Causes of transsexuality Docter and others, but opposed by Charles Allen Moser, Larry Nuttbrock, Julia Serano, and the World Professional Association for Transgender Health.<section end="factors" /> A 2008 study compared 112 male-to-female transsexuals (both androphilic and gynephilic), mostly already undergoing hormone treatment, with 258 cisgender male controls. Male-to-female transsexuals were more likely than cisgender males to have a longer version of a receptor gene (longer repetitions of the gene) for the sex hormone androgen or testosterone, which reduced its effectiveness at binding testosterone. The androgen receptor (NR3C4) is activated by the binding of testosterone or dihydrotestosterone, where it plays a critical role in
Biology and sexual orientation male sexual orientation. The research consisted of 1,077 homosexual men and 1,231 heterosexual men. A gene named SLITRK6 on chromosome 13 was identified, and contains an area or DNA sequence which is different for gay men than for heterosexual men. The research supports another study which had been done by Simon levay. Levay's research suggested that the hypothalamus of gay men is different from straight men. The SLITRK6 is active in the mid-brain where the hypothalamus is. The researchers found another gene, named "thyroid stimulating hormone receptor" (TSHR) on chromosome 14 which dna sequence is different also for gay men.