BACKGROUND: Familial clustering has been reported for urinary incontinence (stress and urge), but different etiologies for the two types of incontinence have been suggested.

OBJECTIVE: The aim of this study was to estimate the relative influence of genetic and environmental factors on stress, urge, and mixed incontinence among elderly and middle-aged women.

METHODS: This is a population-based classical twin study of 1168 female twin pairs [548 monozygotic (MZ) and 620 dizygotic (DZ)] from a middle-aged (46-68 years) and an old (70-94 years) cohort identified in the Danish Twin Registry. Urinary incontinence was assessed with the help of two validated questions identifying stress and urge incontinence in interviews.

RESULTS: For urge incontinence, the tetrachoric correlation was significantly higher for MZ twins, compared to that for DZ twin pairs in both middle-aged [0.51 (95% CI: 0.26-0.71) versus -0.22 (95% CI: -0.59-0.18)] and elderly [0.50 (95% CI: 0.27-0.68) versus 0.28 (95% CI: 0.02-0.42)], indicating genetic effects. The heritability of urge incontinence was 42% (95% CI: 16-63%) among middle-aged women and 49% (95% CI: 29-65%) among the elderly. Moreover, mixed incontinence had a substantial genetic component. The role of genetic factors was less clear in stress incontinence.

CONCLUSIONS: Genetic factors play a substantial role in the development of urge and mixed incontinence, whereas the role of genetic factors in stress incontinence is less prominent.