Tay Sachs is highly correlated with certain types of Jewish people. The same group is highly above median iq. I don't think smart East Asians populations have higher rates of Tay Sachs. The Cajun and québécois who also have high rates of Tay Sachs are not statistically smarter than median.

It is probably more generally that closed mating groups are more likely to amplify traits good and bad.

I'd say its other way around. They mate for good traits, but the proximity of their genes leaves them open to vulnerabilities like Tay Sachs. That's my view of it at least.