The proliferation of news related to genetic modification has rescued from exile some disturbing questions that the pandemic seemed to have left in torpor.
For example: Will we ever see births with a la carte traits, such as eye color?
The recent release of He Jiankiu, the scientist responsible for the experiment that gave rise to the first genetically modified human beings, has probably contributed to awakening some dormant ghosts.
The quick answer is that, as this scientist demonstrated in 2018, changing genes is already technically possible, but it is prohibited.
In addition, the tools used still show certain limitations and most of the genetic modifications that we can produce are still inconspicuous.
For example, this scientist genetically modified a fertilized egg by removing from its DNA the instructions for manufacturing a molecule in our body whose name may not tell us much, the CCR5 protein.
From this experiment a pair of twin girls were born unable to produce that molecule forever in any of their future cells, including their own eggs.
Therefore, the important thing is that when one of these twins reproduces, their body will produce children who will also receive a copy of the genetically modified DNA.
This will mean that the innovation that He Jiankui introduced in the twins will be inherited.
In that case, it will be the first time that an artificial genetic modification has passed from one generation to the next.
This is precisely what international law prohibits almost unanimously.
The laws of most countries consider that it is too early for laboratory genetic changes to become transmitted and form part of humanity's hereditary heritage.
By contrast, genetically modifying cells from a developed individual for therapeutic purposes is not prohibited (at least not universally).
The reason is that genetic changes that are introduced into, for example, the blood, liver or lung of an adult will die with the individual, not be passed on to their descendants.
Is preventing the spread of an artificial genetic change the only reason these types of experiments are regulated?
No, the overwhelming majority of the scientific community considers that gene editing techniques, such as the well-known CRISPR-Cas9, are still too complex and novel to be worth further testing before applying them.
After all, gene editing involves cutting and pasting, putting in and taking out, fragments of DNA inside tiny cells;
the researchers' goal is to master the tools so that they can ensure that only the planned modification will be executed.
A small mistake could damage other parts of the DNA, leading to harmful mutations and disease.
And when the process is mastered will it serve to repair any genetic disease?
No, although abundant encouraging results have been presented, there is a determining factor that conditions its implementation.
Let us think, for example, of our hearts.
This, like any of our organs, is made up of billions of cells.
It is useless to try to get to all of them a correct copy of the gene that you want to repair or eliminate in an adult.
This difficulty, precisely, is what can be solved by modifying a recently fertilized egg.
Editing the DNA before birth is the only viable way to ensure that the repair will reach every cell in the body.
So, genetic modification in patients is not efficient except in certain organs and types of cells with particular characteristics,
Will traits like eye color be able to be changed when the procedure is legal on eggs or embryos (if it ever is)?
Maybe yes, but there are likely to be surprises.
Traits, such as eye color, are determined by several dozen genes that make a small coordinated contribution.
Today it would be impossible to modify all of them due to the technical difficulty involved, although it will probably be feasible in the near future.
In any case, genetics is very complex and we will have to assume that these genes participate in many other processes within the organism, so altering them will have consequences beyond eye colour, for example, in tissues such as hair and skin.
On the other hand, regardless of the interest capricious decisions such as choosing eye color,
the presence of most traits is also modulated by environmental factors.
For example, height depends on several hundred genes and that only determines a part of the final result, which is also determined by diet, state of health, and so on.
A large investment and amount of knowledge will be necessary to even consider it, will it be worth it?
To finish presenting the panorama, it should be added that the gene for the CCR5 protein that
He Jankui removed from the twins' DNA is the cellular receptor that the human immunodeficiency virus (HIV/AIDS) uses to enter and infect our white blood cells.
That is, the objective of the experiment was to produce the first humans without a receptor and, therefore, immune to AIDS created by genetic modification.
It is not very clear what secondary consequences this change has, but it is undoubtedly a change of great clinical impact obtained by modifying just one gene.
It is indisputable that, despite the difficulties and the road that remains to be covered, the potential of the technique is remarkable.
In addition, we must be aware that the same procedure can have applications of interests as disparate as removing a future disease from an embryo or satisfying the whims of some parents.
Miguel Pita
is a researcher and professor of genetics at the Autonomous University of Madrid.
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