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From Section 19.3 Gender Identity Disorders of the Comprehensive
Textbook of Psychiatry, Seventh Edition (2000) (section contributed by
Richard Green, M.D., J.D. and Ray Blanchard, Ph.D.):
SUBTYPES
<snip>
DSM-IV subtypes are
(1) sexually attracted to males
(2) sexually attracted to females
(3) sexually attracted to both
(4) sexually attracted to neither
<snip>
ETIOLOGY
Much empirical evidence suggests that the three main types of nonhomosexual
gender identity disorder in males (heterosexual, bi
sexual, and asexual) are superficially variant forms of the same condition; that
nonhomosexual and homosexual gender identity disorder
are etiologically different conditions; that nonhomosexual gender identity
disorder is etiologically related to transvestic fetishism; and
that homosexual gender identity disorder is etiologically related to typical
homosexuality.
The conclusion that heterosexual, bisexual, and asexual gender identity
disorders are superficially variant forms of the same condition is based on a
wide variety of evidence. Similar majorities of men with heterosexual, bisexual,
and asexual gender identity disorder acknowledge some history of transvestic
fetishism; such self-reports are rare in men with homosexual gender identity
disorder. Men with heterosexual, bisexual, and asexual gender identity disorder
are also similar to each other, and dissimilar to men with homosexual gender
identity disorder with regard to their degree of recalled childhood femininity,
age at clinical presentation, extent of interpersonal heterosexual experience,
and a history of erotic arousal in association with thoughts of being a woman.
It is possible that the common denominator linking transvestic fetishism and
heterosexual, bisexual, and asexual gender identity disorder is autogynephilia,
a male's tendency to be sexually aroused by the thought or image of himself as a
woman. Autogynephilia is highly variable in its manifestations. It may be
expressed in fantasies of dressing as a woman (transvestic fetishism); in
(masturbatory) fantasies of engaging in stereotypically feminine behavior like
knitting; in fantasies of gestating, lactating, or menstruating; in fantasies of
being treated by other people as a woman; or in fantasies of possessing a
woman's body. When an autogynephilic man's favorite sexual fantasy is that of
possessing a vagina, he is very likely to develop cross-gender wishes that
persist even when he is not sexually aroused, along with a desire for surgical
sex reassignment.
Autogynephilia may be conceived as a modified form of heterosexuality, in which
a man's sexual approaches are directed not at external women but at a feminized
version of himself. It seems to involve some developmental anomaly in the
learning of sexual behavior, because the man's principal erotic object in many
cases-for example, the thought or image of himself wearing pantyhose, applying
make-up, or knitting-cannot be innate but must have been assembled from
experiences. It remains to be discovered whether some men are relatively prone
to such developmental anomalies for neurological reasons.
The conclusion that homosexual gender identity disorder and typical
homosexuality (i.e., homosexuality without gender identity disorder)
have etiological commonalities is based on two lines of evidence. The first is
that the early manifestations and homosexual gender identity disorder appear
rather similar. Research has consistently shown that at least 50 percent of
asexual men with no gender identity problems nonetheless recall significant
amounts of cross-gender behavior in childhood. Similar although somewhat less
striking findings obtain for homosexual women. These observations suggest that
the difference between ordinary homosexuality and homosexual gender identity
disorder begin as a difference in degree, which develops during adolescence into
a difference in kind, when the less severely affected children shed their
cross-gender traits and the more severely affected children elaborate them into
a full-blown cross-gender identity. The second line of evidence is
epidemiological in nature and pertains only to males. Research on homosexual men
without gender identity disorders has established that homosexual men are on
average born later in the sibling order than comparable heterosexual men. Recent
studies have established that this difference in birth order is caused by
homosexual males having a greater number of older brothers; they do not have a
greater number of older sisters, once their number of older brothers has been
taken into account. Studies of Dutch, Canadian, and British male patients with
gender identity disorder have produced the
similar finding that homosexual patients are on average born later than
nonhomosexual patients. These observations suggest that whatever
etiological factor is reflected by high birth order contributes to the
development both of homosexuality and of homosexual gender identity disorder.
