It’s less about denying coverage and more about accurate risk pooling. If an insurer knows a specific marker leads to a 90% chance of a million-dollar claim, they have to price for that. If they don't, the 'healthy' people in the pool end up subsidizing the high-risk ones until the premium becomes too expensive for everyone and the pool collapses (adverse selection). The real challenge is that regulators often won't let insurers price high enough for those risks, which is why many companies just stop offering LTC (Long-Term Care) altogether.

Not in the US it’s illegal under the Genetic Information Nondiscrimination Act (GINA) of 2008.

YEsh, they'll both raise your rates for not submitting this data and raise your rates for being in the cohert that's susceptible; they'll also raise everyone elses rates for having to recalculate the tables!