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Thread: Use of twins to study complex diseases

  1. #1
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    Use of twins to study complex diseases

    And excerpt from this article...(emphasis added)

    http://www.biostat.sdu.dk/courses/f1...g/hall2003.pdf

    Use of twins to study complex disease

    Comparisons of monozygotic and dizygotic twins are
    frequently used to estimate the environmental and
    heritable factors that contribute to complex diseases. This
    comparison assumes that twin pregnancies, births, and
    early childhood are representative of singleton pregnancies,
    births, and early childhood. Growth of twins in utero is not
    typical of singletons. The effect of intrauterine growth on
    later adult diseases could also be atypical. All twins can be
    expected to have many kinds of in-utero differences, such
    as placental flow in monozygotic twins and the amount of
    microchimerism in dizygotic twins.

    Findings of twin studies need to be viewed with some
    reservation. Twins may not be representative of singletons
    in relation to some complex diseases.
    Furthermore,
    increasing use of artificial reproductive technologies,
    presence of high concentrations of gonadotropins,
    intentionally broken or abnormal zona pellucidas, and
    physiological abnormalities related to culture media might
    have effects on childhood or adult disorders not yet
    recognised or not even present in spontaneous twinning.
    Long-term studies and outcomes must record whether
    twinning was spontaneous, the type of artificial
    reproductive technology used, complications of twin
    pregnancies, placental flow, changes in maternal
    physiology, type of chorion, and microchimerism during
    pregnancy to establish whether twin pregnancies can be
    representative of singleton pregnancies.

    The in-utero adjusted growth rate of both monozygotic
    and dizygotic twins could also alter other pathways that
    protect against certain diseases and predispose to others.
    Differences in maternal metabolism during twin
    pregnancies versus singleton pregnancies—with lower
    packed-cell volumes, more gestational diabetes, greater
    cardiac output, etc—could also alter the metabolism of
    the embryo and fetus.

    These observations have interesting ramifications for
    the Barker hypothesis,93 which suggests that diminished
    intrauterine growth predisposes to early onset of
    hypertension, cardiovascular disease, and diabetes in later
    life.However, the smaller twin at birth in a twin pair does
    not seem to have the same type of risk for these diseases as
    is seen in singletons.94–96 An increase in breast cancer97,98
    and testicular cancer94,99,100 has been noted in twins.
    Further, risk of autism has been reported to be increased
    in both monozygotic and dizygotic twins.101,102
    So it seems possible all these twins studies are not going to helpful in the case of complex disease.
    Sharon, mother of identical twin girls with scoliosis

    No island of sanity.

    Question: What do you call alternative medicine that works?
    Answer: Medicine


    "We are all African."

  2. #2
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    Non-identical Monozygotic twins

    http://8e.devbio.com/article.php?id=111

    Most monozygotic twins are remarkably similar. However, there are some equally remarkable exceptions that show that monozygotic twins do not have to be "identical."

    It is usually assumed that monozygotic twins always share the same genome and that their hereditary endowments are the same. Indeed, twins have long been used in studies that attempt to separate "nature" from "nurture". Galton (1875) proposed that the comparison of monozygotic twins to dizygotic twins would show which characteristics are genetic ("nature") and which are conditioned by the environment ("nurture"). However, recent data have suggested that each of a pair of one-egg twins can develop very differently from the other, and these findings of "discordant monozygotic twins" have raised concerns about the assumptions underlying those studies that presume each of a pair of identical twins will develop the same way. In fact, Hall (1996) hypothesizes that the mechanism underlying the separation of blastomeres (which leads to identical twinning) may be genetic changes that distinguish the cells from each other. In this scenario, "identical" twinning is caused by the non-identity of the early blastomeres.

    There are several cases in which identical twins can have discordant phenotypes. The major routes involve aneuploidy, X-chromosome inactivation differences, imprinting, and circulatory differences.
    Sharon, mother of identical twin girls with scoliosis

    No island of sanity.

    Question: What do you call alternative medicine that works?
    Answer: Medicine


    "We are all African."

  3. #3
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    Good find! This is what I was trying to say in many other threads, but put more succinctly! I don't think it dicredits all of the studies, however, because their DNA is most similar to any other's on the planet.

  4. #4
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    this needs re-posting
    Sharon, mother of identical twin girls with scoliosis

    No island of sanity.

    Question: What do you call alternative medicine that works?
    Answer: Medicine


    "We are all African."

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