The foregoing discussion illustrates that theories developed to explain
homosexuality or transvestic fetishism may also apply to homosexual or
nonhomosexual gender identity disorder respectively. Furthermore, theories
developed to explain gender identity disorder without further qualification may
apply to only one of the two main types.
BIOLOGICAL FACTORS
Theories of homosexual development, notably in males, have taken on an
increasingly biological basis as opposed to an experiential one.
Genetic Factors
The Franz Kallmann twin study of the 1950s found a 100 percent concordance for
homosexuality between presumably monozygotic male twins. Further research
indicated discordant pairs, and methodological critiques of the Kallman study
resulted in a general decline of interest in the genetic basis. However, in
recent years twin studies and other family studies of sexual orientation have
promoted new interest. A 1991 study of 56 male monozygotic pairs of twins raised
together found a 52 percent concordance for homosexuality compared with 22
percent for 54 dizygotic pairs. A 1992 study found that of 71 female monozygotic
twin pairs, 48 percent were concordant for homosexuality or bisexuality compared
with 16 percent for 37 dizygotic pairs. Monozygotic twins separated at birth,
although rare, provide a better model for testing the relative influences of
environment and genetics than do twins reared together, where the two factors
are confounded. A report of two pairs of males separated at birth argues for an
inherited influence on homosexual orientation. In one pair, both men were
homosexually oriented. In the second pair, one twin was homosexual, and the
other, while heterosexually married, had had a 3-year homosexual relationship in
adolescence. By contrast, in four pairs of separated female-female twins where
one twin in each pair was lesbian, none of the cotwins was lesbian.
Family studies of nontwin siblings of homosexual men and women also lend support
to a genetic basis, although the confound of a similar environment is
considerable. Two studies found higher rates of homosexuality in brothers than
is expected in the general male
population. No corresponding increase in the number of lesbian siblings was
reported. Two gene linkage studies add further weight to a genetic basis of male
homosexuality. When families are selected for having male homosexuals on the
mother's side of the family tree, and two of the mother's sons are homosexual,
there is an increased probability of a marker for a shared gene on the sons' X
chromosome (contributed by the mother). The marker is less often shared between
a homosexual and a heterosexual brother.
Hormonal Factors
Evidence for a hormonal influence on gender identity disorder derives from
several research sources. One possible source is congenital virilizing adrenal
hyperplasia. Girls his condition overproduce adrenal androgen from before birth.
They are more rough-and-tumble, less interested in doll play, and likely to be
considered tomboys than girls without the condion. Conversely, there is limited
evidence that prenatal exposure of males to estrogenic or progestational agents
may reduce the expression of conventional boy-type behaviors. Atypical levels of
sex-typed hormones before birth and the attendant effects on specific sex-typed
behaviors can substantially modify the child's early social experiences. Boys
who are disinclined to rough-and-tumble play or who play with dolls have
different father-son and mother-son relationships and a different peer group
experience from more conventionally masculine
boys. Similarly, girls who prefer rough-and-tumble activity and sports to doll
play have a different early socialization experience with
parents and peers from girls who are conventionally feminine. Thus, hormonal
influences may act through a pathway of affecting sex-typed behaviours that
interact with socialization experiences. Reported neuroendocrine and
neuroanatomical differences also suggest an inborn contribution to sexual
orientation, particularly in men. One phenomenon tested is the feedback response
on luteinizing hormone (LH) after an intravenous pulse of estradiol. In women
there is a marked rebound after an initial drop (the hormonal basis of
ovulation). The original research found an attenuated female-like response in
homosexual men, which theoretically reflected a deficiency in prenatal
androgenization of the central nervous system (CNS). In another study using the
same methodology, more than a sample of homosexual men showed a response more
like that of the heterosexual women than of the heterosexual men in the study.
