As noted above, there is only one morphological study on untreated nonhomosexual transsexuals in the literature (Savic & Arver, 2011). This study and our proposed phenotypes for homosexual MtFs and FtMs could help us take the first steps in discerning between homosexual and nonhomosexual transsexuals. Homosexual MtFs are female-like in a series of sexually dimorphic behaviors, while nonhomosexual MtFs are not (Blanchard, 1989a, 1989b). It has also been hypothesized that the brain of homosexual and nonhomosexual MtFs would differ from that of males in different ways. In homosexual MtFs, the differences would involve sexually dimorphic structures and the nature of the differences would be a shift toward the female-typical patterns, while in nonhomosexual MtFs the differences themselves would not involve sexually dimorphic structures (Blanchard, 2008). Moreover, it was also suggested that “if there is any neuroanatomic intersexuality, it is in the homosexual group” (Blanchard, 2008).
Following this line of thought, Cantor (2011, 2012, but also see Italiano, 2012) has recently suggested that Blanchard’s predictions have been fulfilled in two independent structural neuroimaging studies. Specifically, Savic and Arver (2011) using VBM on the cortex of untreated nonhomosexual MtFs and another study using DTI in homosexual MtFs (Rametti et al., 2011b) illustrate the predictions. Cantor seems to be right. Nonhomosexual MtFs present differences with heterosexual males in structures that are not sexually dimorphic (Savic & Arver, 2011), while homosexual MtFs (as well as homosexual FtMs) show differences with respect to male and female controls in a series of brain fascicles (Rametti et al., 2011a, 2011b). If other VBM and CTh studies on the cortex of homosexual MtFs are added (Simon et al., 2013; Zubiaurre-Elorza et al., 2013), there is a more substantial number of untreated homosexual MtFs and FtMs that fulfill Blanchard’s prediction but still only one study on nonhomosexual MtFs; to fully confirm the hypothesis, more independent studies on nonhomosexual MtFs are needed. A much better verification of the hypothesis could be supplied by a specifically designed study including homosexual and nonhomosexual MtFs.