Tag Archives: twins

Gender Identity Disorder and Anorexia Nervosa in Male Monozygotic Twins – Review

This is a fascinating study of identical twins; one had gender dysphoria and one did not. Both twins developed anorexia.

Both twins were feminine in behavior from a young age and both were sexually attracted to men. Both had a difficult childhood with an abusive father.

Both twins were underweight at birth and needed intensive care. Both had developmental delays.

However, one twin considered himself to be a gay man while one identified as a straight woman.

In this case study, gender dysphoria did not cause the eating disorder.

This case highlights the importance of other factors in eating disorders, including genes, hormones, and trauma.

It raises the question; how important is gender identity as a cause of eating disorders?

This case is different from other case studies where gender dysphoria seems to be intimately linked to the eating disorder.

We can’t look at these two patients and conclude that gender dysphoria never contributes to eating disorders. However, this case is a good reminder to be cautious about drawing conclusions from other case studies. Perhaps there are just some people with eating disorders who also have gender dysphoria. Or perhaps there is some other factor which causes both eating disorders and gender dysphoria.

As always, we need more studies.

More about the Patients:

Eating Disorders

Twin A was diagnosed with AN-purging subtype and Twin B was diagnosed with AN-restricting subtype.

Twin B developed an eating disorder at an earlier age, but Twin A was more underweight and had a more disturbed perception of his body. Furthermore, Twin A was hospitalized for his eating disorder and Twin B was not.

Neither twin seems to have been able to maintain a healthy weight.

At age 16 Twin A “was admitted to a children’s hospital because of AN. Later, he was hospitalized in the psychiatric inpatient unit for adolescents. At first, his eating behavior was restrictive. Then he reported intermittent vomiting (AN binge-purge). His weight decreased to 46 kg/1.79 m (body mass index [BMI] ¼ 14.3 kg/m²). His ideal weight was 44 kg according to a BMI of 13.7 kg/m² , which shows his severe disturbance in body perception. During hospitalization, his behavior was sometimes aggressive. He was emotionally unstable, depressed, and was rarely able to engage in stable relationships. Despite strict dietary rules, he achieved a maximal weight of 55 kg (BMI ¼ 17.2 kg/m²). Soon after being discharged, his weight decreased again.”

Twin B’s eating disorder began at a younger age. “In puberty, he developed severe underweight. At the age of 13, he was 42 kg/1.58 m (BMI ¼ 16.8 kg/m² ). When he was referred to our outpatient unit at the age of 18½ years [for gender dysphoria], his weight was 48 kg and his height was 1.76 m (BMI ¼ 15.5 kg/m² ). He denied deliberate dieting, binging, or purging. Although he regarded himself as too slim, he did not manage to gain weight. Further medical checkups revealed no somatic cause for his underweight. An osteodensitometry yielded an osteopenia of the spine.”

Gender Identity

Twin A was a gender non-conforming gay male:

In childhood, he preferred girls’ games and toys (Barbie dolls) and was very close to his twin brother. His sexual feelings were always for males. Although he started cross-dressing at the age of about 16 years, his gender identification was always male. He considered himself to be a homosexual.”

Twin B was a trans woman:

“As far as he could remember, he had felt he was a girl, preferring girls as playmates and had started cross-dressing at nursery school. In gymnastic lessons, he refused to change with the other boys because he was ashamed of his body. Eventually, he refused to attend sports lessons at all. When he was 9 years old, he started to grow his hair. His class mates seemed to accept him as a girl. When he started to work as a hairdresser, he tried to correspond to the male gender role and did not cross-dress. However, at his professional school and in his free time, he continued to cross-dress. His employer, who realized he was transsexual, permitted and encouraged him to cross-dress at work, which consequently allowed him to live as a young woman. Sexually, he was always attracted to men. However, in contrast to his brother, he never considered himself to be homosexual and viewed this attraction as ‘‘heterosexual.’’ Until this point, he had not engaged in sexual relationships either with men or with women.”

