In my family, I have 2 sets of such examples and both sets have children who have turned out to be perfectly fine. I guess the "genes" trouble really crops up when it's a matter of first cousins marrying first cousins. The Catholic church does not give their blessing to first-cousin marriages anyway. Here's a British woman of Pakistani origins with a look at what happens when first cousins marry first cousins like the accepted norm in muslim families.
....My family is not unique. My family is not unique. In the UK more than 50 per cent of British Pakistanis marry their cousins – in Bradford that figure is 75 per cent – and across the country the practice is on the rise and also common among East African, Middle-Eastern and Bangladeshi communities.
Back when my grandparents were having children, the medical facts were not established. But today in Britain alone there are more than 70 scientific studies on the subject.
We know the children of first cousins are ten times more likely to be born with recessive genetic disorders which can include infant mortality, deafness and blindness.
We know British Pakistanis constitute 1.5 per cent of the population, yet a third of all children born in this country with rare recessive genetic diseases come from this community. ...