Passing on genetic mutations for disease is one of the greatest fears among parents-to-be, but a new technique may alleviate some of those worries.
Mitochondrial disorders affect about 1 in 10,000 people and can cause a range of medical problems from stunted growth, vision loss, neurological disorders to kidney disease. Some of these originate in mutations that code for mitochondria, which are the cell’s workhorses that churn out the energy a cell needs in order to function. Other aberrations can arise from mitochondria’s own DNA; mitochondria hold a unique place in human biology because they contain their own unique DNA and can make their own proteins, apart from the proteins that the cell manufactures.
Currently, there are no cures for mitochondrial disorders, many of which are passed from mother to child since children inherit their mother’s mitochondrial DNA from the egg. Symptoms of these conditions typically appear in childhood, and women who carry such mutations often have to choose between not having children or undergoing in vitro fertilization (IVF) with donor eggs in order to avoid passing on a genetic condition.
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However, researchers from The New York Stem Cell Foundation Laboratory and Columbia University Medical Center may have found a way to prevent inheritance of these disorders with a technique that involves transferring a cell’s nucleus, and not its mitochondrial DNA, into a different human egg.
The research is published in the journal Nature and describes how they team successfully removed the nucleus of an unfertilized egg and replaced it with the nucleus from a donor’s egg cell. This way, the egg cell still has a mother’s genes but not her mitochondrial DNA, which is located outside the nucleus in the egg’s cytoplasm.
By lowering the temperature of the egg before the transfer, the researchers were apparently able to complete the procedure without harming the egg cell. Previous nuclear transfer techniques resulted in damage to about half of the eggs, which either failed to divide or began dividing with abnormalities. In the current study, the scientists activated the egg with the new nucleus, took stem cells from it, and allowed them to grow for a year. They observed the stem cells as they developed into a variety of cell types including neurons and heart cells, which are influenced by mitochondrial DNA.
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“This gives us the opportunity to prevent the inheritance of these devastating diseases,” says the study’s c0-author Dieter Egli. “Because these mutations are inherited in the cytoplasm, it can be unpredictable. But for the first time, we can prevent the mutations and really cut off the inheritance of these diseases.”
Such nuclear transfer is the basis of cloning, and the same technique was used to clone the first mammal, Dolly the sheep, who was a genetic copy of the ewe whose DNA was transferred into the donor egg that became Dolly. Instead of using a fully developed adult cell, however, in the current experiment Egli and his team used the DNA from another egg, which should make the process more successful since both eggs are about the same age developmentally. The fact that the neurons, heart and other cells that developed from the transferred egg suggests that the technique could be a way of bypassing the inheritance of certain mitochondrial mutations.
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But before the procedure can be used clinically, Egli says additional studies need to repeat and perfect this results. And the public needs to become more comfortable with the idea of swapping egg cells, something that may still be too much of a social and ethical hurdle for many. “I think to a large extent [the greatest challenge ahead] is the opinion of people. Can we convince people that we should be doing this now? We need to have a public discussion between patients and providers. We want to start the conversation with this,” he says. And if advances such as these continue, that dialogue can’t happen soon enough, especially for families who are affected by mitochondrial disorders.