title: The heritability of gender identity disorder in a child and adolescent twin sample.
abstract: The heritability and prevalence of the gender identity disorder (GID) was examined, as well as its comorbidity with separation anxiety and depression, in a nonretrospective study of child and adolescent twins. The parents of 314 twins (ages 4-17 years; 96 monozygotic pairs [MZ] and 61 dizygotic [DZ] pairs) completed the Coolidge Personality and Neuropsychological Inventory (CPNI) containing a six-item DSM-IV-based GID scale. Prevalence of clinically significant GID symptomatology in the twin sample was estimated to be 2.3%. Univariate model fitting analyses were conducted using an ordinal transformation of the GID scale. The model that best described the data included a significant additive genetic component accounting for 62% of the variance and a nonshared environmental component accounting for the remaining 38% of the variance. Results suggested no heterogeneity in the parameter estimates resulting from age. The correlation between GID and depression was modest, but significant (r = .20; P < .05), whereas the correlation between GID and separation anxiety was nonsignificant (P > .05). Overall, the results support the hypothesis that there is a strong heritable component to GID. The findings may also imply that gender identity may be much less a matter of choice and much more a matter of biology.
authors.affiliation: Psychology Department, University of Colorado at Colorado Springs, 80933-7150, USA. fcoolidg@uccs.edu
authors.forename: Frederick L
authors.initials: FL
authors.lastname: Coolidge
authors.forename: Linda L
authors.initials: LL
authors.lastname: Thede
authors.forename: Susan E
authors.initials: SE
authors.lastname: Young
mesh_terms: D000293:Adolescent; D001010:Anxiety, Separation / Q000235:genetics; D002648:Child; D002675:Child, Preschool; D015897:Comorbidity; D003863:Depression / Q000235:genetics; D004200:Diseases in Twins; D005260:Female; D005783:Gender Identity; D020022:Genetic Predisposition to Disease / Q000235:genetics; D018452:Homosexuality, Female / Q000235:genetics*; D018451:Homosexuality, Male / Q000235:genetics*; D006801:Humans; D008297:Male; D008957:Models, Genetic; D010552:Personality Assessment; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic