The bed nucleus of the stria terminalis (BST) is involved in emotional responses and male sexual behaviour in rats.
This area is larger in men than women and is female-sized in transgender females (Kruijver et al. 2000).
People with GD have a BST which is the size of the sex they identify with, not the size of their biological sex.
This fits with people who are transgender who feel, from early childhood, that they were born the wrong sex (Zhou et al. 1995).
ao1: genetic basis- indicated in twin studies
Coolidge et al. (2002) studied 157 twin pairs (MZ and DZ) and suggest that 62% of these cases could be accounted for by genetic variance.
Heylens et al. (2012) found that nine (39%) of their sample of MZ twins were concordant for GD, but none of the DZs were.
ao3: One limitation is that brain sex theory assumptions have been challenged.
Hulshoff Pol et al. (2006) scanned transgender individuals' brains during hormone treatment size of BST changed significantly.
Kruijver et al. and Zhou et al. examined the BST post-mortem and after transgender individuals had received hormones during gender reassignment treatment.
This suggests that differences in the BST may have been an effect of hormone therapy, rather than the cause of gender dysphoria.
ao3: One strength is that there may be other brain differences.
Rametti et al. (2011) analysed brains of both male and female transgender individuals, crucially before they began hormone treatment as part of gender reassignment.
In most cases, the distribution of white matter corresponded more closely to the gender the individuals identified themselves as being rather than their biological sex.
This suggests that there are early differences in the brains of transgender individuals.
