More than 15 years ago, 17 babies were born after an experimental infertility treatment that gave them DNA from three people: Mom, Dad, and an egg donor. In this treatment, the mother’s eggs had deficient mitochondria, and a bit of mitochondria-containing cytoplasm from an egg donor was injected into the mother's eggs.
Now researchers have checked up on how the babies are doing as teenagers. The preliminary verdict: The children are all right.
Mitochondria are tiny structures inside nearly every cell of the body that convert food into usable energy. Genes in the mitochondrial DNA don't affect traits like eye and hair color but are important for keeping cells healthy throughout the body.
Some women carry genetic defects in mitochondria and they can pass these on to their children. A recently developed procedure produced a healthy baby by replacing a mother's defective mitochondria with egg donor’s mitochondria. In this case, the procedure was done because the eggs of the mother contained faulty mitochondria causing four miscarriages and the death of two of her children.
The use of donor mitochondria is currently not approved in the United States. The UK has already passed laws to allow the creation of babies from three people, but the mitochondrial transfer will only be allowed when there is a "significant risk" of disability or serious illness in the offspring.
In the mitochondrial transfer procedure, the DNA from the nucleus of the mother's egg is removed and is inserted into an egg from the donor. The nucleus of the donor egg is discarded, but the egg still contained a bit of DNA from the donor. The egg is then fertilized with sperm from the father in in-vitro fertilization.
The likelihood that an egg and a resulting embryo will develop normally depends almost exclusively on preexisting maternal factors especially mitochondria that have accumulated during egg growth and maturation. These egg components are more likely to be lacking or be dysfunctional as a woman ages. Furthermore, a direct correlation exists between the number of mitochondria within the egg and its likelihood of fertilization and preimplantation development.
Being able to replace mitochondria in eggs of women unable to conceive due to their low egg quality may allow, at least some of them, to have babies with only 0.1% of their DNA from the donor (mitochondrial DNA) and all the genetic code for things like hair and eye color from the mother and father.
The fact that children conceived from embryos containing donor mitochondria are doing uniformly well suggests that this procedure could be useful not only for women with genetic mitochondrial defects but also for couples unable to conceive due to suboptimal egg quality.