X-Men are mutants. So is Dr. David Banner, who turns into the Incredible Hulk. And the Joker in Batman is a mutant (along with most of the other villains in Batman). So many superheros and supervillains are considered mutants that the word MUTANT has come to mean something a little terrifying.
Before we start talking about diseases that are caused by gene mutations, it’s important to really understand what a mutation is and how it’s not necessarily terrifying, and won’t turn you into Wolverine or The Hulk.
A mutation is a change in the DNA. Change is such a broad term, but it’s broad because the DNA can change in a lot of different ways. One nucleotide of DNA could be replaced with a different nucleotide, a nucleotide or several nucelotides or big long stretches of nucleotides could be removed or added (this is called a deletion or insertion), pieces of chromosomes could be moved from one place to another (or switched, which is called a translocation), or pieces of DNA can be duplicated (this includes whole genes being copied, which is called an amplification).
What actually happens when there is a mutation in your DNA? Let’s first remind ourselves of what DNA does – about 2% of the DNA codes for proteins and the other 98% either does nothing (that we know of) or regulates the DNA. So when there is a mutation, the mutation may be in a gene or it may not. And it may affect the protein or not. So in terms of changing a trait or causing a diseases, sometimes it may do this and sometimes not.
So let’s talk about when mutations are good. Mutations that happen by chance are what’s responsible for evolution. For example, without genetic changes, humans wouldn’t be able to drink milk. We’d still all be lactose intolerant since a mutation in the gene that allows us to metabolize milk allows us to process milk as adults.
There are also mutations that are neutral or have no noticeable affect. These could be in places in the genome that don’t contain genes or regulate gene expression. They could also be mutations that don’t change the 3D shape or function of a protein. So even though the DNA is different, the protein isn’t affected.
But what about when the protein is affected? Mutations can decrease the activity of a protein, increase the activity of a protein, change the amount of protein (making too much or too little), change the function of a protein, or remove a protein altogether.
As an example, let’s think about what would happen if we changed the function of a protein that was responsible for telling cells to grow and divide. Usually, the protein would be turned on only if it received the proper signal, and then it would grow and divide. If there was a mutation that make this protein always on, then the cell would grow and divide uncontrollably – like having a broken copy machine that keeps copying even though you didn’t want it to. Sound familiar? This is one of the ways that mutations can cause cancer, by turning proteins on that make the cells copy themselves when they shouldn’t forming a tumor.