"All people are not heterosexual. Heterosexuality is not superior and is not the norm by which all other sexual orientation and gender identities are measured." --Burnaby, B.C. Schools Draft Policy #5.45

Monday, March 9, 2015

List of Studies

Among the studies that I'm aware of, there are at least a few that are missing from this list. I will add them as I find them. I will also try to think of ways to improve the list, such as inserting a description of the sample size or linking to the full text, where it might be available elsewhere online. I also want to check this list several times more for any errors on my part. 

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Date:  January 2015
Journal name:  Psychoneuroendocrinology

Significant quote from abstract:  "Our findings thus indicate that GM distribution and regional volumes in [gender dysphoric] adolescents are largely in accordance with their respective natal sex. However, there are subtle deviations from the natal sex in sexually dimorphic structures, which can represent signs of a partial sex-atypical differentiation of the brain[.]"

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Date:  November 2014
Journal name:  Journal of Neuroscience 
Study title:  White matter microstructure in transsexuals and controls investigated by diffusion tensor imaging.
First listed author: GS Kranz

Significant quote from abstract: "Results showed widespread significant differences in mean diffusivity between groups in almost all white matter tracts. [Female controls] had highest mean diffusivities, followed by FtM transsexuals with lower values, MtF transsexuals with further reduced values, and [male controls] with lowest values."

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Date:  November 2014
Journal name:  Archives of Sexual Behavior

Significant quote from abstract: "This sex difference, however, was not present in the GID [gender identity disorder] groups. Boys with GID showed stronger, more female-typical CEOAEs whereas girls with GID did not differ in emission strength compared to control girls."

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Date:  September 2014
Journal name:  Cerebral Cortex
Study title:  Structural Connectivity Networks of Transgender People.
First listed author: A Hahn

Significant quote from abstract: "Specifically, our data suggest that network parameters may reflect unique characteristics of transgender patients, whereas local physiological aspects have been shown to represent the transition from the biological sex to the actual gender identity."

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Date:  March 2014
Journal name:  Journal of Sexual Medicine
Study title:  The (CA)n polymorphism of ERβ gene is associated with FtM transsexualism.
First listed author: R Fernandez

Significant quote from abstract: "RESULTS: FtMs differed significantly from control group with respect to the median repeat length polymorphism ERβ (P = 0.002) but not with respect to the length of the other two studied polymorphisms. The repeat numbers in ERβ were significantly higher in FtMs than in control group, and the likelihood of developing transsexualism was higher (odds ratio: 2.001 [1.15-3.46]) in the subjects with the genotype homozygous for long alleles.  CONCLUSIONS: There is an association between the ERβ gene and FtM transsexualism. Our data support the finding that ERβ function is directly proportional to the size of the analyzed polymorphism, so a greater number of repeats implies greater transcription activation, possibly by increasing the function of the complex hormone ERβ receptor and thereby encouraging less feminization or a defeminization of the female brain and behavior."

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Date: January 2014
Journal name: Brain Structure and Function
First listed author: Georg S. Kranz

Significant quote from abstract:  "Further, male controls showed a rightward asymmetry in the midcingulate cortex, which was absent in females and MtF transsexuals."

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Date:  2013
Journal name:  Cerebral Cortex
First listed author: Leire Zubiaurre-Elorza

Significant quote from abstract:  "In conclusion, FtMs showed evidence of subcortical gray matter masculinization, while MtFs showed evidence of CTh feminization. In both types of transsexuals, the differences with respect to their biological sex are located in the right hemisphere."

