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Birth defect risks same for cousins as mothers over 40 - study

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  • Chris King
    Below is an article stating that birth defect risks for cousins are 2% higher than the general population and claiming that legislation against first cousin
    Message 1 of 1 , Dec 24 2:15 AM
      Below is an article stating that birth defect risks for cousins are 2% higher than the general population and claiming that legislation against first cousin marriages e.g. in some US states is outmoded.  This study doesn't seem to consider the cumulative incidence of recessive disorders when cousin marriage is common.

      This is in start contrast to data from a BBC investigation into endemic cousin marriages to retain wealth in the family occurring in rural Pakistani immigrants to the UK posted to SP on 11 Feb 2008 which showed "British Pakistanis accounted for 3.4% of all births but have 30% of all British children with recessive disorders". 


      This is 400% over normal abnormailty rates not 4%.

      Birth defect risks same for cousins as mothers over 40 - study
      11:38AM Wednesday Dec 24, 2008

      Cousins have no more risk of producing a child with birth defects than women over the age of 40, according to latest research.

      Otago University professor of molecular ecology and evolution, Hamish Spencer, and US researchers led by Diane Paul, of Harvard University, said laws in some parts of the world banning marriage between first cousins are based on outdated assumptions of the degree of genetic risk.

      While marriage between cousins is legal in New Zealand and Britain, but not generally recommended, such a union is banned or restricted in 31 states in America.

      Some states permit the union if the couple have genetic counselling, if one partner is too old to produce children or is sterile.

      The average risk of birth defects in children born to cousins is estimated at 1.7 per cent to 2 per cent higher than the risk to the general population. The risk of the baby dying in childhood is estimated to be 4.4 per cent higher.

      "Women over the age of 40 have a similar risk of having children with birth defects and no one is suggesting they should be prevented from reproducing," Prof Spencer said.

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      Outdated legislation in some countries reflected prejudices about immigrants and the rural poor, and relied on oversimplified views of heredity, he said.

      "There is no scientific grounding for it."

      Socio-economic and environmental factors were often responsible for clouding the birth defect statistics, the research team found.

      "Inbred populations, including British Pakistanis, are often poor. The mother may be malnourished to begin with, and families may not seek or have access to good pre-natal care."

      This resulted in fewer defects being picked up through pre-natal screening and fewer terminations as a result, skewing the overall statistics.

      Women over the age of 40 were not prevented from childbearing, nor were people who had a hereditary disease, such as Huntington's, which carries a 50 per cent risk of being passed on, researchers said.

      Laws banning cousins from marrying should be repealed because "neither the scientific nor social assumptions that informed them are any longer defensible", they said.

      The research was published in PLoS Biology - a public access, peer-reviewed journal.

      - NZPA
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