Thursday, January 20, 2011

Your Twins Are Not Semi-Identical

Mary-Kate and Ashley OlsenWikipedia's twin page contains a section about "half-identical" or "semi-identical" twins. These are twins, who instead of sharing half their DNA (like fraternal twins or other siblings) or all the DNA (like identical twins), share three-quarters of their DNA.

There are two popular explanations for this.  The first involves "polar bodies" which are produced during cell division in human eggs and generally discarded during the body.  In this scenario, the polar body ends up being fertilized by a different sperm and producing one of the twins -- identical on the mother's side, but different on the father's side.

The other explanation involves two sperm fertilizing one egg, which then divides in such a way that both resulting embryos are "normal".  Again, you would get the same genes on the mother's side, but different ones from the father.

Some twin books treat the existence of such twins credulously.  For example, Double Duty hedges, "There's growing speculation surrounding a third twin type called semi-identical or half-identical twins, as well."  The Everything Twins, Triplets, And More Book says, "it can provide a tidy explanation for fraternal twins with a strong resemblance." Both books use the Olsen Twins as an example.

Here's the thing.  Returning to the Wikipedia page, it only cites two known examples of half-identical twinning --- one of each type referenced above.  In one case, one twin didn't survive, in the other, one twin was a hermaphrodite.  So chalk these up to "theoretically possible, but not something you wish for your own twins."

I have another tidy explanation for fraternal twins with a strong resemblance -- they're siblings!  Haven't you ever seen siblings who are the spitting image of each other when adjusting for age?  (E.g., you have to check the date on the photograph to figure out which kid it is.)  Well, with twins, you don't have to adjust for age!

I think another reason for the popularity of the semi-identical meme is parents of identical twins who are looking for explanations for their twins' differences.  The National Geographic DVD In the Womb: Identical Twins gives an extreme example, but environmental differences as well as different expression of the same genes will produce differences in any pair of twins.

So instead of indulging parents' belief that their twins are some super-rare third type of twin, twin parenting books should level with people.  Unless you have a medical journal proving your point, your twins are "just" fraternal or identical.  But cheer up --- they could still turn out to be worth $100 million.

Wednesday, January 19, 2011

Twins: Another Reason for Insurers to Mess up Your Claims

When reading Twins! Pregnancy, Birth and the First Year of Life, I was surprised at the following exchange (in one of the "parent discussion" sections):
JOAN: Our insurance company stopped paying on one of the babies because they kept asking, "Why are you sending one baby to the doctor twice in one day?"
LAURA: Our insurance company kept complaining that we were submitting duplicate charges.
NICK: It is mass confusion since the boys were born five months ago. It is amazing that insurance companies don't comprehend twins.
At the time, I found it hard to believe -- twins are not exactly a rare phenomenon.  How could insurance companies be taken aback?

Fortunately, we have not had any denied claims yet; in fact, the insurance company just forked over a large chunk of cash to pay for the boys' NICU stays.  For that I am grateful.  However...

If I go to my insurer's web site and search pharmacy claims for either boy, I get results for both of them.  Clearly, they have programmed their search function to key solely on date of birth.  Of course that doesn't happen for medical claims...

For that, I only get extra results when I search for myself or the boy I share a name with.  For medical claims, the genius programmers set things up to search by name and ignore date of birth (even though both are displayed as the result of the search).

So, yeah, now I can believe an insurance company wouldn't comprehend twins.

Monday, January 17, 2011

Book Review: Raising Twins

Raising Twins: What Parents Want to Know (And What Twins Want to Tell Them)

I haven't done any book reviews for since the twins were born -- mainly because I haven't had a lot of time for reading. I kept thinking about one book that I had read after I had tired of the reviews and decided to go back and look at it again.  Of course, I had read so many books, it was difficult to remember which one it was!

After much searching, I discovered that it was Raising Twins: What Parents Want to Know (And What Twins Want to Tell Them).  Upon re-reading, I see that this book has several things going for it, and one major strike against it.

  • The "What Twins Want to Tell Them" subtitle refers to the numerous interviews with twins sprinkled throughout the book.  I am reminded of a one-credit course I took on the politics of East Asia when I was in college.  The course had a succession of guest speakers, and midway through the class, my classmates pointed out that we finally got one who was Asian.  In other words, it's all well and good to hear from the "experts", but interviews with actual twins give a much-needed perspective.
  • The book takes a developmental approach.  For various ages, it first explains what a child can normally be expected to do at that particular age, then it revisits the topic to tell you how twins may differ.  It sounds obvious, but I found this approach to be unique among the books I've read, and it was a really good way to understand what to expect.
  • Tied in with the previous point, the book goes into a lot of detail to explain why twins need certain things.  In my review of Double Duty, I questioned the advice not to refer to your kids as "the twins" and suggested it was not that different from referring to any set of siblings as "the kids".  Raising Twins, on the other hand, explained that twins in particular struggle with differentiating themselves from their "co-twin", so it can be particularly important to use their individual names, in a way it might not for singleton siblings.
  • The book addresses twin development all the way through high school, which is somewhat unusual for a book about twins.  Most such books handle the first year, or the first few years, and, I suppose, assume that parents who survive that long can handle things for themselves.  I was interested to read how the twin relationship continues to play a role, even for teenagers.
Alas, the last positive point is also a negative point.  Because the book describes development spanning a period of eighteen years, there is very little about each specific age.  If I wanted to know a lot about six-month-old twins (I do!  I do!), there was just one tidbit, although a very interesting one.  (Children at this age may start to use transitional objects to comfort themselves when separated from their mother.  For a twin, this object may actually be his or her sibling.)  I can't imagine lugging this book around for eighteen years, only to pull it out every six months and remember what advice it has at this point.  For this reason, I cannot give the book my fullest endorsement.

