Heather has two mommies

Some women in the United Kingdom could soon give birth to babies with genes from a father and two mothers, if Parliament approves the idea. The country’s Human Fertilisation and Embryology Authority gave a green light in March to special lab procedures allowing women with genetic defects to bear an apparently healthy child.

Biology lesson: Mitochondria, rod-shaped power generators found inside cells, contain DNA that is separate from other DNA in the cell nucleus. Children inherit this mitochondrial DNA from their mother, but not their father. Around 1 woman in 5,000 is affected by mitochondrial mutations that can be passed along to her children and cause muscle, heart, bowel, and other diseases, sometimes resulting in death.

To avoid passing on damaged mitochondrial DNA, doctors can perform a genetic switch in one of two ways: The first method is to remove the nucleus from the mother’s damaged egg and transplant it into a healthy egg from a female donor. Afterward, the resulting egg can be fertilized and implanted in the mother’s womb. The second method is similar but involves switching the nucleus after the mother’s and donor’s eggs have both been fertilized—resulting in the death of one of the embryos. In both cases, the baby that is born would have 99.9 percent of his or her parents’ genes, plus a tiny amount of mitochondrial DNA from the egg donor.

Several children worldwide have already been born with this sort of third-party genetic arrangement, and some are likely teenagers now. In the United States, the Food and Drug Administration warned researchers to stop creating such pregnancies over a decade ago.

Ethical questions abound: Like other forms of in vitro fertilization, manipulation in a lab carries inherent risks to the life of the embryo. It’s also unclear what the long-term health consequences of the genetic “repair” will be, since the donated DNA can be passed down indefinitely to successive generations. Stuart A. Newman, a cell biologist at New York Medical College, called the procedure part of a dangerous “new drive toward DNA-based eugenics.”

Small army

Doctors at the Memorial Sloan-Kettering Cancer Center in New York City have apparently cured three patients of a serious form of leukemia using a promising gene therapy technique. The doctors extracted immune cells from patients with acute lymphoblastic leukemia—a rare blood cancer with a 60 percent fatality rate—and genetically reprogrammed them to fight the disease.

One 58-year-old patient’s leukemia went into remission in just a few weeks using the procedure. The doctors, who described the treatment in Science Translational Medicine, are watching to ensure he does not relapse. The technique of engineering a person’s own cells to battle disease carries potential for other cancers as well. —D.J.D.

Throw ’em back

As federal regulators consider whether to allow sales of the fast-growing “AquAdvantage Salmon,” the first genetically modified animal intended for the U.S. food market, some grocery stores are posting “Keep out” signs. Whole Foods Market, Trader Joe’s, Aldi, and some regional grocery chains have pledged not to sell genetically engineered seafood.

A large proportion of plant ingredients in U.S. foods already come from genetically modified crops, such as corn and soybeans. Regulators say the products are safe, but some consumers have begun avoiding them, worried about unproven health effects. —D.J.D.