However, a subsequent study, which used a different approach to elicit the
luteinizing hormone feedback
phenomenon, found no significant group difference, and another study with a
methodology similar to that used in the original research also failed to confirm
a difference. A related phenomenon that suggests that a deficiency in male in
utero leads to a homosexual orientation in men derives from the prenatal stress
theory.
Stressing pregnant rodents results in feminized behavior in male offspring,
owing either to the competition between adrenal stress
steroids and testicular androgens or to the mistiming of testicular androgen
secretion as a result of stress. In one study a higher-than-average rate of
homosexuality was found in men who were born in Germany between 1941 and 1946,
the stressful years of World War II. However, an environmental explanation is
also possible, because fathers were more likely to be away from their sons
during the war. A second study, based on retrospective reports by homosexual,
bisexual, and heterosexual men describing stress in their mothers, found more
stress during the pregnancies of the mothers of homosexual men. Other research
has been less supportive of an association between stress and homosexuality.
Some research found no connection. One American study found a marginally
significant relationship, based on the reports of mothers of college students.
Another found a low correlation between reported pregnancy stress and
lesbianism, but not with male homosexuality. No prospective studies are
reported. Although medical histories given by parents of children with gender
identity disorder do not provide a basis for grossly abnormal hormone levels
before birth, a neuroendocrine base may still be posited at a more subtle level.
If the range of prenatal androgen levels is as wide
as that in adult life, the fetus may also be exposed to a wide range of
androgen. Another factor could be the androgen surge that occurs in boys between
about 3 weeks and 3 months of age.
Immunological Theories
Two immunological theories have been advanced to explain the finding that
homosexual men (including those with gender dysphoria of the homosexual subtype)
have a greater average number of older brothers than do heterosexual men. Both
theories propose that male homosexuality may result from a maternal immune
reaction, which is provoked only by male fetuses and which becomes stronger
after each pregnancy with a male fetus. The earlier theory proposed that
antibodies to testosterone, produced by a woman pregnant with a male fetus and
passed through the placenta from the mother to the fetus, could reduce the
hormone's biological activity and thus compromise the sexual differentiation of
the fetal brain. This seems unlikely because steroid hormones are not ordinarily
antigenic. An alternative theory is that the relevant fetal antigen might be one
of the male-specific, Y-linked, minor histocompatibility antigens, often
referred to collectively as H-Y antigen. Although there is no direct evidence
for this theory, it is consistent with a variety of observations, including the
finding that male mice whose mothers were immunized to H-Y prior to pregnancy
are much less likely to mate successfully with receptive females.
Brain and CNS Involvement
A difference in a nucleus of the anterior hypothalamus may represent a CNS
difference related to sexual orientation. The area known as
interstitial nucleus of the anterior hypothalamus-3 (INAH-3) was compared in
autopsy between homosexual men, heterosexual men, and
heterosexual women. Although there was some overlap between the size of the
nucleus between the groups, it was smaller on average in the homosexual men and
women compared with the heterosexual men. All the homosexual men and some of the
heterosexual men and women had died of acquired immune deficiency syndrome
(AIDS), but death from AIDS was not a factor. No homosexual women were studied
to determine whether the size of their nucleus was similar to that of the
heterosexual men. INAH-3 is embedded in the hypothalamic area that appears to be
related to some aspects of sexual behavior in male nonhuman primates. This study
has neither been confirmed nor refuted by subsequent research. Another finding,
of a larger suprachiasmatic nucleus in a sample of homosexual
men, may be less relevant because that area is not known to be associated with
sexual behavior. However, it may be related to endocrine function. A more recent
finding points to a difference in the brain of male-to-female transsexuals. In a
post mortem sample of 6, the bed nucleus corresponded in size to that of typical
females rather than to that of typical males; it was not relevant whether the
male transsexual was heterosexual or homosexual.