Twinometer: 8/10.

    Sunday, January 16, 2011


    I like to make the point that identical twins are not really "identical" -- hopefully most people realize that every individual has traits that are not determined by genetics.  But did you know that some identical twins have differences that are determined by genetics?

    According to the McGraw Hill Encyclopedia of Science & Technology,
    For example, the random “shutting down” of one X chromosome in every female cell soon after conception (a process called lyonization) can cause monozygotic female twins to differ in X-linked traits, such as color blindness.

    Friday, January 14, 2011

    Missed it by that much...

    At the suggestion of a twin parent quoted in one of the books we read while awaiting the arrival of the twins, we are thinking of not telling the boys which one of them is the first-born twin until they're older.  People tend to attach an almost supernatural importance to birth order, and the difference of a minute doesn't seem that important in the grand scheme of things.

    Some twins, however, don't have that luxury.  Princess Mary of Denmark just gave birth to twins.  Because of a difference of twenty-six minutes, the boy is one rung ahead of the girl in the line of succession to the Danish throne.

    Based on the twenty-six minute difference, I'm guessing Princess Mary didn't have a C-section.  But if she did, that could have changed the birth order.  Hopefully this succession never becomes important (the twins have two older siblings), but if it did, it would be one instance where birth order really did mean something for twins.

    Monday, January 10, 2011

    Twins in Popular Culture: The Social Network

    OK, so I haven't seen The Social Network, but I think that's no reason to avoid commenting on it.  The New York Times recently ran an article about the Winklevoss twins' ongoing lawsuit against Facebook.  What jumped out at me was this sentence:
    They are as physically striking and imposing as they appeared in the film, “The Social Network, where they were portrayed by one actor, Armie Hammer.
    One actor?  Isn't this offensive to twins?  In addition to perpetuating the myth (that this blog fights tirelessly against) that identical twins are the "same person", doesn't it take away jobs from hardworking twins to have Mr. Hammer act in "twinface" in this movie?

    Or am I taking this too far?

    Saturday, January 8, 2011

    Popular Excuses

    (Crossposted from Christina's blog)

    It's hard to be a lone pamphleteer with a house full of babies. Because I spent all of 2010 either pregnant or mothering twins, I have slacked off on my blogging. If ever there was a good excuse for abandoning a fun but fruitless activity like blogging, it's twins.

    Having twins, in fact, are a good excuse for many human failings.

    "Oh, yes, you need to get me into the OR right now. I'm having twins."

    "Excuse me, can I slip by you? I know this stroller's huge but I have twins."

    "Sorry we're so late. Twins!"

    In the future I see them being blamed for lots more failings ("Who has time for makeup with twins?") but I'd like to keep the scapegoating to a minimum. After all, I wouldn't want them to get a complex or something. Twins are complex enough. Though I am likely to continue using my favorite line on parents of singletons:

    "So what do you do with all your free time?"

    Sunday, January 2, 2011

    Four of Me

    I recently saw an ad for an upcoming series on Lifetime, "Four of Me". The announcer informs us that the chance of getting struck by lightning is 1 in 6,000, while the chance of having identical quadruplets is 1 in 100,000,000. Then the words, "Which Would You Choose?" flash on the screen.

    Now, the name of the website is, so I try to keep things triplet- and quad-free around here (mostly).  So let me share my reaction, as a parent of identical twins, to this ad.  First of all, you mean I could have two more like the ones we already have?  Yes, please!  Secondly, wait, they're offering injury and possibly death as an alternative?  Isn't that a bit offensive/drastic?

    The show follows the lives of the 17-year-old Durst quadruplets.  The web is not exactly awash with information on the show, though you can find out that they shot an episode in Las Vegas recently.  If you're looking for earlier video, you're more in luck.  Here you can see them in 1998 on "Maury"Here they are in 2000 and again in 2007 on the "Today Show"Here's a "Tonight Show" clip from around 1999.  Hopefully they've developed more interesting schtick than all talking at the same time.

    Of course, I'm going to watch the show, but I don't have high hopes.  Reality TV isn't known for bringing out the best in its subjects, and the show's title speaks to a common problem of taking "identical" too literally.  But, c'mon, identical quadruplets -- who doesn't want to see how that turns out?