title: Familiality of gender identity disorder in non-twin siblings.
abstract: Familial studies and reports of co-occurrence of gender identity disorder (GID) within a family may help to clarify the question of whether transsexualism is a familial phenomenon. In a sample of 995 consecutive transsexual probands (677 male-to-female [MF] and 318 female-to-male [FM]), we report 12 pairs of transsexual non-twin siblings (nine pairs of MF siblings, two pairs of MF-FM siblings, and one pair of FM siblings). The present study doubles the number of case reports of co-occurrence of transsexualism in non-twin siblings available in the literature. According to our data, the probability that a sibling of a transsexual will also be transsexual was 4.48 times higher for siblings of MF than for siblings of FM transsexual probands, and 3.88 times higher for the brothers than for the sisters of transsexual probands. Moreover, the prevalence of transsexualism in siblings of transsexuals (1/211 siblings) was much higher than the range expected according to the prevalence data of transsexualism in Spain. The study suggests that siblings of transsexuals may have a higher risk of being transsexual than the general population, and that the risk is higher for brothers than sisters of transsexuals, and for siblings of MF than FM transsexuals. Nevertheless, the risk is low.
authors.affiliation: Unidad de Identidad de Género, Instituto Clínic de Neurociencias, Servicio de Psiquiatría, Hospital Clínic, Universidad de Barcelona, Villarroel 170, 08036, Barcelona, Spain. esgomez@clinic.ub.es
authors.forename: Esther
authors.initials: E
authors.lastname: Gómez-Gil
authors.forename: Isabel
authors.initials: I
authors.lastname: Esteva
authors.forename: M Cruz
authors.initials: MC
authors.lastname: Almaraz
authors.forename: Eduardo
authors.initials: E
authors.lastname: Pasaro
authors.forename: Santiago
authors.initials: S
authors.lastname: Segovia
authors.forename: Antonio
authors.initials: A
authors.lastname: Guillamon
mesh_terms: D000293:Adolescent; D000328:Adult; D005190:Family; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D011336:Probability; D019968:Sexual and Gender Disorders / Q000453:epidemiology / Q000601:surgery; D035781:Siblings; D013030:Spain / Q000453:epidemiology; D014189:Transsexualism / Q000453:epidemiology* / Q000601:surgery; D055815:Young Adult