Psychosocial Theories
Psychodynamic and behavioral influences may lead to extensive cross-gender
identification. In an early study boys with an excessive
mother-son symbiosis in the early years, replete with extensive mother-son
skin-to-skin contact, appeared later to manifest significant
feminine behavior. This is attributed to the inability to differentiate
psychologically from the mother. Male- identified females have been
reported to have mothers who were removed in affect from their children,
frequently by depression, and fathers who did not support their
daughters' femininity. The girl becomes a substitute husband to treat the
mother. Other reports describe traumatic psychological losses to boys and girls
in the earliest years that appear related to the onset of cross-gender behavior.
Research on a sample of 66 boys with gender identity disorder found a positive
correlation between the extent to which parents supported cross-gender behaviors
in their sons and the extent of that cross-gender behavior. In most of the
families at least initially there was no discouragement of cross-gender
behaviors. In more limited work with girls with gender identity disorder,
initial parental reactions were similar. A study of cross-gendered boys found
the extent of father-son involvement in the early years to be related to later
sexual orientation. The association emerged not only between the two groups of
boys studied (gender identity disorder and control) but within the subgroup of
boys with gender identity disorder. Less father-son involvement was associated
with a more homosexual orientation.
Social Learning Theories
Social learning theories typically focus on the differential reinforcement by
parents of sex-typed behaviors, starting shortly after
birth. This reinforcement shapes conduct into conventional masculinity or
femininity. Cause and effect are hard to distinguish here. On the one hand, sex
differences are reported early in life, probably before any major differential
impact of parental reinforcement; on the other hand, mothers and fathers
apparently treat male and female newborns differently.
In Baby X experiments adults are told, sometimes incorrectly, the sex of a
clothed child and asked to describe the child's attributes or to
provide it with toys. Perceived boys are encouraged more to physical action and
are given more whole-body stimulation than perceived girls. When 6-month-old
children were similarly clothed, toy choice by adults was related to perceived
gender of the child. Boys were presented with footballs, girls with dolls.
Strong bald babies were seen as male, soft fragile ones as female. At 1 year,
boys may be more exploratory and active and toy preferences may differ. Girls
were found to prefer soft toys and dolls whereas boys preferred transportation
toys and robots. A preference for same-sex playmates emerges early. When 31/2-
to 41/2-year-olds were shown
photographs of boys and girls and asked to select those with whom they would
like to play, boys preferred boys and girls preferred girls. By age 2 to 3
years, boys appear to be more aggressive toward peers and to show more
rough-and-tumble play. Fathers are as likely to give a 1-year-old daughter a
truck as a doll but more likely to give the son a truck. However, when children
are given dolls, boys play with them less than girls. Fathers more than mothers
give negative responses to boys playing with dolls. Boys receive more positive
responses for playing with blocks and girls receive more positive responses for
playing with dolls.
Imitative and vicarious learning pervade general theories of social learning
of sex typing. In imitative learning, behaviors are adopted
that simulate those of a significant other person, the model. In vicarious
learning, if something happens to a model the viewer's behavior is modified to
resemble the model because the child perceives the model as possessing desirable
attributes or obtaining desirable
goals. The cognitive developmental theory, by contrast, sees the child first
labeling itself as male or female and then finding the behaviors associated with
that label rewarding.
Nature Versus Nurture
The classic research on intersexed or hermaphroditic children pointed to the
early-life emergences of gender identity as being influenced primarily by
environment and as irreversible. In the studies by John Money, Joan Hampson, and
John Hampson, a range of anatomical features discordant with the gender of
rearing were found to be less relevant to the adoption of a male or female
gender identity than the gender of rearing.
Studies of matched pairs, for example, demonstrate that with the syndrome of
congenital virilizing adrenal hyperplasia, the newborn
female, if considered to be male and designated male, matures with a male
identity in spite of having the XX female chromosomal pattern, ovaries, and a
uterus. If considered female the child matures with a female identity. However,
questions have been raised about the generalizability of those findings to
nonintersexed children because of the atypical prenatal endocrine environment
and other atypical genetic or anatomical influences of intersexed children.
Studies of children born with normal sex characteristics who undergo gender
reassignment early in life may be a more relevant test of nature versus nurture.
