Study finds epigenetics, not genetics, underlies homosexuality

KNOXVILLE – Epigenetics – how gene expression is regulated by temporary switches, called epi-marks – appears to be a critical and overlooked factor contributing to the long-standing puzzle of why homosexuality occurs.

According to the study, published online today in The Quarterly Review of Biology, sex-specific epi-marks, which normally do not pass between generations and are thus "erased," can lead to homosexuality when they escape erasure and are transmitted from father to daughter or mother to son.

From an evolutionary standpoint, homosexuality is a trait that would not be expected to develop and persist in the face of Darwinian natural selection. Homosexuality is nevertheless common for men and women in most cultures. Previous studies have shown that homosexuality runs in families, leading most researchers to presume a genetic underpinning of sexual preference. However, no major gene for homosexuality has been found despite numerous studies searching for a genetic connection.

In the current study, researchers from the Working Group on Intragenomic Conflict at the National Institute for Mathematical and Biological Synthesis (NIMBioS) integrated evolutionary theory with recent advances in the molecular regulation of gene expression and androgen-dependent sexual development to produce a biological and mathematical model that delineates the role of epigenetics in homosexuality.

Epi-marks constitute an extra layer of information attached to our genes' backbones that regulates their expression. While genes hold the instructions, epi-marks direct how those instructions are carried out – when, where and how much a gene is expressed during development. Epi-marks are usually produced anew each generation, but recent evidence demonstrates that they sometimes carryover between generations and thus can contribute to similarity among relatives, resembling the effect of shared genes.

Sex-specific epi-marks produced in early fetal development protect each sex from the substantial natural variation in testosterone that occurs during later fetal development. Sex-specific epi-marks stop girl fetuses from being masculinized when they experience atypically high testosterone, and vice versa for boy fetuses. Different epi-marks protect different sex-specific traits from being masculinized or feminized – some affect the genitals, others sexual identity, and yet others affect sexual partner preference. However, when these epi-marks are transmitted across generations from fathers to daughters or mothers to sons, they may cause reversed effects, such as the feminization of some traits in sons, such as sexual preference, and similarly a partial masculinization of daughters.

The study solves the evolutionary riddle of homosexuality, finding that "sexually antagonistic" epi-marks, which normally protect parents from natural variation in sex hormone levels during fetal development, sometimes carryover across generations and cause homosexuality in opposite-sex offspring. The mathematical modeling demonstrates that genes coding for these epi-marks can easily spread in the population because they always increase the fitness of the parent but only rarely escape erasure and reduce fitness in offspring.

"Transmission of sexually antagonistic epi-marks between generations is the most plausible evolutionary mechanism of the phenomenon of human homosexuality," said the study's co-author Sergey Gavrilets, NIMBioS' associate director for scientific activities and a professor at the University of Tennessee-Knoxville.

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The paper's other authors are William Rice, a professor at the University of California, Santa Barbara, and Urban Friberg, a professor at Uppsala University in Sweden.

The National Institute for Mathematical and Biological Synthesis (NIMBioS) brings together researchers from around the world to collaborate across disciplinary boundaries to investigate solutions to basic and applied problems in the life sciences. NIMBioS is sponsored by the National Science Foundation, the U.S. Department of Homeland Security, and the U.S. Department of Agriculture with additional support from The University of Tennessee, Knoxville.

Citation: Rice WR, Friberg U, Gavrilets S. Homosexuality as a consequence of epigenetically canalized sexual development. The Quarterly Review of Biology. Published online 11 December 2012.

New Study Shows Structural Factors Play Major Role in Access to HIV Services for Gay Men Worldwide

Global survey finds homophobia, comfort with service provider, and community engagement make significant impact on access to condoms, lubricant, HIV testing, and HIV treatment

OAKLAND, Calif.  -- A large-scale study of gay men and other men who have sex with men (MSM), conducted by the Global Forum on MSM & HIV (MSMGF), indicates that only one third of MSM can easily access condoms, lubricant, HIV testing, and HIV treatment. Combining a multi-lingual online survey and focus group discussions, the study suggests that structural barriers like homophobia play a significant role in blocking access to HIV services for MSM, while greater comfort with health service providers and more community engagement are associated with higher levels of service access.

