W8. HERITABILITY OF ACCELEROMETRY-DERIVED FEATURES OF PHYSICAL ACTIVITY, SLEEP AND CIRCADIAN RHYTHMICITY AND THEIR JOINT INFLUENCES IN YOUNG PEOPLE

Background Dysregulation of motor activity and sleep are key components of several mental disorders, particularly mood disorders and attention deficit hyperactivity disorder (ADHD). There is growing evidence that profiles of 24-hour activity patterns may discriminate subgroups of mood disorders in adults. However, there is limited information on activity profiles in youth that may identify differential risk for psychopathology across development. The aims of this work are: (1) to examine the familial and genetic influences on 24-hour patterns of objectively-assessed activity in young people based on genetically informative samples; and (2) to identify age, sex, and contextual influences on heritability; and (3) to evaluate whether Polygenic Scores (PGS) for sleep, activity, mood, and attention are related to empirically derived estimates of these domains. Methods Samples include two studies of youth from genetically informative study designs including families and twins. Family study data included youth ages 10-25 from the National Institute of Mental Health (NIMH) Family Study of Affective Spectrum Disorders (n=154). Twin study data included 495 youth ages 9-17 from the Brisbane Adolescent Twin Study (BATS) and the Queensland Twin Adolescent Brain (QTAB) project (N=93 monozygotic (MZ); 117 dizygotic (DZ) twin pairs, and 75 unmatched twins). Accelerometry was assessed with the GeneActiv device for two weeks as part of the Motor Activity Research Consortium for Health (mMARCH) collaborative study. Polygenic heritability estimates (adjusted for age and sex) were derived from the Sequential Oligogenic Linkage Analysis Routines (SOLAR) software package for the features of the three domains of physical activity, sleep, and circadian rhythmicity. Components of variance for the twin samples were further estimated with Open MX in R. Associations between heritable accelerometry features with PGS for a range of related domains including sleep, activity, ADHD, depression, and anxiety were also examined. Results Heritability estimates of specific features of sleep, activity, and circadian rhythmicity range from 0.44 to 0.87 and were highly significant in both the twin and family studies, with an increase in heritability with increasing age. Heritability estimates of the variability of many salient features was greater than averages (0.56-0.89), suggesting that heritability of the dynamics of these domains may supersede that of the actual levels of sleep and activity. Strong environmental influences suggested by weekday-weekend differences also highlight the importance of contextual factors in examining these systems. Several of the ADHD and sleep PGS were associated with the circadian rhythmicity and sleep features in both the twin and family data. Discussion The increase in the influence of genetic factors for sleep, physical activity, and circadian rhythms across adolescent development has important implications for prevention and intervention. The high heritability levels for provide important indices of the well-articulated genetic pathways underlying circadian rhythms that should be further explored. Pronounced weekend-weekday differences also indicate the importance of contextual factors involved in these systems. The associations of accelerometry domains with PGS for multiple mental and physical conditions highlight the broad impact of homeostatic regulatory systems on health.