Being transgender or transsexual.
Gender dysphoria, & gender identity.

Is it caused by fetal exposure
to abnormal androgen levels?

Sponsored link.

What are the causes of being transgender:

The cause(s) have not been thoroughly researched and are not fully understood.

In experiments on some animal species, when a female fetus is exposed to high androgen levels during certain critical stages of gestation, they will exhibit male-like behavior after birth.

The general consensus is that transsexuality in humans is caused by:

	Something in their DNA when they are conceived conception, and/or
	Some process that affects the fetus during gestation.

Is it caused by pre-natal exposure to androgens?

Researcher G. Dorner in 1980 suggested that transsexuality may be caused by a fetus being exposed to an unusual level of androgens -- sex hormones -- while in the womb. He postulated levels that were:

	Above normal levels in the case of female-to-male (FTM) transsexuals and
	Below normal in the case of the more common male-to-female (MTF) transsexuals. 1

Later, Geschwind and Behan proposed in 1984 that sinistrality (left-handedness) may be caused by the fetus being exposed to excessive levels of testosterone -- a male sex hormone. ₂

If these theories are both true, then one would expect:

	FTM transexuals would have a higher than average frequency of left-handedness.
	MTF transexuals would have a lower than average frequency.

Jacob F. Orlebeke et al. in Amsterdam, the Netherlands, decided to test this combination of theories. They found that the level of left-handedness in both FTM and MTF transexuals was about equal and almost twice that found in the general population. They concluded that either Dorner's theory or Geschwind & Behan's theories were wrong, or that both were incorrect.

Their study involved assessing hand/foot preference in a group of Dutch adults. 93 were MTF and 44 were FTM transsexuals. They recorded the transsexuals' behavior when writing, throwing, cutting with scissors, brushing teeth, drawing, and kicking a ball. They found that:

	19.3% of MTF transsexuals were left handed.
	18.2% of FTM transsexuals were left handed.

An independent large-scale study had earlier determined that:

11.2% of the general population of the Netherlands were left handed.

The Amsterdam study concluded that the frequency of left handedness among both MTF and FTM transsexuals throws doubt on either or both of Dorner's and Geschwind & Behan's theories.

Jacob F. Orlebeke et al. wrote:

"... the present data -- in particular the absence of a sex difference with respect to enhanced prevalence of left-handedness in transsexuals -- are in line with the observation that several other pathologies are associated with increased left-handedness, for example, epilepsy and atopic skin diseases. ₃ Among individuals with these chronic diseases, the prevalence of left-handedness is 2 to 3 times higher than in the population in general and occurs to the same degree or sometimes even more often in women as in men. Of children with extremely low birth weights (less than 1,000 g), about 50% are left-handed (O'Callaghan et al., 1987)."

"The common feature behind all of these pathological conditions could be disturbances in the fetal development of the central nervous system, some of which may be caused by exposure to enhanced testosterone levels, and some of which (low birth weight, for instance) are very likely not caused by exposure to enhanced testosterone levels. The fact that the prevalence of left-handedness is higher in epileptic women than in epileptic men (Van den Brekel, 1986) must also be considered as an indication that pathological left-handedness may involve factors other than the degree of prenatal testosterone exposure alone."

"In conclusion, we can say that the nature of our results -- a similarly elevated prevalence of left-handedness among both FTM and MTF transsexuals -- argues against abnormal prenatal testosterone exposure as a factor in the etiology of left-handedness among transsexuals. In fact, our results are similar to those of McCormick et al. (1990), who observed an elevated prevalence of left-handedness in both female and male homosexuals." ₄

More recently, in 2005, H. Schneider, J. Pickel, and G Stalla published the results of their studies of finger lengths in male-to-female (MTF) transsexuals. They specifically measured the ratio in lengths of the second and fourth fingers. This ratio is generally accepted as a marker of androgen exposure in the womb.They found that MTF transsexuals had a higher digit ratio than control males, comparable to their female control subjects. ₅ They wrote: "Our findings support a biological etiology of male-to-female transsexualism, implicating decreased prenatal androgen exposure in [male-to-female transsexuals]. ... We have found no indication of a role of prenatal hormone exposure in female-to-male transsexualism.

References used:

The following information sources were used to prepare and update the above essay. The hyperlinks are not necessarily still active today.

1. G. Domer, et al., "Gene- and environment-dependent neuroendocrine etiogenesis of homosexuality and transsexualism," Experimental and Clinical
   Endocrinology, 98,141-150, (1991).
2. N. Geschwind & O. Behan, "Laterally, hormones, and immunity." In N. Geschwind & A. Galaburda, Eds., "Cerebral dominance: The biological foundations," (Pages 221-233). Harvard University Press, (1984).
3. "Atopic dermatitis is a hereditary and distinct type inflammatory skin disease which may be associated with other atopic manifestations such as asthma, hay fever, and vernal conjunctivitis." See: http://web.inonu.edu.tr/
4. J.F. Orlebeke, "Elevated sinistrality in Transsexuals," Neuropsychology, Vol 6, #4, Pages 351-355, (1992). This is a PDF file.
5. H. Schneider, J. Pickel, & G. Stalla, "Typical female 2nd–4th finger length (2D:4D) ratios in male-to-female transsexuals -- possible implications for prenatal androgen exposure". Psychoneuroendocrinology 31 (2): 265–9. Abstract at: http://www.sciencedirect.com/

Copyright © 2007 to 2018 by Ontario Consultants on Religious Tolerance
Original posting: 2007-JUN-08
Latest update: 2018-JUN-20
Author: B.A. Robinson

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