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Date:  August 2013
Journal name:  Journal of Sexual Medicine

Significant quote from abstract: "RESULTS: Boys and girls produced similar amounts of words, but the group MtFs produced significantly more words in the phonetic condition compared to control boys, girls, and FtMs. During the semantic condition, no differences were found. With regard to brain activity, control boys showed more activation in the right Rolandic operculum, a small area adjacent to Broca's area, compared to girls. No significant differences in brain activity were found comparing transsexual adolescents, although sub-threshold activation was found in the right Rolandic operculum indicating a trendwise increase in activation from control girls to FtMs to MtFs to control boys. CONCLUSIONS: The better performance of MtFs is consistent with our expectation that MtFs perform better on female-favoring tasks. Moreover, they produced more words than girls and FtMs. Even though a trendwise linear increase in brain activity between the four groups only approached significance, it may indicate differences in individuals with gender identity disorder compared to their birth sex. Although our findings should thus be interpreted with caution, they suggest a biological basis for both transgender groups performing in-between the two sexes."

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Date:  August 2012
Journal name:  Journal of Behavioral and Brain Science
Study title:  Increased Cortical Thickness in Male-to-Female Transsexualism.
First listed author: E Luders

Significant quote from abstract: "RESULTS: Results revealed thicker cortices in MTF transsexuals, both within regions of the left hemisphere (i.e., frontal and orbito-frontal cortex, central sulcus, perisylvian regions, paracentral gyrus) and right hemisphere (i.e., pre-/post-central gyrus, parietal cortex, temporal cortex, precuneus, fusiform, lingual, and orbito-frontal gyrus). CONCLUSION: These findings provide further evidence that brain anatomy is associated with gender identity, where measures in MTF transsexuals appear to be shifted away from gender-congruent men."

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Date:  October 2011
Journal name:  Journal of Comparative Neurology

Significant quote: "In the second experiment the MtF transsexual group presented an intermediate value for the total InM neuron number and volume that did not seem different in males and females. Because the CAS group [men who had been castrated due to prostrate cancer] did not have total neuron numbers that were different from the intact males, the change in adult circulating testosterone levels does not seem to explain the intermediate values in the MtF group." 

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Date: October 2011
Journal name:  Archives of Sexual Behavior
First listed author: James M. Cantor

Significant quote from study: "[T]he brains of both homosexual and heterosexual male-to-female transsexuals probably differ from the brains of typical heterosexual men, but in different ways. In homosexual male-to-female transsexuals, the difference does involve sex-dimorphic structures, and the nature of the difference is a shift in the female-typical direction. If there is any neuroanatomic intersexuality, it is in the homosexual group. In heterosexual male-to-female transsexuals, the difference may not involve sex-dimorphic structures at all, and the nature of the structural difference is not necessarily along the male–female dimension."

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Date: July 2011
Journal name: Journal of Psychiatric Research
First listed author: G Rametti

Significant quote from study: "Our results show that the white matter microstructure pattern in untreated MtF transsexuals falls halfway between the pattern of male and female controls. The nature of these differences suggests that some fasciculi do not complete the masculinization process in MtF transsexuals during brain development."

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Date: February 2011
Journal name: Journal of Psychiatric Research
Study title:  White matter microstructure in female to male transsexuals before cross-sex hormonal treatment. A diffusion tensor imaging study
First listed author: G. Rametti

Significant quote from abstract: "Our results show that the white matter microstructure pattern in untreated FtM transsexuals is closer to the pattern of subjects who share their gender identity (males) than those who share their biological sex (females). Our results provide evidence for an inherent difference in the brain structure of FtM transsexuals."

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Date:  May 2010
Journal name:  Journal of Sexual Medicine  

Significant quote from abstract: "Our results confirmed previously reported deviances of brain activation patterns in transsexual men from men without GID and also corroborated these findings in a group of transsexual patients receiving cross-sex hormone therapy. The present study indicates that there are a priori differences between men and transsexual patients caused by different neurobiological processes or task-solving strategies and that these differences remain stable over the course of hormonal treatment."

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Date: 2009
Journal name: Journal of Sexual Medicine
First listed author: ER Gizewski

Significant quote from abstract: "We revealed a cerebral activation pattern in MTF transsexuals compared with male controls similar to female controls during viewing of erotic stimuli, indicating a tendency of female-like cerebral processing in transsexualism."

