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Photo: Thomas Hawk

Where them genes at
Where is the DNA in a human cell? The first answer that comes to mind is “in the nucleus”. But that is not fully correct. In humans, although nuclear DNA encodes about 36,000 genes, there are 37 genes (≈0.1% of the total) that are encoded somewhere else, inside some sneaky little organelles called mitochondria.

There are many mitochondria in each cell, which produce over 90% of the cell’s usable energy and participate in many cellular processes. As we know, they contain their own tiny genome, but they still depend on the nuclear genes to work properly. Their genetic information (mtDNA) only affects mitochondrial function. They also divide on their own, just like cells do (Legend has it that they used to be bacteria that got into a cell, found it comfy, and stayed), and when the cell divides, the mitochondria are shared among the two daughter cells.

Bam! Mutation
A mutation in the nuclear genome can cause disease. Some are more severe than others, and most of them occur in specific organs or tissues. But since mitochondria are in basically every cell and are pretty freaking important, when a mutation happens in mitochondrial DNA, the consequences can be very bad. Pathogenic mtDNA mutations can cause a wide spectrum of multisystemic debilitating and even deadly diseases. They affect an estimated one in every 5000 people worldwide.

Another important peculiarity is that, when fertilization happens, only the egg’s mitochondria will stay in the embryo. Therefore, you could only inherit an mtDNA mutation from your mother. MtDNA diseases are present in families through the generations, affecting children according to the percentage of “sick” mitochondria they get from their mum.

Excuse me, could I borrow your mitochondria?
If a couple wants a baby, and the mother’s family has a known mtDNA mutation, the risk of the baby getting a mitochondrial disease is very high. With that comes a very difficult life and a high chance of early death.

After a long battle to get the necessary permissions and work on the technique, a research group at Newcastle University devised a way, using in vitro fertilization, to obtain an embryo that contains the same nuclear genome a normal fertilization would yield (23 paternal and 23 maternal chromosomes), but with the mitochondria (and in them the mtDNA) of a healthy donor.

The process is surprisingly simple:
The mum’s egg is fecundated with the dad’s sperm as in a normal in vitro fertilization. Then the nucleus of this new embryo (which carries the information that will be used by the cell to generate the new baby) is inserted into the donor’s egg, whose nucleus has been taken away. The result is an embryo with the full parental nuclear genome, but healthy mitochondria. In other words, mum will have in her womb the same baby, but healthy, thanks to what can be considered a particular organ donation, an organ(elle) donation.

Image by: Juan Landoni

While this is amazing news for families that suffer from these diseases and a huge step for modern medicine, there are groups of people who oppose the technique for several reasons.

Richard, they’re modifying babies! They’ll choose the eye colour soon!

With new techniques, new big debates arise. Ethical debate is very important before making any decision on biomedical legislation, but do we really know what we’re talking about when we debate?

Answering Sarah, who is screaming the news to Richard from the living room, nobody is choosing any perfect baby or changing anything in the baby’s nuclear genome. The procedure is very specific and so is the law that approved it. Neither the nuclear nor the mitochondrial DNA sequence is modified during the process, and mitochondrial DNA does not affect physical appearance.

This procedure not only stops the baby from having the mitochondrial disease, but also solves the problem for the next generations in that family, since the mutation is now gone.

The press has called it a “Three-parent baby”. That’s a very polemic name. Can we really consider the egg donor another mum, or isn’t it more logical to call her a mitochondrial donor whose contribution prevented a horrible disease in a baby?

What is more ethical, accepting a technique without any proven risk in order to save the lives of hundreds of families and their future children who have been going through enormous suffering for generations, or refusing the technique and literally letting their future children suffer and die just because “what if designer babies come next?”.

Juan Cruz Landoni is a chemistry student and an undergraduate researcher in molecular neurology at the University of Helsinki. He's also a Millennium Youth Camp alumnus, a proud nerd, Ravenclaw and a part-time shooting star hunter.