Nocturnal enuresis in a nationwide twin cohort.

We studied the occurrence of nocturnal enuresis (bedwetting) after the age of 4 years, using a questionnaire in a well-defined population, the Finnish Twin Cohort, which consists of 11,220 subjects aged 33-60 years, including 1298 monozygotic and 2419 dizygotic twin pairs. Structural equation modeling techniques were used to estimate variance components to compare different genetic models. Females reported enuresis in childhood "often" in 3.4% (males in 4.0%) and "sometimes" in 5.7% (8.0%). As adults, females had experienced enuresis "weekly" in 0.3% (males in 0.2%) and "monthly" in 0.07% (0.1%). Those who had experienced enuresis in childhood had had "at least sometimes" enuresis as adults in 5.4% of males and in 5.5% of females. Among those who reported they never had experienced enuresis as adults, 70.8% of males and in 77.9% of females had never experienced enuresis in childhood. For enuresis in childhood, the probandwise concordance rate was 0.43 for monozygotic and 0.19 for dizygotic pairs, and in adults 0.25 and 0, respectively. The proportion of total phenotypic variance attributed to genetic influences (due to dominance) was 67% in males (95% confidence interval 57-76%) and 70% in females (61-78%) in childhood enuresis. In conclusion, nocturnal enuresis is common in childhood and rare in adulthood. Our results confirm the central role of genetic liability in enuresis.