If it required charts to explain and took years to work out then I’m guessing it probably wasn’t first cousin’s, and may not have even been second cousins. By the time you are at that level the risk is probably barely different than picking someone from the same country as you at random.
That doesn’t mean fucking someone that close to you doesn’t come with risks.
But as long as it’s not multigenerational it’s a very small increase to the already small percentage of defects.
If it required charts to explain and took years to work out then I’m guessing it probably wasn’t first cousin’s, and may not have even been second cousins. By the time you are at that level the risk is probably barely different than picking someone from the same country as you at random.
Could be a case of a long lost uncle