Compared with heterosexual persons, non-heterosexual persons have worse mental health. Sexual Minority Stress Theory (SMST) explains the disparity as resulting from stigma and discrimination. To the extent that heterosexual genetic relatives reared with non-heterosexual persons also have worse mental health, SMST is falsified. We conducted a systematic meta-analysis of studies containing family-genetic comparison data to interrogate the empirical support for SMST.

We systematically identified 17 empirical studies in which twins or non-twin siblings reported on both their sexual orientation and their mental health. Subsequently, we conducted a multilevel meta-analysis, focusing on the degree to which any sexual orientation disparity in mental health diminished with genetic relatedness.

Most of the mental health disparities between non-heterosexual and heterosexual persons were eliminated after controlling for family-genetic factors.

The mental health disparity between non-heterosexual and heterosexual persons is reduced by up to two-thirds once familial background factors are accounted for by comparing monozygotic twins discordant for sexual orientation. This suggests that shared familial causes, and not minority stress, are the most important causes of mental health disparities in non-heterosexual persons.

Lesbian, bisexual, or gay individuals (LBGs) have an increased risk for mental health problems compared to heterosexuals, but this association has sparsely been investigated for psychotic disorders. The aim of this study was: (1) to examine whether LBG sexual orientation is more prevalent in individuals with a non-affective psychotic disorder (NAPD) than in people without a psychotic disorder; and if so, (2) to explore possible mediating pathways.

Sexual orientation was assessed in the 6-year follow-up assessment of the Dutch Genetic Risk and Outcome of Psychosis study (GROUP), a case–control study with 1547 participants (582 patients with psychotic disorder, 604 siblings, and 361 controls). Binary logistic regression analyses were used to calculate the risk of patients with a psychotic disorder being LBG, compared to siblings and controls. Perceived discrimination, history of bullying, childhood trauma (CT), and sexual identity disclosure were investigated as potential mediating variables.

The proportion of individuals with LBG orientation was 6.8% in patients (n = 40), 4.3% in siblings (n = 26), and 2.5% in controls (n = 10). The age- and gender-adjusted odds ratio of LBG for patients was 1.57 (95% CI 1.08–2.27; p = 0.019), compared to siblings and controls. Discrimination, bullying, and CT all partially mediated this association.

Adverse social experiences related to sexual minority status may increase the risk for NAPD. Sexual identity, behavior, and difficulties need more attention in everyday clinical practice.