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Identical Twins Not Identical After All

Posted by samzenpus on from the one-of-these-things-is-not-like-the-other dept.

Hugh Pickens writes "Contrary to previous beliefs, identical twins are not genetically identical. Researchers studied 19 pairs of monozygotic, or identical, twins and found differences in copy number variation in DNA which occurs when a set of coding letters in DNA are missing, or when extra copies of segments of DNA are produced. In most cases, variation in the number of copies likely has no impact on health or development but in others, it may be one factor in the likelihood of developing a disease (pdf). "Those differences may point the way to better understanding of genetic diseases when we study so-called discordant monozygotic twins....a pair of twins where one twin has a disorder and the other does not," says Carl Bruder, Ph.D. "If twin A develops Parkinson's and twin B does not, the region of their genome where they show differences is a target for further investigation to discover the basic genetic underpinnings of the disease.""

35 of 159 comments (clear)

  1. Identical twins are like Slashdot dupes by Daimanta · · Score: 4, Funny

    You think they are exactly the same, but they are always slighly different.

    --
    Knowledge is power. Knowledge shared is power lost.
    1. Re:Identical twins are like Slashdot dupes by s74ng3r · · Score: 4, Funny

      You think they are exactly the same, but they are always slightly different.

    2. Re:Identical twins are like Slashdot dupes by Anonymous Coward · · Score: 3, Funny

      You think they are exactly the same, but they are always slightly diffenert.

    3. Re:Identical twins are like Slashdot dupes by Thanshin · · Score: 3, Funny

      You think they are exactly the same, but they are always slightly diffenert. The reader concludes the similarities between both are absolute; however, by a negligible disparity, that is not so.
    4. Re:Identical twins are like Slashdot dupes by somersault · · Score: 4, Funny

      You think they are exactly the same, but they are always slyly different.

      --
      which is totally what she said
    5. Re:Identical twins are like Slashdot dupes by Zencyde · · Score: 3, Funny

      Yeah? Well, I read Slashdot for the articles.

      --
      What day is it? Could you please tell me?
  2. Hell that makes it worse by MosesJones · · Score: 4, Funny

    I'm sure we've all had that embarrassing occasion of going out with one twin, getting drunk and waking up with the other. It used to be okay to claim you were drunk and couldn't tell them apart, you'd still get a slap but not a knee in the groin... now they can be told apart using simple genetic testing there really is no excuse.

    In other news the part of the movie industry targeted with making crap movies aimed at teenage boys was shut down as plot lines had become "medically unsupportable".

    --
    An Eye for an Eye will make the whole world blind - Gandhi
    1. Re:Hell that makes it worse by RuBLed · · Score: 5, Funny

      I'm sure we've all had...


      Dude, you're still drunk... this is /. by the way.
      Look behind you, that's your bed... and there are no twins...
    2. Re:Hell that makes it worse by cp.tar · · Score: 5, Funny

      Clearly this wholly explains all those evil twin plot lines.

      Yeah, I've always wondered why it is that the evil twin has a pointy beard.

      I'd never have thought that the cause was genetic.

      --
      Ignore this signature. By order.
  3. So.... by Anonymous Coward · · Score: 3, Funny

    What gene difference made those twins so different (Danny de Vito and Arnold Schwarzenegger)

  4. Wonder how this affects... by Anonymous Coward · · Score: 5, Interesting

    ...decades of experiments that assumed twins have identical DNA. One twin may not be such a good control after all...

    1. Re:Wonder how this affects... by mrbluze · · Score: 5, Interesting

      ...decades of experiments that assumed twins have identical DNA. One twin may not be such a good control after all...

      Well experiments can prove an association of two events, or causation of an event on another. Twin studies show associations and the experimenters usually jump to causation in their discussion to make the paper interesting to read. So it doesn't invalidate the experiments but shows that in all of science we can never assume we have excluded all confounding.

      Actually this finding isn't all that surprising. For example, Trisomy-21 (Down's Syndrome) has different severities depending on how far along the line the trisomy developed (how many cells existed when the trait was introduced). It shows that the genetic makeup within an individual is heterogenous, let alone between two 'identical' individuals. The genetic code in your left hand is likely to differ from that in your right hand by a (numerically) small degree.

      However, if the genetic change is an important one, then it follows that your left hand might be very different from your right (eg: more hair on one than the other, or one side more likely to develop cancer, etc).

      --
      Do it yourself, because no one else will do it yourself. [beta blockade 10-17 Feb]
    2. Re:Wonder how this affects... by JeffL · · Score: 5, Insightful

      It doesn't have too much effect, really. MZ twins are similar on a trait because of genes that they share (traditionally, all of them) and environment they share (growing up in the same house, etc.) They are different on a trait due to environmental factors they don't share (such as going to different colleges) and error (measurement error in assessing the trait, random noise, etc.)