Twin B requested hormonal and surgical sex reassignment.

Childhood

The twins grew up together in a small Swiss city without any other siblings. Their childhood was not easy:

“[Their father] was very authoritarian. He could not accept the sexual orientation and the cross-dressing of his sons and threatened them with assault and even with death.

…In family conflicts, [their mother] took a position between her husband and her sons. At a family consultation, she appeared emotionally unstable.”

Birth 

The birth was a difficult one. Both twins were underweight and spent time in intensive care.

“the mother had been admitted to a hospital with hypertension, edema, and proteinuria at 38 weeks of gestation. The vaginal delivery was induced because of maternal preeclampsia. Twin A weighed 2.17 kg at delivery and his Apgar score was 9/9/9. Because of perinatal acidosis and hypotonia, he was kept in the incubator for 3 days. He was diagnosed with a subependymal hemorrhage with ventricular invasion. Twin B’s birth weight at delivery was 1.95 kg and his Apgar score was 7/9/9. Both twins were admitted immediately to the neonatal intensive care unit.”

Developmental Delays

They both had developmental delays:

“In early childhood, Twin A showed a developmental delay in language and motor skills and had deficits in cognitive and verbal skills. He was socially isolated and his behavior was often aggressive.”

“…Twin B had delays in language and motor development during early childhood. He showed the typical symptoms of attention deficit and hyperactivity disorder. The parents refused further assessment and treatment.”

Other

Twin A was diagnosed with borderline personality disorder and subnormal verbal intelligence.

Twin B was diagnosed with gender dysphoria.

There is no obvious pattern to any of this. Twin A was larger at birth, but had more problems right after birth. Both had developmental delays, and Twin B may have had ADHD as well. Both were feminine in their behavior, but only Twin B developed gender dysphoria. Both were sexually attracted to men. Twin B developed an eating disorder earlier, but Twin A’s eating disorder seems more severe. Twin A has borderline personality disorder and Twin B does not.

Discussion

The authors offer two possible hypotheses about the twins’ gender identity.

Perhaps the twins are on a continuum of gender non-conformity where gender dysphoria is at the extreme end.

Alternatively, perhaps gender dysphoria* in childhood is inherited, but the later development of gender identity is determined by environmental factors and psychiatric comorbidity.

“In childhood, both Twin A and Twin B showed gender atypical behavior and stereotypical feminine traits and interests. In adolescence, their sexual orientation was revealed to be homosexual. Twin A developed effeminate homosexuality with male gender identity, whereas Twin B stabilized his cross-gender identity. Although Twins A and B are concordant for GID in childhood and sexual orientation on a categorical level, they are now discordant for TS. On a more dimensional level, one could argue that Twins A and B show an opposite sex-dimorphic behavior and that they arrived at different points of a continuum. The fact that GID in childhood is a predictor for later homosexuality and TS could support the dimensional view. It could be hypothesized that GID in childhood is mainly hereditary, whereas the development of the later phenotype of the gender identification is determined by environmental factors and psychiatric comorbidity, as any difference between MZ twins provides strong evidence for the role of environmental influences.”

The authors also discuss the relationship between gender and eating disorders. However, they don’t address the fact that the two twins had different gender identities, but both had eating disorders.

Perhaps both gay men and trans women are vulnerable to eating disorders for different reasons, but perhaps genes, hormones, and environment matter more than gender identity.

“Homosexual men seem to have an increased vulnerability to eating disturbance and body dissatisfaction (Williamson & Hartley, 1998), are more dissatisfied with their weight (French, Story, Remafedi, Resnick, & Blum, 1996), and are more concerned about their attractiveness (Siever, 1994). Male AN is associated with disturbed psychosexual and gender identity development, which supports the hypothesis that males with atypical gender role behavior have an increased risk of developing an ED (Fichter & Daser, 1987). Furthermore, feminine gender traits are discussed as a specific risk factor for ED in men and women (Meyer, Blissett, & Oldfield, 2001). Although the role of sexual orientation as a risk factor for ED is well documented, there is hardly any literature about GID and ED. For men with disturbance of gender identity in addition to the aforementioned factors concerning sexual orientation, underweight could be a way to suppress their libido and the expression of their secondary sexual characteristics and, at the same time, correspond to a female ideal of attractiveness (Hepp & Milos, 2002).”

