From Endometriosis Update blog (lots of good info- check it out!!):
"Several studies have focused on characterising the endometrium of women with and without endometriosis and found that; yes the endometrium in women with endometriosis is indeed different. The endometrium from women with endometriosis appears to have a higher ability to survive, proliferate and invade, seemingly filling in the missing part of the retrograde menstruation theory.
But, like all great mystery stories, the case is never wrapped up in a neat little package so early on. In recent years more and more evidence is coming to the fore, challenging the theory of retrograde menstruation. In particular there is now quite a significant amount of evidence to show the displaced endometrium that defines endometriosis is, in fact, present before you were even born. There are also rare documented cases of endometriosis in men, women who cannot menstruate and non-menstruating primates; so clearly there is the need for some radical re-thinking.
Maybe we’ve had the whole thing upside-down; maybe it is not the endometrium that dictates the fate of endometriosis, but endometriosis that dictates the fate of the endometrium. A collaborative research effort has provided some evidence to this very end (you can read the full article here). The authors of this study experimentally induced endometriosis in baboons by injecting endometrial cells into the pelvic cavity and letting them form endometriotic implants. They then compared the expression of genes within the endometrium of the baboons with experimentally induced endometriosis and disease free baboons over the course of 16 months. What they found was that the presence of endometriosis (even in its very early stages) led to marked changes (a total of 4,331 genes were altered) in the normal endometrium.
This potentially turns accepted wisdom on its head, in that women with endometriosis are not born with a defective endometrium that gives rise to endometriosis via retrograde menstruation. Rather, if we are to take all the above evidence into account, it appears endometriosis is a condition you are born with that, when the endometriotic implants ‘mature’ lead to changes in the function of the normal endometrium, thus perhaps also accounting for the fertility issues women with endo suffer from." http://www.endo-update.blogspot.co.uk/.../turning-on-its...