      DZ (fraternal) twins are similar on a trait due to the genes they share (on average, 50%, same as any other full siblings) and the environment they share. They are different on a trait due to the genes they don't share (on average 50%), environment they don't share, and error.

      These results say that the assumption that MZ twins share 100% of their genes is wrong. The real question is how wrong? Do MZ twins share 99.99% of their genes? Is that 0.01% difference right in the middle of some gene that has a large effect on the trait you're studying? For most of these new discoveries, it doesn't make any difference at all. Differences in silent mutations between twins isn't going to change scientists' conclusions that height is highly heritable (meaning: most of the difference in height between two people is due to the fact that they have different genes).

    3. Re:Wonder how this affects... by XavidX · · Score: 3, Funny

      you mean eating your veggies does not make you grow big and strong?

    4. Re:Wonder how this affects... by Eivind · · Score: 4, Insightful

      Actually, scientists aren't (universally) that dumb.

      If identical twins are much MORE similar in intelligence compared to non-identical twins, we can conclude that there is a high likelihood that the difference is genetic.

      Identical twins should not normally have more similar nutrition (in pregnancy or thereafter) than nonidentical ones.

    5. Re:Wonder how this affects... by mrami · · Score: 3, Informative

      I'll tell you what I first thought when I read this:

      I read in, I think it was a Steven Pinker book, about studies done on identical twins using the big five personality traits. What he said was that on the big five, identical twins raised together were roughly 50% similar, and identical twins raised apart were... roughly 50% similar. So when it comes to nature/nurture on the big five, you get 50% genetics, maybe 1-2% environment, the rest comes from ?????.

      As you say, those numbers are probably based on the assumption of the genetic code being exactly the same, so those numbers can't represent reality as we know it now. But I'll be interested to see how the numbers fall out after the variance in twins' sequences is factored in. I would guess that it's the explanation for some of the ????? above, but how much?

    6. Re:Wonder how this affects... by skjolber · · Score: 5, Interesting

      As an identical twin myself, I have been included in several national studies. These studies typically address the differences between identical and non-identical twins. It was actually determined through conventional means that it was > 99% certain that we were identical twins, even after living apart for several years. I.e. you would not need DNA testing for determining who's identical i most if not all cases.

      I really do not think this new information will affect previous studies much, because the loss in precition is probably much higher due to non-genetical, i.e. external, factors. However this new insight opens the door for new identical-only studies, where external factors also are kept to a bare minimum.

      I would also like to point out that to a twin, it is clear that identical twins are in fact not equal. I my case we looked very alike untill about 20 years, however now (at 29 years) it is clear to everyone to see that there are clear (visual) differences. This should, in terms, tell all you non-twins that your current physical apperance (++) is actually one within a possible range you could have become, for better or worse.

      --

      Two for the price of one

  5. News Flash! by Strange+Ranger · · Score: 3, Funny

    After the sperm penetrates the ovum, a zygote is formed. After which, chaos ensues.

    Growth and development of one copy != growth and development of the other.

    --

    Operator, give me the number for 911!
    1. Re:News Flash! by repapetilto · · Score: 5, Interesting

      Right, and it seems like their making a false dichotomy between environmental factors and DNA replication "errors," one can lead to the other (well replication errors can lead to susceptibility). Think about your skin cells, people who spend alot of time outside end up with their skin adapted. Its not just upregulation of whatever leads to more pigment, there is actually competition going on amongst the cell lines, those that survive better start to spread. Eventually even the whitest person you know will have permanently darker skin (if it doesn't kill them first that is). Same with every organ I imagine.

    2. Re:News Flash! by Anonymous Coward · · Score: 5, Funny

      well its not chaos...

      You clearly do not have a four-year-old. Now if you'll excuse me, I've got to go vacuum the bookshelf. Don't ask.

  6. Disease gene hunting by reprint · · Score: 3, Insightful

    This is certainly another tool for those hunting genes associated with disease. These are complex diseases however with multiple genetic alterations so the identification of a single gene may not provide the whole story. Also a gene identified this way may not apply to the larger afflicted populaton since this is a correlation seen in a small study group. It should be relatively easy to check though.

  7. Twins aren't Identical? by Anonymous Coward · · Score: 4, Funny

    Well, duh.

  8. Amazing breakthough! by brit74 · · Score: 5, Funny

    I'm sure this will explain why the evil twin is evil. It's an amazing breakthrough in the field of soap opera science!

  9. Re:Err..... by dltaylor · · Score: 3, Informative

    Blindingly obvious? It requires a tremendous ability to detect genetic differences when the difference is a nothing more than the number of copies of a few base pairs in an entire genome (~3,000,000,000 base pairs). We still don't know whether there are any epigenetic differences, or what those might be, because that is even more difficult to measure.

