DNA fiddling has been around for quite some time, and it hapens here pretty regularly, to fix birth defects where they can (my own specific difficulty is on the list too) but also to make people less prone to disease.
One problem that was quite common in the early days was lung disease. There were a lot of airbornes when people first settled on La-A, and there was some discussion as to how that could best be handled. Finally a refugee geneticist from one of the russian factory planets suggested a retrovirus with an agent that strengthens the lung tissue, makes it more resistant to disease, allows it to absorb oxygen more readily, and self-cleans. The little cilia that are normally in the lungs are converted to beats-as-it-sweeps-as-it-cleans dirt removal machines.
So before they got the atmosphere cleaned up, a guy could work out in the dusty plains of La-A and not die. He might have wished he could, because at the end of the day you coughed crap up for five minutes, but your lungs were baby-clean and like new again right afterwards.
Newcomers would get the procedure as they arrived, a blood sample to take the genetic fingerprint and then a spray up your nose, and you were set. In about three days your lungs were changed cell by cell, and you never had to worry about lung disease again.
The downside was you tended to be more careless about the things you did. Fumes that were no longer damaging to your lungs were no less poisonous. So people had to be careful, but eventually, it all got sorted out.
Several generations in they discovered the mutation had taken root and all you had to do was come in body-fluid-level contact with an "infected" person and you got the mutation too. I developed it during treatment when i first arrived. Some say it itches during the change but I was too out of it to remember.
Consequently almost everyone here smokes. The chemicals in cigarette smoke are still there and still as damaging and dangerous but nobody here smokes that much, and the price of smoking is a couple hearty coughs in the morning, and you're fine again. Having come from earth it's a bit odd to see offices with ashtrays on every desk, and the ventilation systems in buildings have to be super effficient to keep all the places from smelling like smoke, but we manage fine.
I smoke about a pack a week. Not a big deal, by any standards, and the tobacco here is good. I also light up a pipe about once a week. And a few times a year, someone brings me a handrolled Cuban cigar.