Homosexuality, type 1: an Xq28 phenomenon.

Despite the absence of phenotypic manifestations in alternating generations characteristic of X-linked disorders, a thesis is presented that a major type of Kinsey grades 5 and 6 male homosexuality is determined by a gene in the Xq28 region. A total of 133 families in 78 kinshps of male and female homosexual probands, in addition to 116 families (including those of 40 famous homosexuals) from the literature, revealed an unbalanced secondary sex ratio in the maternal generation of male, but not of female, homosexuals. On the maternal side, in this study, the ratio of all uncles to all aunts of 90 males homosexuals was 132/209, chi 2 = 8.52, p = 0.004. On the maternal side for the total of all sources, the ratio of uncles to aunts of male homosexuals was 241/367, chi 2 = 13.20; p < 0.0001. The male/female ratio of the total number of maternal sibships bearing homosexuals (310/628: 0.491) was a measure of fetal wastage of the mothers' male sibs; 49%. This ratio was very close to that of the total number of children born to fathers affected with any one of nine Xq28-linked male semilethal conditions (255/508: ratio 0.556); for the difference between the two populations chi 2 = 0.859, p = 0.354. The male/female ratio of the total number of children born to female carriers of any one of these same conditions (1,232/1,062: ratio 1.16), chi 2 = 13.8 p < or = 0.0001, is close to that of the total number of children in homosexual sibships: 511/413, chi 2 = 10.4, p = 0.005. Between the number of children born to Xq28 mothers and to those born of mothers of homosexuals chi 2 = 0.581, p = 0.446. One may readily surmise that the maternal influence so often related to homosexuality may lie in the mother being a genetic carrier, with traits thereto associated. In this study, 65% of the mothers of homosexuals had no or only one live-born brother. Additional support for a genetic hypothesis is found in the occurrence of multiple instances--almost exclusively among maternal relatives--of infertility, spontaneous abortions, miscarriages, stillbirths, remaining single past age 30, and suicide. Of 109 male and 43 female homosexual index cases in the present series there were 6 instances of brother/sister homosexual sibships.(ABSTRACT TRUNCATED AT 400 WORDS)