Perfect Pitch Puzzle

Charlotte Harris, only female member of Lawrence Welk's TV orchestra, was interviewed at the close of last night's old Welk show on PBS TV. She said her entire family of six all had perfect pitch. I think she referred to herself, three siblings and both parents. How rare is that? Has it happened before? Has anyone done a family study about it? There is a fellow who advertises in the musician's magazine and on the net, claiming he can teach us to develop perfect pitch. Most scientists who are into psycho acoustics say you're either born with it or you're not. Does anybody really understand the phenomenon?