Causes of gender incongruence

The etiology of transsexualism, meaning the cause or causes of transsexualism, is an area of interest for many transsexual people, physicians, psychologists, other mental health professionals, and family members and friends of transsexual people. Currently, the cause of transsexualism is not known. Psychological and emotional factors have been hypothesized. Some research has suggested biological factors in the development of transsexuality.

Possible psychological causes

Many psychological causes for transsexualism have been proposed; including "overbearing mothers and absent fathers", "parents who wanted a child of the other sex", repressed homosexuality, emotional disturbance, sexual abuse, and a variety of sexual perversions and paraphilias, including autogynephilia.

Harry Benjamin wrote, "Summarizing my impression, I would like to repeat here what I said in my first lecture on the subject more than 10 years ago: Our genetic and endocrine equipment constitutes either an unresponsive [or] fertile soil on which the wrong conditional and a psychic trauma can grow and develop into such a basic conflict that subsequently a deviation like transsexualism can result."

Many theories developed to describe transsexual women were even less useful when applied to transsexual men. One such example was Ray Blanchard's theory that all transwomen could be divided into the categories of "autogynephilic" and "homosexual". Many psychological theories had also been applied to homosexual people, also usually without success. This led to theories which considered the possibility of physical reasons for transsexualism.

Experience with individuals who were sexually reassigned at birth, in order to correct deformities such as those caused by accidental castration or intersex conditions, suggests strongly that one's mental gender identity is not determined by the environment they are raised in. Individuals born male but raised as female, or vice versa, often show the same signs of gender dysphoria as transsexual people; rejecting their assigned gender. One notable example was David Reimer. Reimer later suffered depression and heroin addiction in adulthood, which has been taken as proof of gender essentialist biological theories; however, critics of the case study note that his twin brother suffered from the same conditions, and that their depressive moods were likely genetic in origin.

"Curing" transsexualism

Psychological treatments aimed at curing transsexualism are historically known to be unsuccessful. In 1972, the American Medical Association Committee on Human Sexuality published the medical opinion that psychotherapy was generally ineffective for transsexual adults. A number of other treatments have been tested on transsexual people, including aversion therapy, psychotropic medications, hormone treatments consistent with the patient's birth sex, electroconvulsive therapy, and hypnosis. These treatments have also been shown to be ineffective.

Conversion therapy, which is usually aimed at gay and lesbian people, has also been applied to transsexual and transgender people. The Kinsey scale once expressed a view of transsexualism as an extreme form of homosexuality; the medical community now rejects this part of Kinsey's theory. Conversion therapy is generally ineffective for transsexual and transgender people as well as gay and lesbian people. Even though many major medical and psychological associations have condemned conversion therapy as not only ineffective, but actually harmful, it continues to be advocated as a treatment for both homosexual and transsexual people by various organizations in the Western World, often with ties to the conservative Christian movement or other conservative religious movements.

However, for certain transsexual persons, therapies aimed at resolving gender conflicts, other than somatic treatments to reassign physical sex, may be effective and useful. Some people may have milder conflicts between their gender identity and physical sexual characteristics. These people may not wish to pursue sex reassignment therapy, but may seek care to help deal with the conflicts they face. If individuals express the desire for psychological care without plans for sex reassignment surgery, supportive and psychoeducational counseling may be helpful. Additionally, some transsexual people who may have a significant lifelong conflict between gender identity and their sexed body may present for care without requesting SRS. Their reasons for forgoing transition and/or SRS may include family and/or professional concerns, perceptions of the difficulty of transition, fear of loss of social standing or role, religious beliefs, political standpoints, real or perceived inability to finance transition, and advanced age or chronic medical problems, which may, in some cases, be considered medical contraindications to hormone therapy and/or sex reassignment surgery. These individuals often seek alternative methods with which they can improve their functional status, promote acceptance of their gender identity as valid, and ameliorate mood symptoms caused by gender conflict, through psychotherapy, and sometimes with medications. Additionally, these individuals sometimes benefit from partial transition options, such as low dose hormone therapy, validation of the patient's desire to dress and live partially in the gender role consistent with their gender identity, or even simply allowing the person a safe outlet to express themselves as members of their target gender. These options can provide a great deal of comfort to individuals who, for any reason, choose not to fully transition. Such therapies may also benefit people who manifest transsexual-like symptoms but who are not diagnosable as "genuine" transsexual people.

Possible physical causes

A point of empirical evidence that a physical cause may be at hand in transsexualism, is that in the most common accounts of their childhood, transsexual (and also many other transgender) people claim to have had feelings of being either a girl or boy for as long as they are able to remember. As andectodal evidence, it is important to take it with a point of scepticism. However, the medical field for a long time had expected and required accounts such as this in order to receive access to medical treatment.

One study gives strong evidence that transsexualism is based in structural and neurochemical similarities between the brains of transsexual people and brains typical of their gender identity; this study has been alleged to have numerous flaws . A second study has since replicated the results of the first study and included controls to help eliminate many of the alleged flaws, particularly the study included two individuals who had cross-gender hormone secreting cancers which were significant enough to have caused significant cross-gender development in both individuals. Although transsexualism manifests itself as an anomaly in brain structure in which transsexual people have a neuron density in the central subdivision of the Bed Nucleus of the Stria terminalis region (BSTc), similar to members of their target gender, it is not known whether this is a cause, consequence, or simply a manifestation of transsexualism.

As of December 2006, a new study funded by Ferring Pharmaceuticals was presented at the International Paediatric Endocrinology Symposium in Paris. This study finds that prior to hormone replacement therapy, transsexual people have brain mass ratios of their birth sex. According to this study, a transsexual person's brain restructures itself to become typically structured for the individual's target sex with the administration of hormone therapy. This study did not analyze differences in specific sexually dimorphic regions of the brain, rather it focused on large-scale differences in overall brain structure.

Several animal studies have demonstrated that exposure to cross-sex hormones during certain stages of fetal development can reliably produce cross-sex behaviors in animals. In addition, twin studies have demonstrated a strong heritability of transsexualism. This research provides additional evidence that transsexualism may be caused by genetics and in utero hormonal environment. There are several known cases of identical twins who were both transsexual, both male-to-female and female-to-male.

A recent study from Germany provides additional evidence of a physiological basis for transsexualism. The study found a correlation between digit ratio and male-to-female transsexualism. Male-to-female transsexual people were found to have a higher digit ratio than control males, but one that was comparable to control females. Because digit ratio is known to be directly related to prenatal hormone exposure, this tends to support theories linking such to male-to-female transsexualism.

There is also evidence from transsexual people born between the 1930s and 1970s that exposure to a synthetic estrogen known as diethylstilbestrol(DES), routinely used at the time to prevent miscarriage and treat morning sickness, may have contributed to disrupting the hormonal balance within the womb. Evidence suggests that an unusually high percentage of physical males whose mothers were known to have taken this medication present as transgender or transsexual, either in childhood or in later life.

Due to incidents of birth defects and other side effects, the use of DES and other synthetic estrogen compounds has been largely abandoned or replaced with natural estrogens. Today, with widespread use of certain plastics and other substances, there are likely to be many environmental pollutants which closely mimic the chemical structures of the withdrawn drugs. This suggests that prenatal environmental factors could also influence the development of this condition.

A 2005 study found that prenatal exposure to phthalates reduced the anogenital distance in males. Shorter anogenital distances were found to be associated with smaller penises, cryptorchidism, and lower levels of aggressiveness. Although no transsexual patients were included in this study, it suggests that environmental pollutants can affect sexual development in physical males.