Many mutants died instantly if their powers were active (e.g., flying or living in extreme environments).
The U.S. government initiated , using piloted Sentinels to "protect" and effectively house-arrest the remaining mutants at the Xavier Institute. Son of M (2006) Series Summary Decimation - X-Men - Son Of M (2006) (Digital) ...
: The X-Gene was completely erased from depowered mutants, making them biologically human. Immediate Fallout : Many mutants died instantly if their powers were active (e