If you suffer from endometriosis you may have pondered on how you came to have the disease. Did you inherit it from a family member? Did the disease arise from something you were exposed to whilst you were still in the womb? Or did exposure to something factors during childhood or adulthood bring on the disease? It’s not just sufferers that are puzzled by this question, scientists also wonder how and why some women get endometriosis and have had a fair go at trying to answer it.
You may have heard about some of the theories going around. Retrograde menstruation is the go-to theory for explaining how endometriosis comes to be. This basically states that during a period although most of the blood exits via the vagina, some of the blood travels upward into the fallopian tubes and out into area surrounding your various reproductive organs. This blood contains endometrial tissue (that normally lines the womb) which is thought to implant on the organs it settles on and grow to become endometriosis. There’s a neat little animation explaining how retrograde menstruation works on the Endometriosis Research Foundation website and can be found here.
The problem with this theory is that it has been found that 90% of women experience retrograde menstruation, so how come only 10% of women get endometriosis? The retrograde menstruation theory also assumes that menstruation is nessacary for endometriosis to develop. Well an interesting study has just been published in the journal of Experimental and Clinical Cancer Research which has presented some new evidence suggesting women are born with endometriosis.
This study took on the task of dissecting 36 human female foetuses, which had either been aborted or died of natural causes, and looked for evidence of displaced endometrial tissue, the hallmark of endometriosis. What they found was that out of the 36 foetuses, 4 showed evidence of endometriosis. This was remarkable for two reasons, one for the fact that endometriosis had apparently been found in developing foetuses, suggesting that women are in fact born with endometriosis, and two because 4 out of 36 individuals with endometriosis is roughly what you would expect to find in an adult female population.
As interesting as this is, the question remains, how does this displaced endometrial tissue get there? Retrograde menstruation clearly cannot be the answer. The authors of this research suggested that there is an error during the foetal development of the reproductive organs. You see when the foetus is in its very early stages of development it is neither male nor female, it has two sets of ducts, the Wolffian duct (which goes on to become the male reproductive organs) and the Müllerian duct (which goes on to become the female reproductive organs). There is a nice diagram of the various ducts and how they develop here.
The body sends signals to these ducts telling them to become the correct part. So if you were a female the Wolffian duct would disappear and your body would send signals to different parts of the Müllerian duct saying “ok this bit becomes an ovary, this bit becomes a uterus, this bit is the endometrium, this bit becomes a vagina etc etc”. The trouble comes when these signals get muddled (possibly environmental toxicants are messing up the signal, or the messages your DNA is sending are wrong) you get the wrong bits growing in the wrong place. This is basically what these researchers are suggesting, that during the body’s early development, the signals are getting mixed for whatever reason and bits of endometrium end up developing where they shouldn’t (this is called ‘Müllerianosis’), then when puberty hits these bits of displaced endometrium that have been lying dormant since birth become active, and the result is endometriosis.
Overall it’s an interesting new theory on the origin of endometriosis to consider however, there will need to be much more investigation along this line before it is widely accepted, but provides the background work for future research. Additionally if this theory becomes accepted then the next question to ask will be “So what’s messing up the signals?” You can read the article in its entirety by following the links on this page.