It is absolutely genetic, and seemingly more prominent in Angus than other breeds but we also see it in Herefords. I personally have not heard a lot about it Shorthorn mainly due to the lack of them being used here in my area. I have heard of some of the continental breed having some problems but again the commercial guys don't use a lot of them in the extrem high elevations. Pneumonia will bring it out in cattle very quickly and anyone purchasing cattle from lower elevations should visit with the breeder to see if the cattle were ever sick with any bronchial infection. I sale bulls to several commercial ranches that run their cows as high as 13,000 feet during the summer and they will not even look at cattle unless they have a PAP test (pulmonary arterial pressure). I know of several ranchers have a contract written when the go to purchase bulls that they present to breeders to look at and sign before they will purchase animals form them. I have been lucky enough to have very little trouble with it in my herd and when an animal shows up with it they go down the road.
Now as for the girl in Wyoming, what the poster describes does not sound exactly right for Big Brisket, most of the time the disease will take several days, weeks or as long as a month or two to develop and terminate the animal. To my knowledge and experience I have never seen one die over night from big brisket.
So I would suggest that anyone purchasing an animal from lower elevations to visit in depth with the breeder about the health of the prospect from birth, of course no one can know the genetic make up of some of these animals in regards to the likelyhood of the disease. I do know that both ABS and Select Sires have information as to bulls status for big brisket, I have not asked some of the other semen distributors if they provide information but as much of a potential problem as it can be I am sure that they do. They recommend for the PAP test to be accurate the animal needs to be tested at an elevation over 6000 feet. You can get more information about big brisket at Dr. Tim Holt's web site and I am sure Tim would be happy to visit with anyone about the issue if they would like to call him.
I would recommend that the girl in Wyoming call the people that she purchased her steers from and talk to them about the issue, for the money that she spent I would think they would want to help in some way if they can, but at least they will know next time they get a call from Wyoming and make the potential buyer aware that their cattle have had problems in the past.