Carriers

What’s the first thing that comes to your mind when you hear the word “carrier?” Do you think of an aircraft carrier? Maybe the helicarrier from the Avengers movie series?

Copyright Marvel Studios

People who might be more medically inclined will think of disease carriers. These are people who may carry an infection, but not show any symptoms. For example, when Europeans first came to the Carribean and North America, they brought many diseases with them. While the Europeans were not sick, the diseases they carried killed nearly ⅔ of the indigenous populations.

A copper plate engraving of Columbus landing in the Caribbean by Theodore de Bry. Courtesy of the Smathers Library Special Collections

Today, what we’re talking about are genetic carriers. These are people who have a single allele for a genetic condition. For example, sickle-cell anemia is a recessive condition. When someone has one risk allele for sickle-cell anemia, they are resistant to malaria. But when they have to two risk alleles, they develop sickle-cells. These cells cause clotting in major arteries and veins, leading to strokes, thrombosis, and severe pain.

Notice the banana-shaped cells? Those are sickle-cells.

But a carrier would never know that they had one of these risk alleles. They could live their entire life blissfully unaware of the risk allele.

But Then Comes Love (And Sex)

You’ve probably heard the schoolyard rhyme:

“First comes love,
Then comes marriage
Then comes a baby in the baby carriage”

If you’re a carrier, that baby in the carriage could have one of your risk alleles. And if your significant other also has a risk allele, your baby could have the condition. For a single recessive trait, the cross between two carriers has a 25% chance of producing a child who is affected by the condition. It also has a 50% chance of producing another carrier. The mathematics can get complicated if you consider more genes.

It might seem like the condition came out of nowhere. Recessive alleles can hide in the background for several generations. They “skip” generations, so-to-speak.

Let’s Not Forget Ethnicity

Sickle-cell anemia affects certain populations more than it affects others. Specifically, it affects people of Central African descent. But sickle-cell isn’t the only genetic condition that affects a specific ethnicity. Lots of other conditions follow ethnic groups:

• Tay-Sachs Disease and Crohn’s Disease are more common amongst Ashkenazi Jews.
• Cystic Fibrosis is more common for people of Northern European descent.
• Thalassemia is more common amongst people of Mediterranean ancestry.
• Type 2 Diabetes is more common amongst people of Asian or Native American ancestry.

There are many reasons for these differences:

• Some, like sickle-cell anemia, provide a protective effect against a disease (such as malaria).
• Some, like Tay-Sachs or Crohn’s, may be the result of genetic bottlenecking, where only a small portion of the population survived and passed on its genes.
• And still others may simply be a result of poor adaptation to our modern environment and food.

Regardless of the reason, we shouldn’t ignore the fact that some genetic conditions target certain ethnicities more than others.

So What Can You Do?

Now at this point, some of you might be thinking: “Well, crud. I might be a carrier. But how do I know? And what can I do?”

And I’m happy to help you, hypothetical reader! There are many things that you can do:

1. Talk to Your Family
   • While recessive alleles can skip generations, it’s relatively rare for your family to not be aware of them. Your parents or grandparents may know about the conditions that are most likely to affect you.
2. Get Tested (And Get Your Partner Tested Too!)
   • Several genetic services offer carrier status reports. These services can help you learn what conditions you might be carrying. We recommend that you speak with a genetic counselor before taking one of these tests.
3. Lower Your Risk of Passing It On
   • While you can’t control who you are or who you love, there is something to be said for Pre-Implantation Genetic Diagnosis (PGD). Fertility clinics can produce in vitro embryos (AKA test tube babies) and then test their genetics before implantation in the uterus. These genetic screens allow carriers to avoid passing the condition to their children.
4. Choose Not to Have Children
   • While this option is not for everyone, it is a reasonable choice. If you don’t want to pass on a condition to your kids, then you can simply not have kids. However, this is a deeply personal decision, and we recommend talking to your doctor first.

If you have any other tips, please leave them below in the comments!