Objective: A case report is presented of a gender identity disorder involvi
ng a pair of female monozygotic twins who requested sex reassignment. As fa
r as we know, this case is the first in psychiatric literature and supports
a genetic aetiology of this disorder.
Clinical picture: The patients were two 18-year-old female monozygotic twin
s who had showed symptoms of transsexualism since early childhood. They had
no other physical or psychiatric disorder except borderline mental functio
ning.
Treatment: The patients were referred for sex reassignment.
Outcome: They were lost to follow up after initial evaluation.
Conclusion: In addition to other possible (yet not confirmed) causes of tra
nssexualism, a genetic basis for this disorder is suggested by this case.