Some thoughts on genetics

Today’s fact: In 90% of cases of Down syndrome, the extra chromosome comes from the egg, rather than the sperm.

Let’s start with a little back story. I don’t know how much of this I’ve told (if any) and if I have ever written about it it was probably a long time ago. Anyway, way back in 2007 when my sister Kirsta was pregnant with Patrick (her first) she got a blood clot. Obviously blood clots are serious business, so she got a complete blood work up to find out if she had any clotting disorders. Turns out the answer was yes, two of them. Factor V Leiden and a homozygous MTHFR mutation. I was also pregnant at the time, so I had testing done to find out if I had either of these conditions. Yes to both.

Now, Factor V is a simple clotting disorder. One copy of the gene (heterozygous) means you’re at higher risk of a blood clot than the general population, two copies (homozygous) means an even higher risk. I am heterozygous for Factor V. (Weirdly enough, so is Brian, so we were familiar with it before I was even tested.) My doctor recommended a “can’t hurt might help” daily dose of baby aspirin.

MTHFR (methylenetetrahyrofolate reductase) is more complicated. It can contribute to blood clots, yes, but that’s sort of a secondary issue.  (Also, in this case, only people with a homozygous mutation are affected.) In short, an MTHFR mutation affects the way your body processes folic acid. This means the normal amount of folic acid isn’t enough. To combat this, my doctor recommended I take 4 mg a day in addition to my prenatal vitamin. Over the counter, folic acid comes in 800 mcg tablets. So I took 5 of those a day. (Getting enough folic acid is very important during pregnancy, in case you are unfamiliar.)

I’ve continued my daily aspirin and folic acid supplementing with every pregnancy. Generally as soon as we’re trying I start taking them again. And I’ve never had a problem with blood clots.

However. I recently read something interesting. A quote from the March of Dimes website, “Some studies suggest that women who have certain versions of some genes that affect how their bodies metabolize (process) the B vitamin folic acid may be at increased risk for having a baby with Down syndrome.” Women like me, with an MTHFR mutation. And because the extra copy of chromosome 21 is present at conception, folic acid during pregnancy makes no difference. (To Down syndrome. There are other reasons to take it during pregnancy.) Anyway, there’s no epiphany or anything here, I just find this kind of information fascinating.

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6 thoughts on “Some thoughts on genetics

  1. SUPER interesting. I’m such a science geek and I find genetics totally fascinating too. I have another layer of interesting genetic “happenings” in my reproductive history but I haven’t decided yet whether it’s something I want to blog about (ironically, I wouldn’t mind sharing with internet strangers but I haven’t talked to my family about it).

    I like your Fact of the Day idea!

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