 A 2008 study compared 112 male-to-female transsexuals (MtFs), both androphilic and gynephilic, and who were 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 the forming of primary and secondary male sex characteristics.