The MSMGF's study aimed to identify factors that affect access to HIV services for MSM. The online survey conducted earlier this year included 5779 men from 165 countries.  In addition, the MSMGF collaborated with African Men for Sexual Health and Rights (AMSHeR) to conduct focus group discussions with 71 MSM across five cities in South Africa, Kenya, and Nigeria.

Of men who participated in the online survey, only 35% reported that condoms were easily accessible, 21% reported easy access to lubricant, 36% reported easy access to HIV testing, and 42% reported easy access to HIV treatment. Levels of access differed by country income level, with reduced access to services more commonly reported in lower income countries.

"Such poor levels of access at the global level are unacceptable," said Dr. George Ayala, Executive Director of the MSMGF. "The differences in access by country income are especially important to note as the Global Fund moves into a new funding model where countries are grouped into bands by income level. Even in upper middle income countries, MSM still have extremely low access to services. Without targeted funding to MSM and other key populations, the new funding model may continue to deteriorate levels of access for the groups most affected by HIV."

The MSMGF research team also conducted analyses to identify barriers (factors associated with lower access) and facilitators (factors associated with higher access) that impact the ability of MSM to obtain condoms, lubricant, HIV testing, and HIV treatment.

Adjusting for country income, greater access to condoms, lubricants, and HIV testing were associated with less homophobia, greater comfort with health service providers, and more community engagement. Among participants living with HIV, higher access to HIV treatment was associated with less homophobia and greater comfort with health service providers.  Greater access to lubricants and greater access to HIV testing were also associated with less outness (the degree to which others know of one's sexual orientation) and fewer negative consequences as a result of being out, respectively.

"As we collectively forge ahead into the new territory of treatment-based prevention, it is clear that many of the old challenges remain," said Noah Metheny, Director of Policy at the MSMGF. "Addressing structural barriers remains essential to realizing the potential of HIV interventions for MSM, and it becomes more important with each new prevention and treatment option that is made available. Investments in the development of new interventions must be accompanied by efforts to increase access."

The quantitative data from the online survey was supplemented with qualitative data from focus group discussions, helping to place barriers and facilitators in the broader context of the sexual health and lived experiences of MSM. Focus group discussion participants identified barriers and facilitators that were highly consistent with those found in the online survey, and many participants explained the ways that structural barriers at the policy, cultural, and institutional levels cascade down through the community and individual levels to block access to services for MSM.

Focus group discussion participants described how structural barriers like stigma, discrimination, and criminalization force MSM to hide their sexual behavior from health care providers, employers, landlords, teachers, and family members in order to protect themselves and maintain a minimum livelihood. The inability of MSM to reveal their sexual behavior to health service providers was linked to misdiagnosis, delayed diagnosis, and delayed treatment, leading to poor health prognosis and higher risk of transmitting HIV and other sexually transmitted infections to partners.

Conversely, focus group discussion participants explained that the negative consequences of structural barriers were moderated by the existence of safe spaces to meet other MSM, safe spaces to receive services, access to competent mental health care, and access to comprehensive health care. Participants described MSM-led community based organizations as safe spaces where they could celebrate their true selves, receive respectful and knowledgeable health care, and in some cases receive mental health services.

"The study's findings underscore the urgent need to improve access to essential HIV services for gay men and other MSM worldwide," said Dr. Ayala. "Interventions must both disrupt the negative effects of barriers and bolster the protective effects of facilitators. Study participants clearly indicated that community engagement and community-based organizations are central to moderating barriers and promoting service access. Successfully addressing HIV among MSM will require a real effort to address structural barriers, and the findings from this study suggest that investing in MSM-led community-based organizations may be the best way to do that."

Entitled, "Access to HIV Prevention and Treatment for Men Who Have Sex with Men: Findings from the 2012 Global Men's Health and Rights Study (GMHR)," the full report can be found on the MSMGF's website at: http://www.msmgf.org/files/msmgf//documents/GMHR_2012.pdf