“She has the breast cancer gene.”

“He carries the cystic fibrosis gene.”

“He got the muscular dystrophy gene from his mom.”

When talking about genes, we often use this kind of language. The gene for [blank] disease. We speak about these genes as if they were rogue agents, inserting themselves in your genome and wreaking havoc. But this isn’t entirely accurate, and frankly, it gives our genes a bad rap. In everyday speech, it doesn’t make much of a difference, but it does if you’re trying to understand the genetic basis behind a condition.

Photo of chromosomes (complete set of genes)
The Chromosomes of Some Dude

To understand what I’m talking about, lets start with the basics. If you look at your DNA under a microscope, you’ll see it packaged into structures called chromosomes. We have 23 pairs of chromosomes; one of each copy comes from Mom, the other from Dad. Each type of chromosome has it’s own set of genes. Since we have two copies of each type, that means we have two copies of each gene. Genes are strings of DNA that are instructions for proteins. The instructions are written in a 4 letter code (A,T, C & G) that your cells can read and use to make the proteins they need. These proteins are responsible for just about everything that happens in your body. Some are used to grow your bones, some give your hair it’s color, some build your red blood cells, and so on and so forth.

So, why is saying “the breast cancer gene” wrong?

Let’s take the most well known “cancer gene,” BRCA1, as an example. BRCA1 is a gene that is contained within chromosome 17. Everyone who is born with two complete copies of chromosome 17 (which is just about everyone), also has two copies of BRCA1. We all have this gene. Two of them, in fact. This gene is the recipe for a protein that is involved in keeping your cells from growing out of control. We call it a “tumor suppressor gene,” and this one is particularly important in breast and ovarian tissues. If at least one of those copies of BRCA1 is written properly, your breast cell makes this protein and is protected from becoming cancerous. But if those copies have a typo, or a “mutation,” in them, that cell either makes a protein that doesn’t work, or doesn’t make any protein at all. That can mean bad news for that cell.

How do mutations happen?

Each and every new cell that is made in your body needs it’s own copy of DNA. Try copying anything 30 trillion times and see how many typos you make. Plus, lots of things damage your DNA: pollutants in the air you breathe, carcinogens in the food you eat, UV rays from the sun, plain ol’ oxygen. With all those threats to our genes, it’s a good thing we have a back up copy of each of them. But, actually, some people don’t. If someone was conceived with a typo in one copy of BRCA1 that keeps it from making that protein, they’re at a disadvantage from the start. Every single one of their cells will be dependent on that one remaining “good” copy to make this protective protein. If something damages the good copy, that cell can now grow out of control and become a tumor. Because of this, people born with a mutation in this gene have a much higher risk of breast, ovarian and a few other cancers than the average person.

So, it’s not that someone has an extra “breast cancer gene” that’s going around giving them cancer. It’s that they have a mutation in one of their tumor-suppressor genes that keeps it from functioning properly, and that puts them at a disadvantage when it comes to breast cancer protection. But no one is going to say that mouthful when talking about what’s going on with their friend.

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