WHAT IS THE RISK TO CHILDREN OF PARENTS WHO ARE CLOSE
RELATIVES?
The risk that those marrying a relative are more likely to have
offspring with birth defects or a disabling condition is nearly
always exaggerated and perceived as being higher than it actually
is.
All parents who are unrelated carry a risk of between 3 and 4% (3
to 4 out of every 100 births) of having a child with a birth defect
or disability.
Where parents are first cousins and there is no family history of a
specific condition, or where there is no other history of parents
being related in previous generations, the risk is approximately
double that for unrelated parents. So the total risk of having a
child with a genetic condition where parents are first cousins is
around 5-6%. Looked at another way, there is approximately a 95%
chance of having an unaffected baby.
However, in societies with a tradition of first cousin marriage,
and where marriages are usually contracted within the community,
many couples are often more closely related than first cousins and
consequently their risk may be significantly higher.
'WHEN PARENTS ARE RELATIVES - CONSANGUINITY',
http://www.genetics.com.au/factsheet/26.htm
