Dear Jeanie: What Should I Know About the Gene MTHFR?

Editor’s note: The “Dear Jeanie” blog series uses fictional patient questions written by an NSGC expert based on her experiences as a genetic counselor. This series in no way represents a real patient or single genetic counseling session. 


Dear Jeanie,

Just for fun, I recently did genetic testing with some of my family members.  I only wanted to know more about my ancestry, but my brother downloaded his file from the test into a free program on the Internet and found out that he has a mutation in a gene called MTHFR.  The name of the mutation is A1298C.  I have looked it up online, and it is associated with so many terrible things, like heart disease, autism and infertility.

Since my brother has the mutation, I know there is a good chance that I have it too.  I am 26 and recently married.  My husband and I talk about having kids – someday.  I don’t really want to find out if I have this mutation, but maybe I should.  Maybe we shouldn’t wait if I am likely to have trouble having children.  On the other hand, maybe my husband won’t want to have any children, if there is a good chance they will have autism or heart disease.

This was supposed to be fun, and now I am stuck between a rock and a hard place!  What should I do?


Dear Stuck,

MTHFR is an awkward name, isn’t it?  If you try and pronounce it, it sounds like you are muttering a profanity under your breath, which is exactly what many genetic counselors do when we think about this gene.  It frustrates counselors that MTHFR results end up being so stressful for people just like you, when most of the time there is no reason for concern.  Yes, there are multiple reports showing a statistical relationship between certain variants of MTHFR like A1298C and a whole laundry list of serious medical conditions, but statistics (lies, damned lies and statistics!) can be misleading. 

If you go online, you’re going to see a blizzard of numbers, but here’s the one number that matters the most: 50 percent.  Nearly 50 percent of the people in the United States carry one or two copies of A1298C.  Don’t let the word “variant” fool you.  The A1298C variant is normal.  Your brother has it, and therefore, as you point out, there is a 50-50 chance you have inherited the same gene.  But actually, even if you knew nothing about your brother’s gene, there would have been essentially a 50-50 chance that you carried at least one copy of A1298C.  That’s how common it is.

Something carried by 50 percent of the population can’t possibly be so dangerous that it should make you think twice about having a baby.  That’s not to say that there isn’t some risk.  When they start producing risk-free kids, let me know.  I will take half a dozen.

What you have to understand, Dear Stuck, is that genes, as important as they are, don’t affect everyone the same way.  Just knowing what gene you have is only a part of the puzzle when it comes to thinking about your health.What you have to understand, Dear Stuck, is that genes, as important as they are, don’t affect everyone the same way.  Just knowing what gene you have is only a part of the puzzle when it comes to thinking about your health.  The MTHFR gene is good example: it produces an enzyme that helps reduce the level of the amino acid homocysteine in your body. There are all sorts of terrible risks associated with high levels of homocysteine, including heart attacks, strokes, migraines and recurrent pregnancy loss.  Your level of homocysteine is determined by many things, including your genes and what you eat.  The A1298C variant produces a version of the enzyme that is a little less efficient at doing its job, so some people with that variant do have high homocysteine levels, but most do not.

If you want to know whether you have high homocysteine levels, test your homocysteine levels, not your genes.  It will tell you so much more about whether or not you should be concerned.  If they are high, talk to your doctor.  You can’t change your genes, but there are lots of other things you can do.  In the meantime, Stuck, eat some leafy green vegetables, and go back to having fun!

Best wishes,

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