The transmission of primary nocturnal enuresis (PNE) in relatives of PNE and control probands, with and without ADHD, was examined at the University of California at Los Angeles. Among 126 male probands with and without PNE and ADHD, ages 6-12 yrs, and 338 of their first-degree relatives (237 parents and 101 siblings), the rates of enuresis in parents of enuretic children (40%) were significantly higher than in parents of non-enuretic control children (6%), regardless of the co-morbid ADHD of the proband. Of the PNE probands 65% had at least one affected parent, and of these families, 24% had an affected sibling. The rates of PNE between parents or siblings in the PNE and PNE + ADHD groups were similar, both groups having significantly elevated rates of PNE in their relatives. In the ADHD only group, there was no familial clustering of PNE. The rate of PNE in first-degree relatives is independent of ADHD in the proband. ADHD and PNE are transmitted independently. 
COMMENT. The familial nature of nocturnal enuresis is suggested by family studies, twin studies, and a high rate of positive family histories in case studies. The risk of PNE to parents is 6.7-fold, and the risk to siblings 3.6-fold. Rates of enuresis in individuals with ADHD range from 20-30%, compared to 10% in the average population of 7 yr old children. In both conditions, boys are affected more frequently than girls. The frequency of ADHD is increased in PNE children compared to non-PNE controls. The present study suggests that the association of PNE and ADHD is not due to a shared genetic basis.
Factors in etiology of PNE other than genetic transmission are also considered in a commentary by Jarvelin M-R . These include delayed maturation of the nervous system, disturbed arginine-vasopressin secretion, prenatal and birth-related factors, neurobehavioral disorders, and psychosocial factors. Many of these factors also apply to the presumed etiology of ADHD.