BERKELEY, CA (UroToday Inc.) - The etiology of urinary incontinence is not known. Most would agree that there are likely to be both environmental as well as genetic factors that contribute to the development of female urinary incontinence. Gitte Rohr and colleagues from the University of Southern Denmark in Odense, Denmark used the Danish Twin Registry to estimate the relative influences of genetic and environmental factors on stress, urge, and mixed incontinence in middle-aged and elderly women.

Their findings were published in the October 2004 edition of Acta Obstetricia et Gynecologica Scandinavica. In their study, 1168 female twin pairs, both monozygotic (MZ) and dizygotic (DZ), from the Danish Twin Registry completed two validated questions to identify stress and urge incontinence. If both stress and urge incontinence were identified, then the subject was classified as having mixed incontinence. They were also categorized as middle-aged, 46-68 years old, and old, 70-94 years old. They looked at probandwise concordance, defined as the proportion of affected twin partners of probands, and tetrachoric correlation, in which a higher correlation rate in MZ twins suggests a strong influence by genetic factors. They also estimated heritability by using biometric models.

Overall 27% met the criteria for any urinary incontinence. The probandwise concordance rates and tetrachoric correlations for urge incontinence and mixed incontinence were higher for MZ, compared to DZ twins, thereby suggesting the influence of genetic factors. There was no significant concordance or correlation with stress incontinence. Substantial heritability was seen in urge incontinence with 42% in middle-aged and 49% in elderly twins.

In conclusion, it appears that genetics factors are quite influential in the developmental of urge and mixed urinary incontinence, while stress urinary incontinence may be more related to environmental factors.

Acta Obstet Gynecol Scand 2004; 83: 978-982