The Donner Party certainly was no joke, but there were many Patrick Breens in the United States, and only one of them was in the Donner Party. I suppose that most of the Patrick Breens in America and Ireland were related, closely or distantly. So far as I can tell--but I do make many errors, my in-law Breens descended from a man named Patrick Breen and my in-laws knew about the Patrick Breen in the Donner Party and thus made a connection, thinking that Patrick Breen was a unique name.
The Patrick H. Breen that I record was born March 03, 1843, in Ballingford in County Kerry, Ireland. He died on June 13, 1907, and was buried in St. Ann's Cemetery in Vail, Iowa. I have no record of his immigration route, but some of his in-laws and kin came through Canada. His parents were probably Henry "Harry" Breen and Margaret "Peggy" Mulvihill--so far as I know.
If you know more about these people, I would appreciate input. I keep track of these lines so that my children will know all sides of their ancestry.