OBJECTIVES: To determine the relative contributions of genetic and environmental factors on daytime and nighttime continuous sleep duration at 6, 18, 30, and 48 months of age, and to identify different subgroups of children who followed different daytime and nighttime sleep duration trajectories and to investigate their etiology. METHODS: The current study included 995 twins (405 monozygotic and 586 dizygotic) of the Quebec Newborn Twin Study recruited from the birth records of the Quebec Statistics Institute. Daytime and nighttime sleep was assessed through maternal reports at 6, 18, 30, and 48 months of age. A semiparametric modeling strategy was used to estimate daytime and nighttime sleep duration trajectories. Quantitative genetic models were used to examine to what extent genetic and environmental factors influenced daytime and nighttime continuous sleep duration. RESULTS: Genetic modeling analyses revealed environmental influences for all daytime sleep duration trajectories. In contrast, strong genetic influences were found for consolidated nighttime sleep duration (except at 18 months and for the short-increasing sleep duration trajectory). CONCLUSIONS: This is the first indication that early childhood daytime sleep duration may be driven by environmental settings, whereas the variance in consolidated nighttime sleep duration is largely influenced by genetic factors with a critical environmental time-window influence at ∼18 months.
OBJECTIVES: Our objectives were to investigate the developmental trajectories of nighttime sleep duration and hyperactivity over the preschool years and to identify the risk factors associated with short nighttime sleep duration and high hyperactivity scores. DESIGN, SETTING, AND PARTICIPANTS: Nighttime sleep duration and hyperactivity were measured yearly by questionnaires administered to mothers of 2057 children from age 1.5 to 5 years. Developmental trajectories of nighttime sleep duration and hyperactivity throughout early childhood were analyzed to determine interassociations. A multinomial logistic regression was performed to determine which factors among selected child, maternal, and family characteristics and parental practices surrounding sleep periods in early childhood were associated with short nighttime sleep duration and high hyperactivity scores. RESULTS: The trajectories of nighttime sleep duration and hyperactivity were significantly associated. The odds ratio (OR) of reporting short nighttime sleep duration was 5.1 for highly hyperactive children (confidence interval [CI]: 3.2–7.9), whereas the OR of reporting high hyperactivity scores was 4.2 for persistently short sleepers (CI: 2.7–6.6). The risk factors for reporting short nighttime sleep duration and high hyperactivity scores were (1) being a boy, (2) having insufficient household income, (3) having a mother with a low education, and (4) being comforted outside the bed after a nocturnal awakening at 1.5 years of age. CONCLUSIONS: The risk of short nighttime sleep duration in highly hyperactive children is greater than the risk of high hyperactivity scores in short sleepers. Preventive interventions that target boys living in adverse familial conditions could be used to address these concomitant behavioral problems.
OBJECTIVE. There is growing evidence that genetic factors are involved in the occurrence of sleep terrors. Twin studies provide invaluable information regarding genetic and environmental factors that can affect the manifestation of the disease; however, most previous twin studies on sleep terrors were performed retrospectively or with a sample that was too small to yield conclusive results. The aim of this large prospective study was to clarify the genetic and environmental contributions to sleep terrors in childhood. METHODS. In all, 390 pairs of monozygotic and dizygotic twins were recruited at birth for a longitudinal study. The prevalence and frequency of sleep terrors were assessed at 18 and 30 months of age with a questionnaire administered to the biological mother of the twins. Zygosity was determined by a questionnaire and genotyping. The prevalence and polychoric correlation for each type of twins were calculated. Structural-equation modeling was used to determine the proportion of variance attributable to additive genetic, shared, and nonshared environmental factors. RESULTS. The prevalence of sleep terrors was 36.9% at 18 months and 19.7% at 30 months; 49% of affected children were boys, and 51% were girls. At 18 months, the polychoric correlations were 0.63 for monozygotic and 0.36 for the dizygotic twins. These were 0.68 (monozygotic) and 0.24 (dizygotic) at 30 months. Our model-fitting analysis showed that sleep terrors were explained by a 2-component model at 18 months (43.7% additive genetic effects and 56.3% nonshared environment) and at 30 months (41.5% additive genetic effects and 58.5% nonshared environment). CONCLUSIONS. These results strongly support the heritability of sleep terrors. There also seems to be continuity in genetic effects with the persistence of sleep-terror symptoms.
OBJECTIVES. Our aim for this study was to determine the prevalence of dyssomnias and various parasomnias in early childhood and to describe their temporal evolution, gender differences, and correlates. METHODS. This research is part of a longitudinal study of child development. A randomized, 3-level, stratified survey design was used to study a representative sample of infants who were born in 1997–1998 in the province of Quebec (Canada). When the children were 2.5 years of age, 1997 families agreed to be interviewed. The presence of dyssomnias or parasomnias was obtained from a self-administered questionnaire that was completed by the mother at each round of measures. RESULTS. The percentage of children with frequent night wakings decreased steadily from 36.3% at age 2.5 to 13.2% at age 6. Similarly, the percentage of children who had difficulty falling asleep at night decreased significantly from 16.0% at ages 3.5 and 4 to 10% at age 5 and to 7.4% at age 6. The overall prevalence of each parasomnia for the period studied was as follows: somnambulism, 14.5%; sleep terrors, 39.8%; somniloquy, 84.4%; enuresis, 25.0%; bruxism, 45.6%; and rhythmic movements, 9.2%. Persistent somnambulism at age 6 was significantly correlated with sleep terrors and somniloquy. Persistent sleep terrors at age 6 were also correlated with somniloquy. Finally, persistent sleep terrors at age 6 were correlated with frequent night wakings. Separation anxiety was associated with persistent night wakings and with somnambulism, bruxism, sleep terrors, and somniloquy. CONCLUSIONS. There is a high prevalence of night wakings and sleep-onset difficulties in preschool children. Parasomnias are highly prevalent in early childhood and are associated with separation anxiety. However, they have little impact on sleep duration.