Multivariate genetic analysis of chronic pelvic pain and associated phenotypes.

Chronic pelvic pain (CPP) is a common condition in women that is difficult to diagnose. Although heritability estimates have been published for some conditions potentially underlying pelvic pain, the heritability of CPP itself has never been investigated. Using data from 623 MZ and 377 DZ female twin pairs aged 29-50 from an Australian twin cohort, we found an increased CPP concordance among MZs compared to DZs, with tetrachoric correlations of 0.43 (95% CI: 0.26-0.58) and 0.11 (95% CI: -0.16-0.38), respectively. This corresponded to a heritability of 0.41 (95% CI: 0.25-0.56). Lack of correlations with environmental indicators suggested that violation of the equal environments assumption was not responsible for this effect. Multivariate Cholesky decomposition models incorporating CPP and significantly correlated phenotypes showed that the entire CPP heritability could be explained by genetic variance underlying endometriosis (38%), dysmenorrhoea (23%), fibroids (24%), and somatic distress (15%), the latter a possible indicator of increased nociception. CPP itself is unlikely to be a useful independent phenotype to conduct genetic aetiological studies; contributing conditions such as endometriosis and variation in nociception are likely to provide more useful phenotypes.