Abstract
The Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV) describes gender identity disorders as a heterogeneous group of disorders whose common features are:
A strong and persistent cross-gender identification which is manifested by symptoms such as a stated desire to be the other sex, desire to live or be treated as the other sex or the conviction that he or she has the typical feelings and reactions of the other sex.
Persistent discomfort with his or her sex, or a sense of inappropriateness in the gender role of that sex. The disturbance is manifested by symptoms such as preoccupation with getting rid of primary and secondary sex characteristics (e.g. request for hormones, surgery or other procedures to physically alter sexual characteristics to simulate the other sex) or belief that he or she was born the wrong sex.
No concurrent physical intersex condition.
Clinically significant distress or impairment in social, occupational, or other important areas of functioning [1].
The true prevalence of this disorder is unknown, but it is rare, especially in females. The male to female ratio is estimated to be from 30:1 to 6:1. In the USA, about one per 30 000 men and one per 100 000 women seek sex reassignment surgery [2].
A variety of aetiologies have been proposed for transsexualism. There may be some biological factors in this disorder such as increased frequency of poly-cystic ovaries in female-to-male transsexualism [3], anomalous response to oestrogens in male transsexualism [4] and oligomenorrhea and amenorrhea in female-to-male transsexualism [3]. There may be an androgen excess acting on the brain as early as the critical differential period [5]. Chromosomal studies have not shown any apparent abnormality in most cases, although Cryan [6] reported transsexualism in a Kleinfelter (XXY) male. Genetic factors have not been considered to play a role in transsexualism. On the other hand many studies insist that the sex of assignment and rearing is a very important factor in sexual identity [7–9]. Social learning theories focus on the differential reinforcement of sex-typed behaviours, starting shortly after birth. However, sex differences are reported early in life, probably before any major differential impact of parental reinforcement.
The occurrence of transsexualism in female monozygotic twins, in addition to its extreme rarity, shows the probable role of genetic factors in pathogenesis of the disorder.
Case report
The first patient TA, an 18-year-old, single female was referred to Roozbeh Hospital for psychiatric evaluation and admitted upon request.
She revealed that since the age of 3 years, she had had strong masculine tendencies; disliking playing with girls and always wanted to join in with boys in their games. After repeated failure in her exams, she left high school. During adolescence her desires and consequently her relational problems increased. She insisted on dressing herself in men's clothes and having her hair cut short, resembling a young boy. In her relations with same-age peers, she acted as if she were a boy; preferring to date girls, fantasising about having female partners, and even trying to make love with some of her same-sex friends and ex-classmates.
Two years prior to assessment she was arrested and charged with attempts to sexually harass an unknown girl. She denied being a lesbian and insisted that she was born incorrectly and should have been a boy and requested gender reassignment surgery.
Her thought content was not delusional and she had no other symptoms such as formal thought disorder or hallucinations, so schizophrenic disorder or pseudo-transsexualism (somatic delusions) could be ruled out. Her intelligence was evaluated as borderline.
The patient's twin sister was identical to her in physical appearance, and had similar feelings and beliefs; she hated being a girl and also desired sex reassignment surgery. She explained that as far as she remembered, she had shared such feelings with her sister, and that sometimes they ran away from school to date girls. She used to wrap her breasts tightly, believing that it would prevent their growth. Her IQ and education were similar to her twin sister. Although the twins were intellectually borderline and imitative behaviour and twin identification do occur frequently, their transsexual tendencies were not delusional and there was no evidence of a shared delusional disorder.
In physical examination both had completely normal female genitalia. Gynaecological examination confirmed the existence of normal uterus and ovaries. The breasts were underdeveloped, but other secondary sexual traits were normal and feminine. Hormonal studies, skull X-ray, ultrasound of the genitalia and adrenals were in the normal range. Cytological assays displayed an XX female karyotype in both sisters.
The sisters were reared in a broken family. Their mother had two prior unsuccessful marriages, both ending in divorce. In each marriage she gave birth to unwanted children, all being girls and resented strongly. In her third marriage she was hopeful of having a son and after giving birth to the twins, she suffered great disappointment and frustration. When the infants were very young, the marriage broke up and she left home and turned to prostitution. The twin sisters' father rejected them and they were sheltered in an orphanage in the first years of life. Their father married again and their stepmother returned the twin sisters to their home. Their father died when the twins were aged 10 and they subsequently lived in a tumultuous environment, continually being opposed and rejected by their stepmother.
After initial evaluation they were discharged, but they did not return for further therapeutic interventions, including gender reassignment, and were lost to follow-up.
Discussion
Twins concordant for transsexualism is a very rare phenomenon, especially female monozygotic ones. Review of psychiatric literature supports this view: Stoller and Baker [10] reported an identical twin male concordant for transsexualism without seeing the subjects. McKee et al. [11] reported transsexualism in two of three male triplets. A male monozygotic twin pair concordant for transsexualism, but discordant for schizophrenia has been reported by Hyde and Kenna [12]. Garden and Rothery [13] reported a female monozygotic twin pair discordant for transsexualism. Green and Stoller [14] reported two pairs of identical twins (first set two boys and the second two girls) discordant for transsexualism. A pair of transsexual non-twin sisters was reported by Joyce and Ding in 1985 [15].
Most authors reporting transsexualism in twins have concluded that social upbringing and family dynamics play the major role in the pathogenesis of the disorder and rejected any genetic basis for it [13–17]. This case suggests that transsexualism is a very complex phenomenon and interaction of both environmental and biological factors may be necessary for its development.
The history of these twins showed genuine transsexual beliefs in both of them. Their background consisted of living in an unstable and insecure environment. On the other hand, it could be argued that presence of transsexual attitudes in a monozygotic twin without any evidence of other psychiatric disorders such as shared delusional disorder may suggest that a common (yet unidentified) genetic and biological tendency in both of them had contributed to the formation of those attitudes.
Conclusion
Transsexualism in a pair of monozygotic twin suggests that a biological (especially genetic) predisposition may have an aetiological role in this disorder.