We need more research!

“Further research in eating behavior and body dissatisfaction in patients with GID could provide more insight into the role of gender identity in the development of ED and lead to a better understanding of ED as well as GID.”

 

* In this case, gender non-conformity might be a more fitting phrase. Twin A does not seem to have ever wanted to be a girl.

 

Original Source:

Gender Identity Disorder and Anorexia Nervosa in Male Monozygotic Twins by Urs Hepp, Gabriella Milos, and Hellmuth Braun-Scharm in Int J Eat Disord. 2004 Mar;35(2):239-43.

 

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Identical Reared apart Twins Concordant for Transsexuality – Review

This is a brief article about a case of identical twins reared apart who both had gender dysphoria. Unfortunately, it is based on an interview with only one of the twins. This makes it a suggestive report, but not scientific proof.

In addition, one of the twins was born with an intersex condition. This raises the question of whether his gender dysphoria was caused by genes or the prenatal environment.

The twins were born male and separated at birth and raised in different families. They did not meet each other until they were 15. DNA testing confirmed that they were identical twins.

This is only one case, so the conclusions we can draw are limited.

The main weakness of the report, however, is that it is based on the memories of only one of the twins, LT. The authors were able to interview LT in his 50s.* It is possible that his memories of meeting his twin AT 35 years ago would be incorrect or might exaggerate similarities or differences.

According to LT,

“Prior to meeting, by age 8 years both twins experienced gender discomfort, engaged in cross-dressing, and felt that they should have been born as the other gender. Also prior to meeting, both twins experienced unease with the anticipated and actual secondary sexual development of puberty. Furthermore, unbeknownst to his twin, at age 14 years LT was fully committed to undergoing sex reassignment surgery and so convinced his mother that she took him to see a urologist.”

According to the author of the report, this means that both twins met the criteria for gender dysphoria, “persistent cross-gender identification and a strong desire to change the sexual characteristics to those of the other gender.”

I am not comfortable with diagnosing someone you have not interviewed. Clearly, AT had some issues with his gender, but how did he define himself? Did he want to have surgery? Did the twins continue to have contact and did AT’s gender dysphoria persist into adulthood? Did they influence each other after age 15?

This report is also about a tragedy. AT committed suicide at age 35.

The twin’s birth mother had skin cancer and doctors believed she should give one twin up for adoption. AT was therefore put in a state-run institution and then adopted by a less well-to-do family. His parents were “religious, punitive, and rejecting of his cross-gendered behaviors.” (Presumably we know all this from his twin, LT.)

LT was raised by his biological parents. His family was more financially comfortable. His mother and sisters “supported his female identity as it developed and afterward.”

The authors of the study stress the importance of family support in preventing suicide, but there are a number of other factors that might have also influenced AT. Adoptees are more likely to attempt suicide than non-adoptees. It might also be upsetting to learn that you had a twin and your birth parents had kept them, as AT did. Having parents with a lower socio-economic status also increases the risk of suicide. AT was therefore more at risk for suicide to start with, although we also know that family support reduces the risk of suicide for people with gender dysphoria.

An interesting aspect of this study is that LT was a “sickly infant” and had hypospadias, a birth defect in the urethra. The Intersex Society of America lists it as an intersex condition. There is no information in the study as to whether or not AT also had hypospadias or any other intersex condition.

Did the hypospadias contribute to LT’s gender dysphoria? Could having a scar on your penis influence feelings about gender identity?

Could the hypospadias be a sign of something else that also caused LT’s gender dysphoria?

