Remarkably, this same mutation gives the protein an 80,000-fold higher affinity for carbon monoxide than for oxygen. Carbon monoxide from a cigarette will be selectively taken up by the mutant hemoglobin and prevent it from oxidizing and denaturing. This high affinity for carbon monoxide explained why the father showed no signs of anemia, Olson said.
"He may never be an athlete because his blood can't carry as much oxygen, but smoking has prevented him from being anemic," he said. "And there's a side benefit. People with this trait are more resistant to carbon monoxide poisoning."
Read more at: https://phys.org/news/2017-02-case-scientists-mechanics-rare-hemoglobin.html#jCp