow the technique. The Food and Drug Administration held a 2-day hearing on the science of mtDNA replacement last year. They have asked the Institute of Medicine to issue a consensus study on the ethical and social policy issues the technique raises. The committee held its first meeting on 27 January; further meetings are planned for March and May.