Discussion:
We introduced a monozygot (MZ) female twins with normal physical, mental, hormonal evaluations which were concordant for GD. Within different severity of GD in each pairs, paradoxical temperaments features were also detected between them.
It is speculated that the development of gender in accordance with its anatomical sex in childhood could be directed by children’s temperament and their dynamic relationship with parents(4). However, the etiology of GD encompasses complicated biopsychosocial factors; including congenital adrenal hyperplasia or androgen insensitivity syndrome, utero exposure to phthalates in plastics and polychlorinated biphenyls, maternal toxoplasma infection, and in individuals with psychiatric illnesses or with childhood abuse, neglect, maltreatment, and physical or sexual abuse is more prevalent. Neuroanatomical links mostly regarding defects in embryonic development and differentiation in hypothalamic networks and variations in amygdala connectivity and hemispheric ratios according to gender have been also found to be associated with GD. Higher prevalence of GD in monozygotic twins than dizygotic twins has been an indicator of heritability and familiarity of GD in genetic studies. Some alleles (CYP17 and CYP17 T-34C) have also been found to have an association (not causation)(5)(6).
According to multifactorial etiology of GD, alongside genetics other factors may play role in navigating the gender identity. As a result, GD in many children do not continue into adolescence and adulthood(7). In this case, we need to follow the twins to check if this concordance for GD is going to be consisted and persisted. Then we will be able to better compare their shared temperament characteristics with GD. There is not sufficient papers to evaluate GD by genetics and twin studies and thereby it is not clear the exact contribution of genetics, familial rearing and environmental factors in the formation of GD. Some other questions also raises like; is it possible that the idea of having SRS shaped as a shared belief between them? Could it be a form of sympathetic reaction that the other pair used to cope situation? How does their concurrent decision for SRS influence the situation? Is it going to be more deteriorating or more acceptable for the parents to get on with? Is this concordance facilitate the pain they have for their gender identity?
Conclusion: In this study we presented twins having concordance GD. It could emphasize the genetic role in GD inheritance but when it came to their different temperaments we assumed this disorder need to be followed up. On the other hand, concordancy in monozygotc twins is still questionable for temperament and gender dysphoria. More twin studies in the future with follow-up will enable us to answer these questions