What can you do if you’re a genetic carrier?

In my last post, I talked all about what is means when you are a genetic carrier of a recessive gene.  To recap, the recessive gene will not cause disease, but your partner also has that recessive gene, you may have a child with a disease. Let’s think about the options, using a capital letter (G) as the normal gene and a lower case letter (g) as the recessive mutated gene.

carrier-noncarrier youandpartnercarrierIf you are a carrier, you’re have one copy of G and one copy of g (or Gg).  What if you have a child with someone who isn’t a carrier (GG)?  If you look at the possibilities (to the left) you have a 50/50 chance of having a child who isn’t a carrier or one who is.  But you will not have a child who has the disease.  On the other hand, if both you and your partner are carriers (see the picture on the right), you have 25% chance of having a child who isn’t a carrier, 50% chance of having a child who’s a carrier, and 25% chance of having a child who has the disease.

If you’re a carrier and your partner is a carrier, you know your odds.  So what are your options?  Before I start, if you’re dealing with this personally, please discuss all of this with a trained medical professional.  I can explain the biology of why things happen, but only your doctor can give you medical advice and treatment options.  Also, these decisions are all personal to you.  There is no one answer, and what works for you may not work for someone else – and this is often what we face when making these very personal medical decisions.

CVSOptions:

  • If you know that you and your partner are both carriers for a particular disease, you can choose not to get pregnant and avoid the risk altogether
  • Alternatively, you can get pregnant and  monitor the pregnancy closely.  Go ahead and roll the dice!  There is a 25% chance of having a child with that disease and a 75% chance that they won’t.  Having the knowledge in advance, you will know the likelihood and can monitor the pregnancy accordingly
  • There are tests like chorionic villus sampling  (CVS) that can test for genetic diseases (such as Tay-Sachs disease) before birth, if both you and your partner are carriers for a recessive gene that causes disease
  • If the developing child is found to have a genetic disease, depending on the disease and severity (e.g., if they will or will not survive at birth), there is the option to terminate the pregnancy. There also may be options for treatments while the child is developing or immediately at birth that may help decrease the severity of the disease right away.
  • You can choose instead to use a sperm or egg donor from someone who doesn’t carry that recessive gene.
  • You can use in vitro fertilization and check the genes of the embryo pre-implantation to select those that do not have two copies of the recessive genes.
  • Choose to adopt

As an aside, I asked my primary care physician about carrier testing a few years ago.peopleDNA  Without a family history of any genetic diseases, she was resistant (if not downright hostile) about me wanting to get carrier testing, and mentioned that insurance likely wouldn’t pay for the testing.  I’m hoping that my experience was not the norm, however, I don’t think that most primary care physicians have a deep understanding of genetics and genetics diseases and may be uncomfortable suggesting this type of screening because they would not know how to best interpret the results.  Interestingly, a number of companies now exist that will perform the carrier testing for you for a nominal fee, such as Pathway Genomics, Counsyl, and Natera.  I cannot recommend or discourage you from using or not using these services, however you generally need to work with your doctor to order these tests.

Again, these are all options, not medical advice, and all up to you as to what works best for you and your partner.  But with the knowledge of what may happen and why it may happen, you are at least armed with information to ask meaningful questions about yours and your non-existent child’s potential genes before or during your pregnancy,

What does it mean if I’m a “carrier”?

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.

cfLet’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.
youandpartnercarrierThere 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.

carrierSo 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.