By Grant Jacobs 03/08/2017


Widely reported today is the research paper by an USA team who edited a gene that causes sudden heart failure in young adults.

I’d like to take a different approach, briefly raising just two things that nagged at me while reading this work.

Before I do be clear there are real technical advances reported.* I’m not denying or opposing them.

It’s just that when I step back a little I have some questions. These questions include the sort of questions that a discussion about the use of embryo editing might want to have.

There are methods to screen embryos before they are implanted, to try eliminate ‘defective’ embryos. (Similarly, there are some ways to try increase the number of ‘good’ embryos.)

Without any gene editing about 50% of the fertilised embryos used in the study would not have the mutation, about a half of them would be ‘normal’. What the gene editing does is increases the number of eggs available for use that are free of this mutation from about 50% to about 80%.

If this were to be applied it mean there would be more ‘good’ embryos to pick from. You have more positive cases, but you’d still want to be screening the embryos.

A question I have is to what extent would embryo screening where 50% of the embryos are ‘good’ would have been enough to ensure an implanted embryo would be free of the mutation without gene editing?

I know don’t much about pre-implantation embryo screening—it’s not my thing so I can’t take this further than ask the question—but it would be a key question to ask.

I see little discussion of this in media reports I’ve seen so far. The paper is focused on the technical aspects of the work itself, rather than it’s context. The accompanying News and Views piece mentions it briefly only in the final sentence. While most media reports I’ve seen don’t discuss this, a piece at Scientific American does.

Another thing that raised questions for me is that, thus far, the gene editing approach used looks to be limited to where the father’s sperm has the mutation, but the mother’s egg does not. It might well also apply to the reverse situation where the egg carries the mutation and the sperm does not. Time will tell, and no doubt this will be tested.

What looks unlikely is where both parent’s gametes carry the mutation. That’s a potential stumbling block as you’d think the more compelling argument for gene editing would be where both gametes have the life-threatening mutation, and hence all fertilised embryos would have the mutation. The approach used does poorly in that situation, and it’s possible it may prove difficult to do.

Part of the success of the approach turned out to be relying on a ‘good’ copy of the gene being present in the egg’s DNA that could be used as a template for the cell to replace the removed defective portion from the sperm’s DNA.

In the case of both parents having a defective gene, there is be no ‘good’ copy for the cell’s DNA repair for work from.

Post-amble

Now that I’ve seen it, other experts commenting on the work have raised the same issues. (At least that means I’m in good company?) It would be good if media accounts would follow suit. In that light, it’s worth noting the that publisher’s press release (which I did not have) in part raises the first point.

These are only initial thoughts, but I hope they encourage discussion and an interest in what is happening.

Footnotes

* You’ll notice I haven’t given a detailed explanation of the work. I could break this down in a later post, but for now I want to just raise these initial thoughts without bogging them down in too much detail. I’m taking this approach in part because I haven’t been able to come to this story sufficiently ahead of time to write the longer piece I might have pitched elsewhere.

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Haemophilia — towards a cure using genetic engineering

Human gene editing recommendations from USA science panel

Gene editing and GMOs in NZ, part three (there’s links to parts one and two at the start)

Food and genetic modification: better informed policy and legislation wanted

Featured image

DNA damage repair, featuring DNA ligase (coloured). Public domain, from Wikimedia Commons. The final steps of gene editing rely on the cell’s own DNA repair mechanisms. These are essential to keeping our genomes in good shape. DNA ligase repairs breaks in DNA strands by joining them together.