title: H-Y antigen and homosexuality in men.
abstract: In men, sexual orientation correlates with the number of older brothers, each additional older brother increasing the odds of homosexuality by approximately 33%. It is hypothesized that this fraternal birth order effect reflects the progressive immunization of some mothers to Y-linked minor histocompatibility antigens (H-Y antigen) by each succeeding male fetus, and the concomitantly increasing effects of H-Y antibodies on the sexual differentiation of the brain in each succeeding male fetus. This hypothesis is consistent with a variety of evidence, including the apparent irrelevance of older sisters to the sexual orientation of later-born males, the probable involvement of H-Y antigen in the development of sex-typical traits, and the detrimental effects of immunization of female mice to H-Y antigen on the reproductive performance of subsequent male offspring.
authors.affiliation: Department of Psychiatry, University of Toronto, Ontario, Canada. blanchardr@cs.clarke-inst.on.ca
authors.forename: R
authors.initials: R
authors.lastname: Blanchard
authors.forename: P
authors.initials: P
authors.lastname: Klassen
mesh_terms: D000818:Animals; D001722:Birth Order; D006182:H-Y Antigen; D018451:Homosexuality, Male / Q000706:statistics & numerical data*; D006801:Humans; D007114:Immunization; D008297:Male; D051379:Mice; D012744:Sex Ratio
chemical_list: D006182:H-Y Antigen