My SO's parents are cousins...

[Marumi]

I just learned about that and now I wonder if it could have any ill effect on his offspring?

 

[mamawolf]

I doubt it. Even if they were first cousins. Though the odds of a defect IS doubled with first cousins, that’s still only something like 7%. It’s mostly social taboo (even though it does double the defect rate it’s still low). Besides that wouldn’t affect your child if your SO doesn’t have any genetic defect. Here’s an article about it:

Few Risks Seen To the Children Of 1st Cousins

And for the record, I looked this stuff up after taking one of those DNA tests and finding out that my husband is distantly related to me. Like ~4th or 5th cousins.. eek!