Good thing that it's possible for a couple to take a test that gives a good measure of their degree of consanguinity.

This is a particular risk not only in countries with first-cousin marriage, but in those with small founder populations. For example, Iceland, where the government provides this measure to any couple who asks, so that they can make an informed decision about the risk before reproducing.

And ethno-nationalists can choke on this fact: the best strategy to reduce the risk of genetic defects is out-marriage. The less closely genetically similar two partners are, the lower the odds of autosomal recessive disorders afflicting their offspring. So I did the rational thing, and married someone whose ancestors came from a different part of the world than mine.