The congenital condition was diagnosed when Brittany was a teenager and she always had the best medical care for it, Sharon Murphy said.
"We had it checked out every which way you could imagine," Brittany's husband Simon Monjack told People magazine.
Mom Sharon also insisted that Brittany did not do drugs, rarely drank and was not mentally ill -- all of which had been rumored.
Murphy died in December at age 32. Her official cause of death is still pending.