Abstract
This study was conducted to clarify the genetic and environmental factors for some problem behaviors during sleep in childhood, namely sleep talking, half-sleeping, night terrors and nocturnal enuresis. The subjects were 881 pairs of twins, consisting of 609 monozygotic (279 male-male, 330 female-female) and 272 dizygotic (86 male-male, 84 female-female, 102 opposite-sexed). They were all applicants to the junior high school affiliated with Tokyo University from 1981 to 1998. The twins' mothers had previously completed a medical questionnaire and had been interviewed by three to five interviewers. With regard to the above mentioned four traits, they selected one answer from the choices ‘often’, ‘sometimes’ ‘never’ and ‘unknown’ for each twin. The interviewer checked the answers and, where necessary, explained the meaning of any terms such as “night terrors”. Genetic analysis was performed as follows. First the answers were summarized in the form of a 2×2 contingency table; ‘often’ and ‘sometimes’ were included in one category. Then, tetrachoric correlations of the contingency table were calculated according to zygosity using the program package PRELIS2. Furthermore, covariance structure analysis was performed for several genetic models using the program package LISREL8. The results were as follows. Univariate genetic analysis showed that all four traits were under genetic control. Sleep talking, half-sleeping and night terrors were under strong or moderate genetic control. As to nocturnal enuresis, the genetic effect was moderate and shared environmental factors played an important role. Sex difference was observed in the case of half-sleeping and enuresis. Moreover these traits tended to occur together, and sleep talking, half-sleeping and night terrors shared common genetic and environmental factors in addition to specific genetic and environmental factors.