According to Wikipedia, the cause of most cases of hypospadias is unknown, but it may be influenced by: having an older mother, the mother taking progesterone during pregnancy, the fetus not producing enough testosterone or nor responding to it, or genetics. It seems reasonable to ask if these factors might also affect gender identity.

In this case, the mother was 40 when the twins were born, which might have been a factor in LT’s hypospadias. We don’t know about any hormonal factors.

We have no way of knowing what caused LT’s hypospadias, but it does raise the question of whether the twins’ issues with gender were caused by a genetic factor or something to do with the prenatal environment or the genital surgery.

I am frustrated by this study. It seems like a good case for a genetic component to gender dysphoria – twins reared apart are a classic test of genetic effects. Unfortunately, since it is based on the account of one twin, the evidence is not as strong. It might be that the twin who lived developed a narrative to make sense of his twin’s tragic suicide.

In addition, the fact that one twin had an intersex condition at birth might be a sign of something unusual in the twin’s prenatal environment.

Mostly, though, you can’t say you have scientific proof that the twins were alike if you only interview one of the pair of twins.

It is so very hard to get good data on gender dysphoria. People with gender dysphoria are extremely rare and twins with gender dsyphoria are even rarer. Add in a much-too-high suicide rate, and you have even less ability to collect data.

Once again, we need more research in this area. As Heylens et. al said in their review of the literature: “detailed registers of GID twins, preferably on MZ twins discordant for GID and DZ twins are needed, to gain more decisive information about the influence of genetic vs. environmental factors in the development of GID.

Original Case Report:

Identical Reared apart Twins Concordant for Transsexuality by Nancy Segal & Milton Diamond, Letter to the Editor, published in: Journal of Clinical and Experimental Medicine, April 2014 Volume 6, Issue 2, Page 74.

*The article refers to the twins with male pronouns. The article does not make it clear what the twins did when they grew up. LT, if you have transitioned and I am using the wrong pronouns, I apologize.

More about twins and gender dysphoria:

My review of “Gender Identity Disorder in Twins: A Review of the Case Report Literature.”

A review of “Gender Identity Disorder in Twins: A Review of the Case Report Literature”

The data on twins suggests that there is a genetic component to gender dysphoria.

It also suggests that other factors are involved in developing gender dysphoria.

Unfortunately, the data is weak because it is mostly made up of case studies.

In addition, the data on identical twins and the data on fraternal twins were collected in different ways.

It is possible that this review overestimates the influence of genes due to the way the data was collected.

I had thought that writing this review would be quick and easy; genes are involved, but they are not the only factor. The truth is that the data is flawed and we don’t have conclusive proof yet. What we do have is a suggestion that genes are involved in gender dysphoria and a need for more research in this area.

Data on twins with gender dysphoria is hard to collect because it is rare. This review is an important one and it shows that there are good reasons to keep looking for possible genetic links to gender dysphoria. It also shows that there are good reasons to look for non-genetic factors that play a role in developing gender dysphoria.

Now you have the summary of the results, back to the study. Why does it mattter if many of the reports on identical twins came from case studies?

Using case studies means that there is a possibility of selection bias.

People may be more likely to publish interesting cases. For example, the review includes one case study where both identical twins had gender dysphoria, but only one had schizophrenia. In another case study both identical twins had anorexia, but only one had gender dysphoria. These cases are interesting, but they may not be typical.

This can become a more serious problem if therapists are more likely to be interested in cases of twins who are both trans. Alternatively, there could be a selection bias in favor of writing about identical twins where only one twin is trans. Some therapists might unconsciously look for cases of twins that fit their own theory about the cause of gender dysphoria. (Read more about case studies and selection bias here.)

The results of this review suggest that there is a selection bias that favors identical twins over fraternal twins. In other words, people write up and publish cases of identical twins more often than fraternal twins.