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Date:  July 2009
Journal name:  Neuroimage
Study title:  Regional gray matter variation in male-to-female transsexualism.
First listed author: E Luders

Significant quote from abstract: "These findings provide new evidence that transsexualism is associated with distinct cerebral pattern, which supports the assumption that brain anatomy plays a role in gender identity."

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Date: January 2009
Journal name: Biological Psychiatry
First listed author: Lauren Hare

Significant quote from study: "In conclusion, our findings indicate a significant association between male-to-female transsexualism and the long polymorphism for the AR repeat."

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Date:  December 2008
Journal name:  Brain

Significant quote from abstract: "We showed for the first time that INAH3 volume and number of neurons of male-to-female transsexual people is similar to that of control females. The female-to-male transsexual subject had an INAH3 volume and number of neurons within the male control range, even though the treatment with testosterone had been stopped three years before death. The castrated men had an INAH3 volume and neuron number that was intermediate between males (volume and number of neurons P > 0.117) and females (volume P > 0.245 and number of neurons P > 0.341). There was no difference in INAH3 between pre-and post-menopausal women, either in the volume (P > 0.84) or in the number of neurons (P < 0.439), indicating that the feminization of the INAH3 of male-to-female transsexuals was not due to estrogen treatment. We propose that the sex reversal of the INAH3 in transsexual people is at least partly a marker of an early atypical sexual differentiation of the brain and that the changes in INAH3 and the BSTc may belong to a complex network that may structurally and functionally be related to gender identity."

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Date: August 2008
Journal name: Cerebral Cortex
First listed author: H. Berglund

Significant quote from study: "In summary, albeit the present study does not provide conclusions concerning the possible etiology, it suggests that in transsexuals the organization of certain sexually dimorphic circuits of the anterior hypothalamus could be sex atypical. It adds a new dimension to our previous reports by showing that the observed effects are not necessarily learned and that a sex-atypical activation by the 2 putative pheromones may reflect neuronal reorganization."

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Date: July 2002
Journal name:  Behavioral Genetics
First listed author:  FL Coolidge

Significant quote from abstract: "Overall, the results support the hypothesis that there is a strong heritable component to GID. The findings may also imply that gender identity may be much less a matter of choice and much more a matter of biology."

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Date:  May 2000
Journal name: Journal of Clinical Endocrinology and Metabolism

Significant quote from abstract: "The number of neurons in the BSTc of male-to-female transsexuals was similar to that of the females (P = 0.83). In contrast, the neuron number of a female-to-male transsexual was found to be in the male range. Hormone treatment or sex hormone level variations in adulthood did not seem to have influenced BSTc neuron numbers. The present findings of somatostatin neuronal sex differences in the BSTc and its sex reversal in the transsexual brain clearly support the paradigm that in transsexuals sexual differentiation of the brain and genitals may go into opposite directions and point to a neurobiological basis of gender identity disorder."

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Date:  August 1998
Journal name:  Psychoneuroendocrinology
Study title:  Cognitive ability and cerebral lateralisation in transsexuals.
First listed author: PT Cohen-Kettenis

Significant quote from abstract: "The results on different tests show that gender differences were pronounced, and that the two transsexual groups occupied a position in between these two groups, thus showing a pattern of performance away from their biological sex. The findings provide evidence that organisational hormonal influences may have an effect on the development of cross-gender identity."

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Date: November 1995
Journal name: Nature
First listed author: JN Zhou

Significant quote from abstract "A female-sized BSTc was found in male-to-female transsexuals. The size of the BSTc was not influenced by sex hormones in adulthood and was independent of sexual orientation. Our study is the first to show a female brain structure in genetically male transsexuals and supports the hypothesis that gender identity develops as a result of an interaction between the developing brain and sex hormones."

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