Without reading the entire article, I am not sure I agree with the
conclusion that Jews have less genetic disease than Arabs
because of fewer cousin marriages. (I also think it is odd to
reach this conclusion based upon one type of symptom, which could
have a number of causes).
In the "old country" marriages among Jews were frequently
arranged amongst first cousins or uncles and nieces. This is
one of the reasons Jewish genetic diseases moved rapidly
through the Jewish population. This practice ended because
of the transfer of population to the US, Western
Europe and Israel. With accompanying secularization and a
less insulated society, people could meet and marry anyone
they chose, and it was less likely to be a close relative.