Jim Beaux
11-26-2008, 04:29 PM
TS gene an evolutionary advantage?
Thanks to JattaTS, who raised the AR gene topic a while back. The link I have provided goes into more explanation, necessary for an accurate understanding. I have also just found a second study of AR gene action, much bigger, that comes to a different conclusion.
http://www.alertnet.org/thenews/newsdesk/HKG241361.htm
Scientists working in various institutes in Melbourne, Australia and in California conducted a study of 112 mtf transsexuals and 258 non-TS males. They found that a longer version of the androgen receptor gene (AR gene) occurred more often in the mtf TS group than in the control male group (at a statistically significant level).
In most reports, this is where terminology crept in. The longer version was normally labelled ‘defective’, possibly leading to ‘under masculinisation’ or ‘incomplete masculinisation’ of mtf TS brains.
It’s terminology that looked suspect to me. Even more so when I saw the figures – the longer AR gene was found in 55.4% of the mtf TS, and in 47.6% of the control males.
Intelligent commentators have noted that this cannot be the only cause of mtf transsexualism. It is missing in too many mtf TS and present in too many non-TS men.
http://www.medicalnewstoday.com/articles/130421.php
This European study of AR gene action has just been published. It studied AR gene action in 2,878 men, aged 40 to 79) in 8 countries across Europe. The report is quite tough to digest, but here are the key findings.
The longer AR gene was found to coincide with higher levels of testosterone. And various medical checks related to the impact of testosterone showed these to be normal i.e. it seems the fact that the AR gene does not react as much to testosterone is balanced out by more testosterone.
However, the longer AR gene also coincided to higher levels of estrogen. There are various ways in which testosterone is used in the body resulting in estrogen. The researchers are saying this is the effect that is important, because medical checks that correlate with excess estrogen also match up with the longer AR gene.
The bottom line is that the impact of having a longer AR gene is not under-masculinisation, but above average levels of estrogen in males.
Note this finding is not restricted to mtf TS. It simply applies to those with the longer AR gene.
Those with the longer AR gene tend to have poorer sperm production and/or transsexualism. Note ‘tend to’.
Those with the shorter AR gene tend towards prostate cancer, adverse plasma lipid profiles and male alopecia.
NB The report notes there is no difference in sexual function (crudely, ability to perform) between the groups.
Finally, personal comments. Remember that the European study, although much larger, was carried out on 40-79 year olds (and hormone production varies with age).
For the moment I can only see this as simple evolutionary variation. The short AR gene gets a lead in fertilisation, but lags behind in blood work, baldness, and a fairly common cause of death in males.
Thanks to JattaTS, who raised the AR gene topic a while back. The link I have provided goes into more explanation, necessary for an accurate understanding. I have also just found a second study of AR gene action, much bigger, that comes to a different conclusion.
http://www.alertnet.org/thenews/newsdesk/HKG241361.htm
Scientists working in various institutes in Melbourne, Australia and in California conducted a study of 112 mtf transsexuals and 258 non-TS males. They found that a longer version of the androgen receptor gene (AR gene) occurred more often in the mtf TS group than in the control male group (at a statistically significant level).
In most reports, this is where terminology crept in. The longer version was normally labelled ‘defective’, possibly leading to ‘under masculinisation’ or ‘incomplete masculinisation’ of mtf TS brains.
It’s terminology that looked suspect to me. Even more so when I saw the figures – the longer AR gene was found in 55.4% of the mtf TS, and in 47.6% of the control males.
Intelligent commentators have noted that this cannot be the only cause of mtf transsexualism. It is missing in too many mtf TS and present in too many non-TS men.
http://www.medicalnewstoday.com/articles/130421.php
This European study of AR gene action has just been published. It studied AR gene action in 2,878 men, aged 40 to 79) in 8 countries across Europe. The report is quite tough to digest, but here are the key findings.
The longer AR gene was found to coincide with higher levels of testosterone. And various medical checks related to the impact of testosterone showed these to be normal i.e. it seems the fact that the AR gene does not react as much to testosterone is balanced out by more testosterone.
However, the longer AR gene also coincided to higher levels of estrogen. There are various ways in which testosterone is used in the body resulting in estrogen. The researchers are saying this is the effect that is important, because medical checks that correlate with excess estrogen also match up with the longer AR gene.
The bottom line is that the impact of having a longer AR gene is not under-masculinisation, but above average levels of estrogen in males.
Note this finding is not restricted to mtf TS. It simply applies to those with the longer AR gene.
Those with the longer AR gene tend to have poorer sperm production and/or transsexualism. Note ‘tend to’.
Those with the shorter AR gene tend towards prostate cancer, adverse plasma lipid profiles and male alopecia.
NB The report notes there is no difference in sexual function (crudely, ability to perform) between the groups.
Finally, personal comments. Remember that the European study, although much larger, was carried out on 40-79 year olds (and hormone production varies with age).
For the moment I can only see this as simple evolutionary variation. The short AR gene gets a lead in fertilisation, but lags behind in blood work, baldness, and a fairly common cause of death in males.