The search for the origins of transsexualism continues with a gradually increasing bias towards those that are physiological. Some 20 years ago there was a false prophet in the guise of the HY antigen, the antigenic influence on the Y chromosome believed to be influential in the development of the testes. A series of male transsexuals studied in Germany were found to be lacking this antigen and the tentative conclusion reached was that its absence resulted in a failure to masculinize the brain in the direction of a male identity. (12) However, the author's collaborative effort to replicate that study was not successful as all the male transsexuals we studied in the United States appeared to have normal HY antigen. (1„3)
A more recent finding from The Netherlands implicates the brain region known as the bed nucleus of the stria terminalis. In a series of six male transsexuals studied at postmortem over a 10-year period the size of the nucleus was comparable to that of typical females and not males.(14) The nucleus size is believed to be affected prenatally by sex hormone levels. A criticism of this study is that the long-term oestrogen treatment for these males may have altered the size of the nucleus. In response the researchers argue that males treated with antimale hormone drugs or oestrogen for prostate cancer do not have an alteration in the nucleus size from typical males. Another criticism is that the long time of collection, a 10-year period, before the brains were studied may have resulted in an artefactual shrinkage of the nucleus.
Research with male transsexuals has revealed what might be indirect markers reflecting biological distinctions for male transsexuals. In agreement with other researchers' findings that male homosexuals have a greater likelihood of having older brothers, (15> our homosexually orientated male transsexuals also have more older brothers. A theory behind this finding is that there is a progressive immunization with each pregnancy against the male fetus by the pregnant mother perhaps reflecting antigenicity of the HY antigen. (1,5,>
A higher ratio of aunts to uncles on the mother's side has also been found in our male transsexuals, a finding previously reported for a sample of male homosexuals/16' A theory here is that a semilethal factor has been operant in one generation (uncles) that in the subsequent generation influences brain development resulting in an atypical behavioural pattern (homosexual or transsexual development). (1,7> Another theory invokes genomic imprinting.(16) We also find that both male and female transsexuals are more often non-right-handed. This in the male may reflect central nervous system dysfunction or hormonal differences prenatally and in the female similar central nervous system dysfunction or masculinization. (18> Typically males are more often non-right handed compared with females.
For female transsexuals, a series of reports indicates a higher rate of polycystic ovarian disease. (19) Women with polycystic ovarian disease secrete higher levels of androgen than typical females. However, nearly all patients with polycystic ovarian disease are not transsexual and the majority of female transsexuals do not have polycystic ovarian disease.
Was this article helpful?