Abstract
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.