Bladder pain syndrome/interstitial cystitis in twin sisters

We determined the genetic contribution of and associated factors for bladder pain syndrome using an identical twin model.

Multiple questionnaires were administered to adult identical twin sister pairs. The O'Leary-Sant Interstitial Cystitis Symptom and Problem Index was administered to identify individuals at risk for bladder pain syndrome. Potential associated factors were modeled against the bladder pain syndrome score with the twin pair as a random effect of the factor on the bladder pain syndrome score. Variables that showed a significant relationship with the bladder pain syndrome score were entered into a multivariable model.

In this study 246 identical twin sister pairs (total 492) participated with a mean age (± SD) of 40.3 ± 17 years. Of these women 45 (9%) were identified as having a moderate or high risk of bladder pain syndrome (index score greater than 13). There were 5 twin sets (2%) in which both twins met the criteria. Correlation of bladder pain syndrome scores within twin pairs was estimated at 0.35, suggesting a genetic contribution to bladder pain syndrome. Multivariable analysis revealed that increasing age (estimate 0.46 [95% CI 0.2, 0.7]), irritable bowel syndrome (1.8 [0.6, 3.7]), physical abuse (2.5 [0.5, 4.1]), frequent headaches (1.6 [0.6, 2.8]), multiple drug allergies (1.5 [0.5, 2.7]) and number of self-reported urinary tract infections in the last year (8.2 [4.7, 10.9]) were significantly associated with bladder pain syndrome.

Bladder pain syndrome scores within twin pairs were moderately correlated, implying some genetic component. Increasing age, irritable bowel syndrome, frequent headaches, drug allergies, self-reported urinary tract infections and physical abuse were factors associated with higher bladder pain syndrome scores.