SciWhys: a cure for Carys? Part Two
Over the past year, the SciWhys column has explored a number of different topics, from our immune system to plants, from viruses to DNA. But why is an understanding of topics such as these so important? In short, using science to understand our world can help to improve our lives. In my last post and in this one, I want to illustrate this point with an example of how progress in science is providing hope for the future for one family, and many others like them.
By Jonathan Crowe
In my last post, I introduced you to Carys, a young girl living with the effects of Rett syndrome. Thanks to scientific research, we now understand quite a lot about why Rett syndrome occurs – what is happening among the molecules within our cells to mean that some cells don’t behave as they should. Simply knowing about something is one thing, though; making constructive use of this knowledge is another thing entirely. During this post I hope to show you how our understanding of what causes Rett syndrome is being translated into the potential for its treatment – a cure for Carys, and the other young girls like her.
In my previous post I mentioned how Rett syndrome is caused by a faulty gene called MECP2 that affects the proper function of brain cells. However, the syndrome doesn’t actually kill the cells (unlike neurodegenerative diseases that do cause cells to die). Instead, the cells affected by Rett syndrome just function improperly. This leads us to an intriguing question: if the faulty gene that causes the syndrome could be ‘fixed’ somehow, would the cells start to behave properly? In other words, could the debilitating symptoms associated with Rett syndrome be relieved?
Obviously, researchers can’t simply play around with humans and their genes to answer questions such as these. Instead, researchers have studied Rett syndrome by using “mouse models.” But what does this mean? In short, mice and humans have biological similarities that allow the mouse to act as a proxy – a model – for a human. How can this be? Well, even though the huge variety of creatures that populate the earth look very different to a casual observer, they’re not all that different when considered at the level of their genomes. In fact, around 85% of the human and mouse genomes are the same.
Now, if the biological information – the information stored in these genomes – is similar, the outcome of using this information will also be similar. If we start out with two similar recipes, the foods we prepare from them will also be very similar. Likewise, if two creatures have similar genes, their bodies will work in broadly similar ways, using similar proteins and other molecules. (It is the bits of the mouse and human genomes that aren’t the same that make mice and humans different.)
In essence, the mouse Mecp2 gene is to all intents and purposes the same as the human MECP2 gene, and has the same function in both mice and humans. Equally, if this gene malfunctions, the consequences are the same in both mouse and human: a mouse with a mutation in its Mecp2 gene exhibits symptoms that are very like a human with a mutation in the same gene – that is, someone with Rett syndrome. In short, mice with a Mecp2 gene mutation are a model for humans with the same mutation.
With all this in mind, if we can learn how to overcome the effects of the Mecp2 mutation in the mouse, we might gain valuable insights into how we can overcome the equivalent effects in humans.
And this is where things are getting very interesting. Researchers have found that the effects of Rett syndrome in mouse models can be reversed. The researchers raised mice in which they had control over whether the Rett gene, Mecp2, was switched on or off. If they left the gene switched off, the mice developed Rett-like symptoms. Intriguingly, though, if they switched the gene back on again the symptoms gradually improved.
Now, this finding is far from being a cure for Rett syndrome – but it does tell a positive story: it suggests that cells that are malfunctioning because of the Rett mutation aren’t irreversibly damaged. Rather, if the mutation can be corrected, cells appear to start behaving normally again – all of which offers the tantalising possibility of overcoming the disease in humans.
The big challenge now, though, is to figure out how to remedy the faulty genes in girls such as Carys. After all, the mouse model is an artificial situation; the mice studied in the research were bred to carry a specially-created version of the gene: the special gene didn’t just occur naturally. The task faced by researchers is akin to being faced with a library full of books, having to find a tiny error on the right page of each copy of the book, and then correct it – all without actually removing the books from the library: they must find the affected cells, pinpoint the faulty gene that’s causing the problems, then somehow fix it – all without affecting the other genes found in those cells (or indeed the genes in other unaffected cells).
It’s not an impossible task, though. I mentioned in my last post how one of the two X chromosomes in females is always deactivated; the deactivated chromosome in those with Rett syndrome can often include a normal, undamaged MECP2 gene. What if this normal gene could be reactivated? Perhaps this could help to ease symptoms of the disease? Such reactivation of genes is something that researchers are beginning to explore in relation to other genes already; perhaps there will be promise for MECP2 too.
Recent years have also seen advances in the field of gene therapy, whereby defective genes in the cells of humans are replaced by normal, healthy ones. However, gene therapy is still some way from being an approved, widely-used treatment option: there have been promising signs on the road to making it a realistic option, yet these have been tempered by setbacks along the way.
Still, the knowledge that fixing the faulty MECP2 gene could lead to an easing of symptoms – as seen in the mouse model – continues to spur on researchers in their quest for a cure for Carys, and others like her. Reason, if you needed it, to live in hope.
Jonathan Crowe is Editor in Chief for Natural, Health & Clinical Sciences in the Higher Education Department at Oxford University Press. A biochemistry graduate, he manages OUP’s undergraduate textbook publishing programme across a range of science and science-related disciplines. He is also an author of Chemistry for the Biosciences, now in its second edition, and was a runner-up in the Daily Telegraph/BASF Young Science Writer Awards (in 2001, when he was still classed as being ‘young’). You can read more about OUP’s science books here.