Other Genetic Principles

I once read that Propecia works by means of gene transcription. What does this mean? Can Propecia alter a person's genes?

-A curious adult from Texas

May 3, 2007

This is a great question! It really gets to the heart of how our genes work and how medicine affects them.

You're right. Propecia affects gene transcription. This means it alters how genes are read. But not the genes themselves.

In fact, many medicines work by affecting gene transcription. You've probably heard of some and didn't even know it. Like estrogen.

Many women take estrogen as part of their birth control. Or to treat symptoms of menopause like hot flashes and osteoporosis.

Propecia, on the other hand, is commonly used to treat baldness. Sometimes it helps hair re-grow. But there's a catch.

If you stop taking Propecia, the new hair you've grown goes away again. Why? Because Propecia doesn't permanently alter genes.

To understand this, let's review what genes are and how they work. Humans have 25,000 genes.

Each gene is a set of instructions for something different. For example, we have genes to make our eyes brown or green or blue (or lots of colors in between). For more information, click here.

How does a gene make your eyes brown? Or blue? With proteins.

When each gene's instructions are read, a protein is made. It is this protein that does the work of the gene. For brown eyes, the protein makes lots of the pigment melanin in the front of the iris of your eye.

Making a protein is a lot like making a car in a factory. To build each car, we need a set of instructions. And from those instructions, we can make the cars -- the Prius, Camry, or Corolla.

Each car's instructions are like our genes. And the cars themselves, the Prius, Camry, or Corolla, are like our proteins.

When a gene's instructions are read to make a protein, it's called gene transcription. This process doesn't change a gene at all. Why?

Because each gene needs to be read over and over again. So the protein can be made over and over again. This couldn't happen if a gene were altered during gene transcription.

When you pick up the car instruction book and read it, you don't alter the instruction book. You can still read the book again later. And make the car again if you need to.

It's the same way with genes. By reading a gene, the body gets information from the instructions in that gene. But leaves the gene unaltered so it can read it again later.

Also thrown into this mix of genes and proteins are enzymes. Enzymes speed up everything that happens in a cell. We have different enzymes that do different things.

Thinking back to our car factory, enzymes are like the machines in the factory that assemble the cars. Sure, we could have a bunch of people put the cars together themselves. But that would take a long time. So we have the machines, the enzymes, speed up the process by putting the cars together for us.

We have an enzyme that helps speed up gene transcription. It's called RNA polymerase. If we didn't have RNA polymerase, reading our genes would take forever!

How does this all relate to Propecia? Propecia slows down or stops gene transcription for genes related to balding. But it does so in a roundabout way.

One of the proteins that helps read the genes involved in balding is something called the androgen receptor (AR). The AR helps with many things in the body. Like developing male sex characteristics. Or growing larger muscles. Or growing taller. Or...

We can think of the AR as one of the robots involved in making a car. To work, robots need power.

The AR needs something to work too. That something is a strong form of testosterone called DHT. Without DHT, the AR doesn't work as well.

What Propecia does is keep our bodies from making DHT. It unplugs the robot. Now the car can't get made. And the gene isn't read.

But if we take away the Propecia or plug the robot back in again, both will work fine. That's why the effects of Propecia are reversible. Because the genes it keeps the cell from reading aren't permanently altered.

What you read was right. Propecia affects gene transcription by preventing DHT from being made. But affecting gene transcription doesn't alter the genes themselves.

Amy Radermacher, Stanford University

Reading a gene does not change it.

Making a protein is a lot like making a car.