The tragedy of penile amputation, usually through negligent circumcision, has
provided such a model. In one celebrated case a reassigned male monozygotic twin
who was reportedly being raised successfully as a girl failed to incorporate a
female identity and now lives as a heterosexual male. Reassignment in that case
was at 22 months, which may have been after core identity as a male was in
place.
A somewhat more complicated outcome was revealed in the very recent psychosexual
follow-up of another biologically normal male whose penis was accidentally
ablated during circumcision at the age of 2 months. The decision to reassign as
a female occurred sometime between 2 and 7 months, at which point surgical
castration occurred. At age 26 years, clinical interviews and self-report
questionnaires were used to obtain information on the patient's gender identity,
gender role, sexual orientation, and sexual identity. In adulthood the patient
lived socially as a woman and her gender identity was unequivocally female, with
no evidence of gender dysphoria. However, the patient's childhood gender role
behavior had been predominantly masculine, and her current
occupation was male-dominated. Moreover, she fantasized sexually about women
more often than about men. On the other hand, her objective sexual history
included roughly equal amounts of sexual experience with women and men. At the
last follow-up, the patient was living with a new female partner, in a lesbian
relationship.
Psychoanalytic Theories
As in other areas of pathology, psychoanalytic theories about gender identity
disorder constitute a tradition distinct from biological and
other nonbiological approaches. One influential theory is that of Ethel Person
and Lionel Ovesey, who advanced the hypothesis that
transsexualism in males originates from unresolved separation anxiety during the
separation-individuation phase of infantile development. To cope with this
anxiety, the child resorts to a reparative fantasy of symbiotic fusion with his
mother. Adult transsexualism may be understood as an attempt to master that
anxiety through sex reassignment surgery, through which the transsexual acts out
his unconscious fantasy and symbolically becomes his mother.
According to this hypothesis, male transsexuals vary in the directness with
which they proceed to the transsexual resolution. Some individuals never develop
any other psychosexual phenomena as defenses against separation anxiety, and
they proceed to the transsexual outcome in a straightforward manner. Others
develop transvestism or effeminate homosexuality as initial defenses. When those
defenses fail in the face of various stressors, the individual regresses to the
primitive fantasy of symbiotic fusion with his mother and begins to experience
transsexual impulses.
The other major psychoanalytic theory was developed by Robert Stoller to explain
the etiology of transsexualism in a specific group of biological males, who
would fall within the DSM-IV category of gender identity disorder, sexually
attracted to males. Stoller called those males true transsexuals.
The theory begins with the grandmother of the future transsexual who treats her
daughter coldly and neither encourages nor models femininity for her. The
grandfather has a closer relationship with the daughter, but he encourages
masculinity in her. In consequence the mother of the future transsexual develops
a mild gender identity disorder of her own. In adolescence, however, she
abandons her conscious transsexual wishes of someday being male and adopts a
heterosexual façade. At the unconscious level she nevertheless retains a strong
penis envy. The transsexual's mother eventually enters an empty and marriage
with a passive and withdrawn husband who is psychologically if not physically
absent from the household. The final pathogenic process becomes operative when
the mother gives birth to an infant son she perceives as particularly beautiful
and graceful. The boy, who represents her feminized phallus, fulfills her
lifelong wish for a penis. The mother-son interaction, described by Stoller as a
blissful symbiosis, includes excessively close and prolonged body contact,
sometimes with the infant's nude body cradled against the mother's nude body.
The mother's behavior expresses her need to treat her son an extension of her
own body.
The transsexual's early experiences, especially the continuous skin-to-skin
contact, produce an overidentification with his mother, a
blurring of ego boundaries, and eventually a feminine gender identity. The
transsexual boy never develops a "heterosexual" relationship with his
mother and therefore never develops an oedipal conflict. His femininity is
produced nonconflictually and remains a nonconflictual, autonomous form of
behavior. This theory does not account for "secondary" transsexuals,
notably those who evolve through a transvestite, heterosexual pattern.
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