What does it mean when someone “carries” anything? The definition of “carry”is to hold or support something while moving somewhere. Often when you carry something it’s heavy, a burden. When you’re a genetic carrier, it’s much the same. You’re holding or supporting a recessive gene mutation as you move around in your normal everyday life. Even though the recessive gene doesn’t affect you, it’s a genetic burden, because you could pass the trait down to your child.
Let’s remind ourselves what it means to have a recessive gene (or re-read the original post referencing 50 Shades of Grey). You have two copies of every chromosome, and on each of these chromosomes is copies of each gene (called alleles – pronounced AL-eels). These genes can be slightly different. In some cases they are different enough that one copy doesn’t work as expected or work at all (these are the “recessive” genes we talked about in an earlier post). Often the functional copy of the gene can compensate for the copy that doesn’t work right. But in the case where both copies of the gene don’t work correctly, the person can end up with a disease. The example that we used previously was cystic fibrosis. A person will have cystic fibrosis only when the have two copies of the mutated CFTR gene. The same is true for sickle cell anemia, which is caused by having two mutated copies of the hemoglobin gene called HbgS. If a person only has one copy of HbgS, the other normal hemoglobin can produce enough hemoglobin to function just fine. However, if there are two copies of HbgS, the HbgS protein structure collapses in cases where the person doesn’t have enough oxygen and this causes the red blood cells to make a sickle shape.
There are a number of diseases that are caused by having two copied of a mutated recessive gene (many are listed here). But again, if you only have one copy, you’re just fine – but you carry that gene mutation. If you have children with someone else who is a carrier (meaning that they also have one copy of a recessive gene that would cause disease), then you have a 25% chance of having a child with that disease, because they have 25% chance of getting two copies of the recessive gene.
This isn’t a huge deal – only 25%, right? Except that you would never know from looking at someone if they are a carrier. And you wouldn’t know from living with yourself for all these years if you are a carrier. And some populations or ethnic groups are more likely than others to be carriers for recessive genes for certain diseases. If you look at the chart below, I have listed a few ethnic groups and diseases which they are often genetic carriers. After the name of the disease, I have listed the likelihood of someone from that ethnic group being a carrier for a recessive gene that would cause that disease. For Caucasians, if you and 28 people are sitting in a room, one person would carry a mutation in one copy of the CFTR gene that would cause cystic fibrosis. It is estimated that at least one in five Eastern European Ashkenazi Jewish individuals is a carrier of one gene that would cause a genetic disorder.
So what should you do now that you know that you could be a carrier for gene that could cause a disease. There are options – the first one being doing nothing at all. You could also look at your family history. Are there people in your family or your partners family with a recessive genetic disease like Wilson Disease or Tay-Sachs? If so, you may want to get tested for common recessive genes. On the other hand even without family history, if you are from a particular ethnic group such as Ashkenazi Jew, you may be encouraged to get tested no matter what (see an interesting guidance about this here) before or during pregnancy. There is also the possibility that you want to be prepared, and before you and your partner get pregnant that both of you are tested for common carriers. Next post, we’ll talk more about what you can do if you are a carrier.