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Britain is the first country to permit doctors to use genetic material from three people to create human embryos. The process is called mitochondrial replacement therapy, or MRT. Some call it making “three-person babies.” The treatment is meant to help women avoid passing certain diseases and disorders to their children. After the British parliament approved the measure, public reaction and debate was immediate. The therapy could potentially end several severe, sometimes deadly, health problems. But the process behind that goal frightens many and offends others. Here is the science of MRT. A human is made from the genetic information provided by a mother and a father. Almost all our DNA is in the nucleus of our cells. That DNA is called nuclear DNA and makes up about 99.99 percent of our genes. But about one-tenth of one percent of our DNA comes only from our mothers and it is found in organelles called mitochondria. That DNA is called mitochondrial DNA. Mitochondrial DNA does not decide the color of your hair or the texture of your skin, or other features. Instead, the mitochondria are like the cell’s power factory, turning food into energy. A small percentage of women have mitochondrial mutations, which could cause severe diseases in an even smaller number of children. MRT would use DNA from a mother and father, and the mitochondria from a third person. Critics of MRT say it is the first step onto a dangerous path of human gene engineering. They warn of “designer babies” in the future. Supporters deny that claim.
