from What do clinical studies say?
By: James E. Phelan, LCSW, BCD
NARTH Scientific Advisory Committee
Zietsch, Verweij, Bailey, Wright, and Martin (2009) identify themselves as from the Genetic Epidemiology department of The Queensland Institute of Medical Research in Australia, although J. M. Bailey is from Northwestern University in the United States, and no stranger to the study of sexual orientation and genetics. The authors note that from studying the literature, homosexuals and bisexuals on average, are at greater risk for psychiatric problems than heterosexuals.
The current study was done in an effort to find out what mechanisms (e.g. "minority stress," environmental factors, and/or genetic factors) might likely elevate the psychiatric vulnerability of nonheterosexuals. In conducting their literature review, some support was found for a "minority stress" hypothesis, however such support was weakened by the fact that the relationship between sexual orientation and mental health is strong even in socially liberal countries, such as the Netherlands.
To test what mechanism(s) might likely contribute to the psychiatric vulnerabilities of nonheterosexuals, standardized instruments measuring neuroticism and psychoticism were used as estimates of these two broad types of psychiatric vulnerability. Researchers used a classical twin design, where variance in traits, and covariance between them were partitioned into genetic and environmental sources. The sample compared heterosexuals with nonheterosexuals in a community-based (Australian) sample of identical (monozygotic; MZ) and nonidentical (dizygotic; DZ) twins for a total sample size of 4904. These were the same subjects, recruited in 1992, and previously used in a study by Bailey, Dunne, and Martin (2000) (B. P. Zietsch, personal communication, July 23, 2009). Bailey and Martin also contributed to the current study.
The researchers found that scores on both Neuroticism and Psychoticism scales (e.g. Eysenck Personality Questionnaire [EPQ-R]) were significantly elevated in nonheterosexuals compared with heterosexuals, indicating greater vulnerability to neurotic and psychotic disorders, respectively. Secondly, researchers claim that analyses with the genetically informative sample revealed significant genetic correlations (e.g. age, sex, zygosity) between sexual orientation and both Neuroticism and Psychoticism, but corresponding environmental correlations were not significant. This suggested to the authors that some of the genetic variation underlying sexual orientation also affects levels of Neuroticism and Psychoticism. Low opposite-sex pair (genetic) correlation in sexual orientation suggested that "different factors may influence sexual orientation in males and females."
Zietsch, et al., conjecture that it was unlikely that an environmental factor, such as childhood sexual abuse, drives the elevated psychiatric risk in nonheterosexuals by predisposing them to both nonheterosexuality and elevated psychiatric vulnerability. However, unknown non-genetic (environmental) factors not shared between twin pairs, along with measurement error, accounted for over 50% of the variance in sexual orientation.
The authors suggest that these factors could include prenatal effects, idiosyncratic experiences, unequal parental treatment, interactions with siblings, or influences outside the family (e.g., teachers and peers). They go on to suggest that, whatever the specific environmental factors were, they seemed not to overlap much at the population level with the environmental factors underlying Neuroticism or Psychoticism levels, given the very low environmental correlations found. The authors admit that this does not discount the possibility that, in individual cases, an environmental influence during development could lead to a nonheterosexual orientation as well as psychiatric vulnerability.
The authors -- unable to give a definitive answer to whether or not homosexuality is genetically caused -- made a plea that further research be conducted, and stated that if there is a biological correlate of both sexual orientation and psychiatric vulnerability, it might be more clearly observed in brain imaging research.
The authors state clearly,
The finding in our data of genetic correlations between sexual orientation and psychiatric vulnerability should be interpreted with caution, as it does not necessitate that pleiotropic genetic factors are at work. Other causal relationships could also manifest as genetic correlation between sexual orientation and psychiatric vulnerability. It is likely that there are several contributing factors to the elevated psychiatric risk in nonheterosexuals, genetics being one of these factors.
"Caution" indeed. Another key word they used is "likely," but in reality, their estimate of "likelihood" is not definitive. Even those correlates that were discovered (e.g. gender nonconformity), do not explain a genetic basis in totality, as environmental factors also have been observed in some cases (Zucker & Bradley, 1995).
If noncommon environmental factors accounted for more than 50%, and the genetic factors were less, than this in itself shows that the genetic contribution was not 100% and therefore cannot give a "definitive yes" answer to the question "Are people born gay?" Erratic, noncommon (i.e., idiosyncratic) environmental factors are predominant, and this finding is significant.
It should also be pointed out that the finding of elevated psychoticism done in such a standard way is almost unique in the modern literature. Although historically it has been clear that some elements of psychoticism have been associated with various subpopulations of homosexually oriented people, older studies lack the rigor of the current paper. While it is more common to find older papers reporting neurotic aspects of homosexually oriented people, this current paper uses a more general client population and is better controlled methodologically.
The NARTH Journal of Human Sexuality (2009), explored the extensive evidence for increased neuroticism among homosexually oriented people. The Zietsch et al. paper is important in that it adds psychoticism as well as neuroticism (in the particular meaning given both terms by the EPQ-R and others) to the surprisingly long list of ills experienced by homosexually oriented people to a significantly greater extent than heterosexuals.
Bailey, J. M., Dunne, M. P., & Martin, N. (2000). Genetic and environmental influences on sexual orientation and its correlates in an Australian twin sample. Journal of Personality and Social Psychology, 78(3), 524-536.
National Association for Research and Therapy of Homosexuality (NARTH) Scientific Advisory Committee (2009). What research shows: NARTH's response to the American Psychological Association's (APA) claims on homosexuality. Journal of Human Sexuality, 1, 1-128.
Zietsch, B. P, Verweij, K. J. H., Bailey, J. M., Wright, M. J., & Martin, N. G. (2009). Sexual orientation and psychiatric vulnerability: A twin study of neuroticism and psychoticism. Archives of Sexual Behavior, (published online: 09 July 2009, Springer Publications)
Zucker, K. J., & Bradley, S. J. (1995). Gender identity disorder and psychosexual problems in children and adolescents. New York: The Guilford Press.