The United Kingdom’s House of Lords has approved legislation to allow a new type of in vitro fertilization (IVF) that would replace faulty DNA, preventing certain types of genetic diseases. The vote follows the House of Commons approval of the measure on 3 February, making the United Kingdom the first country to explicitly allow the procedure, which would combine DNA from two biological parents and an egg donor.

The technique will be allowed under fairly tight regulation: Researchers who wish to offer the service to couples still must apply for and receive a license from the country’s Human Fertilisation and Embryology Authority.

The technique, called mitochondrial DNA replacement therapy, would allow women who have mutations in the DNA of their mitochondria, the organelles that provide chemical energy for cells, to have genetically related children who don’t carry the mutations. It is controversial, however, because it would modify the DNA of an embryo in a way that could be passed on to future generations.

People who have faulty mitochondria can experience a variety of symptoms, including heart problems, seizures, and blindness. The symptoms are variable, however, and the condition can be difficult to diagnose. Some babies born with defective mitochondria die within months. Other people don’t show any symptoms until much later in life.

Mitochondria are passed on through the egg cell, so the diseases are inherited through the mother. 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. And after that egg has been artificially inseminated with sperm, the resulting embryo carries nuclear DNA from the mother and father and mitochondrial DNA from the egg donor.

The United Kingdom has conducted several scientific and ethical studies on the issue since 2011, all of which concluded that the technique was potentially safe and ethical. But some researchers have argued that not enough is known about potential side effects of the technique.

After several hours of debate, the Lords defeated a proposed amendment to the legislation that would have established a committee to further study the possible risks of the technique. They then quickly approved the proposed regulations.

Opponents of the IVF method expressed their dismay afterward. “Unlike experimental gene therapies where risks are taken on by consenting individuals, these techniques turn children into our biological experiments and forever alter the human germline in unknowable ways. There is no precedent for this,” said Marcy Darnovsky, executive director of the Center for Genetics and Society, which has argued against approval of the technique. “We call on those who have supported moving forward with these techniques to make it clear that other kinds of inheritable genetic changes remain off-limits.”

In the United States, the Food and Drug Administration has asked the Institute of Medicine to study the ethical and scientific issues involved in the technique and issue a consensus report. The expert committee’s next meeting is scheduled for 31 March.