They may be referring to the 5T, 7T or 9T polymorphism's that people have on the gene that can cause cf. From what I understand everyone has either a 5T, 7T or 9T and the 7T is the normal one to have and does not cause disease. The 5T or 9T can act like a mutation if there are enough of them. Steve from Ambry answred a thread about them a few months ago and I will attempt to post a link to it http://forums.cysticfibrosis.com/messageview.cfm?catid=6&threadid=30665&highlight_key=y.Ok, so my great computer skills aren't working - you can find it by either cutting and pasting that link or by doing a search for a thread that was posted by AbbysMama and it is the first one that comes up - called Needs Some Tutoring - it discussed 5T vs 7T etc.