http://news.bbc.co.uk/2/hi/health/7404730.stm
Professor Alan Bittles, director for the centre for human genetics in Perth, Australia has collated data on infant mortality in children born within first-cousin marriages from around the world and found that the extra increased risk of death is 1.2%.
In terms of birth defects, he says, the risks rise from about 2% in the general population to 4% when the parents are closely related.
However, cousin marriages might typically be in cultures which accept or promote cousin marriages. This might not work out the same way for pairings from non-cousin marriage cultures.
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