    While it may seem obvious to the uneducated that twins are "different", there is a lot of research that shows high correlation, even when the twins are raised apart, so identifying the cause(s) of the differences and whether those are "nature" or "nurture" is still of value. Even within a family, the differences may be simply something like feeding order, where the earlier fed may get different (not necessarily better or worse) nutrition or bonding experience than the later fed, rather than, necessarily, a genetic difference.

    When it is copy numbers, or very small polymorphisms, and there is some somatic variation, we can use the data to more closely identify which genetic values are associated with the variation.

  10. That was known for quite a while by bogd · · Score: 5, Informative

    I remember that during medical school (maybe 7 or 8 years ago) we were told that while identical twins have extremely similar DNA to each other, that DNA is not 100% identical. Maybe 98 or 99% (more than any other two individuals on this planet), but not 100%. So while this is an interesting research, it hardly qualifies as "news"...

    1. Re:That was known for quite a while by Rhabarber · · Score: 3, Informative

      Hmm, you mean just like my DNA is 99% identical to that of every chimp ;)

      Also remember that many of your cells carry DNA of all those viruses you got exposed to without even noticing. And while we talk about infections, the immune system comes in mind, with all those crazy DNA recombinations taking place during its development. Not to mention spontaneous mutations which are not that insignificant tumorigenesis.

      Nobody actually ever believed that twins are 100% identical. They just want to make up their story. Nothing new to see here ...

    2. Re:That was known for quite a while by Spacezilla · · Score: 4, Funny

      My identical twin IS a chimp, you insensitive clod!

  11. *AHEM* by AlgorithMan · · Score: 5, Funny

    http://xkcd.com/263/
    ;-)

    --
    The MAFIAA is a bunch of mindless jerks who will be the first up against the wall when the revolution comes
  12. Copying introduces errors by tsa · · Score: 3, Insightful

    When 3 billion basepairs are copied when a cell is divided, it seems logical to me that errors occur. So why isn't the fact that 'identical' twins are not truly identical a no-brainer to the experts? I know this remark sounds like a troll, but I'm genuinely surprised.

    --

    -- Cheers!

    1. Re:Copying introduces errors by mrbluze · · Score: 3, Insightful

      Scientific research is only as good as the people conducting it and what motivates them. From what I've seen, only a small number of people are genuinely excited by the stuff they are researching. The rest of them are chasing a PhD or some other claim to fame. But also coming up with a good study and designing it well to make it valid is not easy. It takes creative imagination and intelligence. Whilst there are many people with these qualities, it's frighteningly hard to find them at scientific meetings.

      --
      Do it yourself, because no one else will do it yourself. [beta blockade 10-17 Feb]
  13. This may explain WHY there are "identical" twins by mlwmohawk · · Score: 3, Interesting

    I wonder, maybe the egg always splits when minor genetic errors happen as a method to protect the embryo. The vast majority of the time, the part that splits dies and is reabsorbed. On odd occasions, the genetic mutation is viable and becomes a twin.

    That would imply that the second twin always has some sort of mutation from the first.

  14. I Had Noticed Something by marzipanic · · Score: 4, Interesting

    As a proud mum of identical twin boys I had noticed that mine seem distant as opposed to those who feel empathy for each other.

    They are part of a twin study, which basically involved some of the placenta, blood tests and for a few months DNA swabs from inside the cheek. The study never got back to us with the results yet as I believe it is still ongoing. But yes it was confirmed they are definitely identical.

    As babies I used to "colour code" them so I knew who was who, now they are teenagers, totally different but I put it down to personality and obviously different tastes in dress. Silly me....

    I will be following this with interest though! Esp. as one of my sons has autism and they are saying that could be a genetic thing, well I was told by a specialist if one had autism the other would have too? However my GP said that is crap. I have no idea but they are like chalk and cheese except for their voice.

    --
    In the name of sticking up for someone with autism, f**k you! Prejudiced bastard.... that is unlawful and linuc for dumm
  15. Yeah, DNA is identical, but... by Mandovert · · Score: 4, Funny

    ...do MD5 match?

  16. Re:Mothers by ToxikFetus · · Score: 3, Funny

    Could this be why mothers can tell apart their twin offspring?
    I find that a few well-placed scars do the trick.

    Now excuse me while I meet with Child Services.
  17. Epigenetics by ecbpro · · Score: 3, Interesting

    Epigenetics is an important factor that should not be neglegted!
    Depending on the life-style of each twin (and other factors) twins could be identical genetically but very different epigenetically. That means that even though they have the same set of genes they can be completely differently regulated, thus resulting in different susceptibility to diseases.
    (For those interested: One important epigenetic mark is the methylation of DNA at Cytosines thus resulting in the shut-off of genes.)