Monkeys Born of Two Mothers

Scientists have used techniques similar to cloning to produce monkeys with the genes of two mothers. The research could lead to prevention of some inherited diseases in humans, the researchers say.

In short, the researchers replaced most of the genes in the eggs of one monkey with genes from another. Then the eggs were fertilized with sperm and put back into the womb. Healthy twins were born, nicknamed "Mito" and "Tracker."

"We believe this discovery in nonhuman primates can rapidly be translated into human therapies aimed at preventing inherited disorders passed from mothers to their children through the mitochondrial DNA, such as certain forms of cancer, diabetes, infertility, myopathies and neurodegenerative diseases," said study leader Shoukhrat Mitalipov at the Oregon Health & Science University.

The work is detailed today in the journal Nature.

Mitochondria are structures that are found in all cells that provide energy for cell growth and metabolism, which is why they are often called the cell's "power plant." The structures produce energy to power each individual cell. Mitochondria also carry their own genetic material.

There are 150 known diseases caused by mutations of the mitochondrial DNA, "and approximately 1 out of every 200 children is born with mitochondrial mutations," Mitalipov said in a statement.

"This is of great importance. This approach will be beneficial to many families," Jan Smeitink, a professor of mitochondrial medicine at Radboud University Nijmegen in the Netherlands, is quoted as saying by The Washington Post.

There are ethical concerns, however.

"With this you have potentially three genetic parents," said David Magnus, director of Stanford University's Center for Biomedical Ethics, in the Post. "This will create the potential for legal and social conflicts."

Here's how the new technique works, as explained by the Oregon Health & Science University statement:

When an egg cell is fertilized by a sperm cell during reproduction, the embryo almost exclusively inherits the maternal mitochondria present in the egg. This means that any disease-causing genetic mutations that a mother carries in her mitochondrial DNA can be passed on to her offspring. The method developed by OHSU researchers transfers the mother's chromosomes to a donated egg that has had its chromosomes removed, but which has healthy mitochondria, thereby preventing the disease from being passed on to one's offspring.

Scientists collected groups of unfertilized eggs from two female rhesus macaque monkeys (monkeys A and B). They then removed the chromosomes, which contain the genes found in the cell nucleus, from the eggs of monkey B, and then transplanted the nuclear genes from the eggs of monkey A into the eggs of monkey B. Then the eggs from monkey B, which now contained their own mitochondria but monkey A's nuclear genes, were fertilized. The fertilized eggs developed into embryos that were implanted in surrogate monkeys.

Follow-up testing showed that there was little to no trace of cross-animal mitochondrial transfer using this procedure. This demonstrates that the researchers were successful in isolating nuclear genetic material from mitochondrial genetic material during the transfer process.

"In theory, this research has demonstrated that it is possible to use this therapy in mothers carrying mitochondrial DNA diseases so that we can prevent those diseases from being passed on to their offspring," added Mitalipov. "We believe that with the proper governmental approvals, our work can rapidly be translated into clinical trials for humans, and, eventually, approved therapies."

The research was funded by the Oregon National Primate Research Center, the Oregon Stem Cell Center; and the National Center for Research Resources and the National Institute of Child Health and Human Development, both components of the National Institutes of Health.