This is not because trans people don’t have fraternal twins; the studies that reviewed clinic records found 19 sets of fraternal same-sex twins and only 7 sets of identical twins. Only 27% of the twins in this group were identical twins. This is not surprising; fraternal twins are more common than identical twins in the general public.

The other studies, in contrast, reported on 16 sets of identical twins and only 2 sets of fraternal twins. A whopping 89% of the twins in this group were identical twins.

The key to figuring out if gender dysphoria is genetic is to compare identical twins and fraternal twins. If identical twins are more likely to both have gender dysphoria than fraternal twins, you have a good case for a genetic contribution. So if the sets of identical twins are chosen in a different way from the sets of fraternal twins, you have a problem.

In fact, for this study most of the data on identical twins is coming from case reports; there might be a selection bias involved there. Almost all of the data on fraternal twins, however, is coming from comprehensive reviews of clinic records.

Reviews of case studies include a number of other problems.

You can’t be sure people are being diagnosed in the same way; you may not be looking at the same phenomenon. This review looked at people diagnosed by different therapists in at least ten different countries.* The dates of the studies ranged from 1956 to 2011. Some of the twins were children or teens, some were adults.

There may also be cultural or environmental differences that are relevant. For example, one of the case studies is of a pair of identical twins in Iran. Both twins are trans. We know that many people feel pressured to transition in Iran; what if that is a factor in this particular case? What if in another country, only one of the twins would have transitioned?

The era of the study might also affect gender dysphoria. For example, the Belgian clinic noticed that two of the fraternal twins with gender dysphoria they found had been born after in vitro fertilization. If IVF is a factor in gender dysphoria, it will only affect later cases.**

The data in case studies is not uniform; this makes it hard to compare. For example, one study discussed birth weights while another focused on relationships with parents.

This review of studies did include three sets of twins who were found in a method that did not have a selection bias or problems with inconsistent collection of data.

1) Zucker looked at the records of 561 patients who went to a Canadian clinic for gender dysphoria between 1976 and 2011 and found 25 sets of twins. The patients were all under 12 years old.

They found no cases where both twins had gender dysphoria.

2) Heylens and De Cuypere looked at 3 sets of adult twins from the 450 patients who went to a Belgian gender clinic between 1985-2011 plus 3 sets of non-adult twins who went to the Belgian gender clinic for children and teenagers.

They found only one case where both of the twins had gender dysphoria: a set of identical twins who were female-to-male transgender (FtM).

3) Vujovic et al reviewed all the cases of gender dysphoria who were treated at a Serbian clinic between 1987 and 2006. Out of 147 people, one trans man and one trans woman had a fraternal twin. Neither of their twins had gender dysphoria.

If we exclude case studies because of possible bias, we end up with no genetic component to gender dysphoria in trans women. None of the clinics found pairs of male twins who both had gender dysphoria.

The problem with this approach is that identical twins who are both male-to-female transsexuals exist. They just didn’t show up at these three clinics. Presumably, they are very rare.

Using the clinic studies for trans men we would have one set of identical Belgian twins who both had gender dysphoria, and one set of identical Canadian twins who did not. In addition, we would have three sets of fraternal twins where only one twin had gender dysphoria. This is not enough data.

So it makes sense to look at the data from individual case studies; we just need to be cautious about interpreting it. It is possible that it would over or underestimate the genetic component to gender dysphoria.

What was the data, then?

The authors searched the literature and put their data from the three clinics together with data from 17 different case reports and studies.***

They found:

FtMs with identical twins

3 sets of identical twins who both had gender dysphoria (37.5%)

5 sets of identical twins where only one of the twins had gender dysphoria (62.5%)

FtMs with fraternal twins

5 sets of fraternal twins where only one of the twins had gender dysphoria (100%)

MtFs with identical twins

6 sets of identical twins where both twins had gender dysphoria (40%)

9 sets of identical twins where only one twin had gender dysphoria (60%)

MtFs with fraternal twins

16 sets of fraternal twins where only one twin had gender dysphoria (100%)

Based on this data, identical twins with gender dysphoria are more likely than fraternal twins or the general public to have a twin with gender dysphoria. This suggests a genetic component to gender dysphoria.

