Family cooccurrence of "gender dysphoria": ten sibling or parent-child pairs.

Ten (10) sets of siblings or parent-child pairs concordant for gender identity disorder (transsexualism) or gender identity disorder and transvestitism are reported. For concordant gender identity disorder, there is one set of male monozygotic twins; three sets of non-twin brothers; one brother-and-sister pair; one set of sisters; and one father and son. With gender identity disorder and transvestism, there is one transsexual father with a gender dysphoric; transvestic son; one transvestic father with a gender dysphoric, transvestic son; and one transvestic father with a transsexual daughter. The emerging technology of genetic markers makes collation of such families a potentially valuable resource for unraveling the origins of atypical gender identity.