Genetic Treatments and CRISPR

My son's hearing has effectively been restored through the use of cochlear implants, and with great success so far. However I have often wondered if it would ever be possible to fix the underlying biological problems that cause the hearing loss. There is some research being done to see if gene therapy could be useful for this.

Gene therapy is where you go in and alter the DNA within a cell, to fix whatever ails it. This can either be 'knocking out' or switching off a faulty gene, replacing a gene with a healthy version, or introducing a new gene into the cell. As you can imagine, how this is done is pretty complicated and to date has been very difficult.

First off, it's no use changing the DNA of one cell. If we are trying to repair Connexin genes, you'll need to do it to a good chunk of cells in the ear - i'm guessing millions. And you want it focussed. There's no point in sending new Connexin genes into my shoulders, knees or bladder. You any as well be pissing them away, and you might actually do damage.

So you need a delivery vector. This is usually a modified bacteria or virus, which are very good at spreading themselves around specific parts of the body. But you don't want your immune system attacking the delivery vector, so you need to be careful about what you use. And you don't want the new gene going into the wrong part of your DNA - it might split another gene, causing major problems.

Because of this complexity, there are not many gene therapy treatments out there that are in use. That may be about to change however, due to something called CRISPR. This new technique allows us to neatly cut out bits of DNA we don't want, and replace them with ones we do. I'm not going to go into how it works exactly. I will however link to this snazzy (if somewhat lacking-in-content) video.

 One thing I find really fascinating about CRISPR is where it came from. The technique for cutting out specific bits of DNA evolved in bacteria. They used it to defend them against viruses - scientists just had to tweak it a bit.

Viruses don't reproduce by themselves. They get our cells to do it for them. They inject their DNA and it becomes part of that cells chromosome. Our cells own reproduction process then copies it, until the cell is full of virus DNA and literally bursts, releasing more viruses. Bacteria and viruses have been fighting against each other for billions of years (probably), and this evolutionary pressure has given some bacteria a useful tool. They are able to recognise 'foreign' DNA. They then copy it and strap it on to come chemicals. If the chemicals find other DNA that matches, they destroy it.

This was first noticed by yoghurt scientists, trying to see how bacteria used in fermentation defended themselves. Scientists have added to it by getting the chemicals to replace the destroyed DNA with DNA of their choice. I've no idea how.

The explanation above is a massive oversimplification, and as it may be clear I don't fully understand the technique. But there is tonnes of stuff online about it, and it all suggests that this is going to be a revolution for genetic treatments. It has already been used to edit DNA in some animals, and has actually been used to cure a rare genetic liver disease in mice. Some of the scientists behind it were tipped to win a Nobel prize in Chemistry in 2017, but it didn't happen. The law case over patents and who actually developed the technique probably didn't help.