However, most of the time, only one identical twin has gender dysphoria. This suggests other factors are involved in gender dysphoria.

At this point, we have no idea what the other factors involved might be. The case reports don’t give enough information on the twins to figure it out. The information they give is inconsistent; one study reported on the age of the first period while another talked about whether or not the mother was domineering. In addition, we may be comparing apples and oranges; for example, one study looked at an adult male American Indian in 1976, another looked at 13 year old American females in 1992.

The authors of the review conclude:

“The etiology of GID is a complex process of biopsychosocial components with unexplained interactions. Twin literature on GID supports the contribution of genetic factors to the development of gender identity with a higher tendency in males than in females.****

Since sample size is still limited and genotype studies are lacking, conclusions must be drawn with caution.

Therefore, detailed registers of GID twins, preferably on MZ twins discordant for GID and DZ twins are needed, to gain more decisive information about the influence of genetic vs. environmental factors in the development of GID.

The authors of the study combine the data from studies of MtF and FtM twins for the statistical analysis. This gives them 9 pairs of identical twins where both twins had gender dysphoria (39%) and 14 pairs of identical twins where only one twin had gender dysphoria (61%). This is contrasted with 21 sets of fraternal twins where only one twin had gender dysphoria (100%). The difference is statistically significant.

This might be problematic since the mechanism that causes gender dysphoria in trans women is probably different from the mechanism that causes gender dysphoria in trans men. The genes are also probably different.

On the other hand the question here is whether or not gender dysphoria is inheirited, so perhaps this works.

Another problem is the possibility of selection bias. It looks like people are over-reporting cases involving identical twins. This might affect comparisons between identical twins and fraternal twins.

In addition, the total size of the group used in their statistical analysis is small and includes disparate groups – males and females, adults and children, people in different countries, and people living in different eras.

In the end, we’re left with weak evidence for a genetic component to gender dysphoria. We can’t prove it, but there is an excellent case for doing more studies in this area.

There is also an excellent case for future studies looking at what factors make one identical twin have gender dysphoria and one not. This seems to be the more common outcome than for both twins to have gender dysphoria.*****

Original Review:

Gender Identity Disorder in Twins: A Review of the Case Report Literature by Heylens G, De Cuypere G, Zucker KJ, Schelfaut C, Elaut E, Vanden Bossche H, De Baere E, T’Sjoen G in J Sex Med. 2012 Mar;9(3):751-7.

 

*Authors of the studies were from Belgium, Canada, Germany, Iran, Israel, the Netherlands, Serbia, Switzerland, the United Kingdom, and the United States. In addition, one author seemed to be from Scandinavia, possibly either Norway or Sweden.

**Using IVF means that the parents were infertile. It might be that the parents were older or that they had something wrong with their reproductive systems. It could be that the parent’s age or fertility problems affected the children rather than the IVF procedure.

***In some cases, it is hard to tell from the title if an article was a study or case report or an article on gender dysphoria that includes information on a case. Then again, the sub-title of this study is “A review of the case report literature,” so maybe they were all case reports.

**** I think the idea that there is a higher tendency in males than females is overstated. There were only 8 pairs of identical FtM twins and I doubt the 2.5% difference in the frequency of FtM versus MtF identical twin pairs who both have gender dysphoria is significant.

***** There may be selection bias in the cases of identical twins from the case reports. However, the clinic studies did find six sets of identical twins. In five of these six pairs, only one twin had gender dysphoria. Specifically, they found four pairs of identical male twins where only one twin had gender dysphoria, one pair of identical female twins where only one twin had gender dysphoria, and one pair of identical twins who were both FtM. So it looks like it is more common for only one identical twin to have gender dysphoria.

Emphases added are mine, including in the quote from the original review of the literature.