What in the world is “gene editing”?
Well, let’s start by imagining you’re using a word processor to write an essay. When you finish writing, you read back over it to catch mistakes, and you notice that you misspelled a word or you need to add a little more supporting evidence to your argument in paragraph three. So you position the cursor accordingly, click, then make deletions or type new letters and words.
Now let’s translate this from essay editing into gene editing. Instead of 26 alphabet letters, you now have 4 DNA alphabet letters (A, T, C, G) that represent nucleotides, the building blocks of DNA. Instead of making up words and sentences, these different letter combinations make up genes. Sometimes our DNA contains spelling errors, which can arise naturally during replication or can be induced by mutagens such as oxidative damage and exposure to UV radiation. There are many different kinds of “spelling errors” that DNA can have—sometimes a nucleotide is swapped for a different one (this is called a single-nucleotide polymorphism, or SNP), sometimes it is erroneously deleted, sometimes an extra one is added, or sometimes a whole paragraph can just be copied and pasted where it’s not supposed to go (these regions are called transposons). Sometimes these errors don’t make much of a difference, just like it doesn’t matter whether you spell the color between black and white as “gray” or “grey”. However, often the error can turn a word into a completely different word if it’s not corrected.
For example, UV light can cause adjacent thymines (Ts) to bond with each other, among other combinations (see image at right). Going back to our writing metaphor, this might be like adding an unnecessary hyphen in the middle of a word, or joining two words into one. Of course, while your readers might still understand if you write “alot” instead of “a lot,” this mutation can completely change the function of your gene. Fortunately, our bodies have built-in spellcheck in the form of repair enzymes (the ones that fix UV damage are called photolyases). However, just like Microsoft Word spellcheck, our cells don’t catch every mistake, so you should still make sure to wear sunscreen and eat some antioxidants now and then.
Errors that sneak through proofreading are the culprit behind genetic disorders. One example of such a disorder is Sickle-cell anemia (see picture at left), a blood disease resulting from a mutation in the gene that encodes hemoglobin (the protein that carries oxygen), which causes the hemoglobin proteins to stick together, forming fibers that change the shape of the blood cell they occupy. Other diseases caused by a mutation in a single gene include Cystic Fibrosis, Huntington’s disease, Duchenne Muscular Dystrophy, and more.
Now here’s the good news:
Researchers and doctors are now using a variety of gene editing techniques not only to fix harmful DNA errors, but also to alter certain genes to make them work better than they do naturally. Let this sink in for a minute: humans now possess the technology to edit our own DNA. It’s like something you might read in a science fiction novel, but in fact is totally real. It’s science nonfiction.
Now, this is scary in some ways, yes (and we’ll discuss the ethical implications next time)–but it’s also really awesome. This technology has already helped people with Sickle-cell anemia, HIV, and “Bubble Boy” disease, among others.
In my next post, I’ll write about the techniques that researchers and doctors are using to edit people’s genes, as well as the specifics on what gene therapies are already being used successfully in humans. I’ll also talk about the diseases that researchers are currently making progress toward curing with gene editing. Thanks for reading, and don’t forget to follow SciCrazy so you’ll be notified when the next post is up!
Discussion Topic: What’s a disease that you would really like to see cured in your lifetime?