Semi-identical twins 'identified for only the second time'

Semi-identical twins 'identified for only the second time'
    Doctors have documented what they say is only the second known condition in the world for "semi-symmetric" twins.

    The boy and the girl, now four from Brisbane, Australia, are identical on their mother's side.

    But they share only a proportion of the DNA of their father - they place it, genetically, somewhere between the fraternal twins and the like.

    Experts say this phenomenon is very rare - embryos like this often do not survive.
    Professor Nicholas Fisk, who led the team that cared for the mother and twins at Royal Brisbane and the Women's Hospital in 2014, said the discovery was made through a routine pregnancy test.

    This is the first time that pseudo-twins have been identified during pregnancy.

    Doctors said that the mother for the first time was twenty eight years at that time and was conceived naturally.

    The case is reported in the New England Journal of Medicine.

    "The ultrasound of the mother in six weeks showed the presence of one placenta and the placement of amniotic sacs indicating that they expect identical twins," Professor Fisk said.

    "However, ultrasound imaging in the fourteenth week showed that male and female twins, which is not possible for identical twins.
    Similar or identical twins occur when one egg, fertilized by a single sperm, is formed and two babies are made.

    These twins will be of the same sex and share the same genes and physical traits.

    Non-identical twins or bisexuals occur when two separate eggs are fertilized, each with different sperm, and grows in the uterus at the same time.

    These twins can be of the same sex or of a different race and are no more similar than any brother or sister, even though they are born together.

    In this case of semi-symmetric twins, or twins, it is believed that the egg has been simultaneously fertilized by two sperm before it is divided.

    If one egg is fertilized by two sperm, it leads to three sets of chromosomes, instead of the second standard - one from the mother and two from the father.

    According to the researchers, three groups of chromosomes "do not usually correspond to life and embryos do not usually last."

    Twins were not identified.
    Asymmetric twins are more common than identical twins and are more likely to appear in families.

    Older mothers are also more prone to asymmetric twins because they are more likely to secrete more than one egg during ovulation.

    Treatment of infertility - artificial insemination - can increase the chance of twins, where more than one fetus can be placed in the uterus.

    According to the Tamba Federation, about 12,000 twin births occur each year in the United Kingdom.

    'exceptional case'
    The first documented case of identical half-twins was in the United States in 2007.

    Professor Fisk said that the analysis of the twin global databases highlighted how rare sesquizygotic twins occur.

    He and his colleagues examined the genetic data from 968 fraternal twins, as well as a number of large international studies, but found no other case of seismotherapy.

    "We know this is an exceptional case of almost identical twins," said Professor Fisk.

    "While doctors may take this into account in seemingly identical twins, their scarcity means that there is no case for routine genetic testing."
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