A discordant monozygotic twin approach to testing environmental influences on sexual dysfunction in women

The present study explored the causal role played by putative environmental factors on variation in female sexual dysfunction (FSD) by investigating FSD discordant monozygotic (MZ) twins, which permits a control over genetic confounders. In a population-based sample of female twins aged 25-69 years (M = 55 years), MZ twins discordant for recent and lifelong FSD were selected. Sample sizes varied depending on the specific sexual problem (N = 33-90 pairs). The Female Sexual Function Index (FSFI) score was used to discriminate cases from controls. Once genetic factors were controlled for, relationship satisfaction emerged as the strongest independent predictor for recent and lifelong FSD, being associated with FSFI dimensions measuring desire, arousal, and lubrication problems. The association with orgasm problems was especially strong (OR 7.1, 95% CI: 1.9-25.3) as was the association with sexual dissatisfaction (OR 5.1, 95% CI: 2.1-12.1). Furthermore, obsessive-compulsive symptomatology was weakly associated with desire problems (OR 1.5, 95% CI: 1.4-1.8) and anxiety-sensitivity with orgasm problems (OR 1.1, 95% CI: 0.9-1.3). Negligible effects were found for personality factors and small effects for self-reported abusive experiences. These data indicate, for the first time, that in women at identical genetic risk, relationship factors play a key role in the development of sexual problems. These findings require replication in prospective designs which can provide additional powerful tests of the direction of causality between interpersonal factors and later sexual dysfunction.