Bladder neck mobility is a heritable trait.

OBJECTIVE Congenital connective tissue dysfunction may partly be responsible for female pelvic organ prolapse and urinary incontinence. We undertook a heritability study to determine whether mobility of the bladder neck, one of the main determinants of stress urinary incontinence, is genetically influenced. DESIGN Heritability study using a twin model and structural equation modelling. SETTING Queensland Institute of Medical Research, Brisbane, Australia. POPULATION One hundred and seventy-eight nulliparous Caucasian female twins and their sisters (46 monozygotic pairs, 24 dizygotic pairs and 38 sisters) aged 18-24 years. METHODS We performed translabial ultrasound, supine and after bladder emptying, for pelvic organ mobility. Urethral rotation and bladder neck descent were calculated using the best of three effective Valsalva manoeuvres. MAIN OUTCOME MEASURES Bladder and urethral mobility on Valsalva assessed by urethral rotation, vertical and oblique bladder neck descent. RESULTS Genetic modelling indicated that additive genes accounted for up to 59% of the variance for bladder neck descent. All remaining variance appeared due to environmental influences unique to the individual, including measurement error. CONCLUSION A significant genetic contribution to the phenotype of bladder neck mobility appears likely.