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The Keio Twin Research Center (KoTReC) was established in 2009 at Keio University to combine two longitudinal cohort projects — the Keio Twin Study (KTS) for adolescence and adulthood and the Tokyo Twin Cohort Project (ToTCoP) for infancy and childhood. KoTReC also conducted a two-time panel study of self-control and psychopathology in twin adolescence in 2012 and 2013 and three independent anonymous cross-sectional twin surveys (ToTcross) before 2012 — the ToTCross, the Junior and Senior High School Survey and the High School Survey. This article introduces the recent research designs of KoTReC and its publications.
The Keio Twin Research Center has conducted two longitudinal twin cohort projects and has collected three independent and anonymous twin data sets for studies of phenotypes related to psychological, socio-economic, and mental health factors. The Keio Twin Study has examined adolescent and adult cohorts, with a total of over 2,400 pairs of twins and their parents. DNA samples are available for approximately 600 of these twin pairs. The Tokyo Twin Cohort Project has followed a total of 1,600 twin pairs from infancy to early childhood. The large-scale cross-sectional twin study (CROSS) has collected data from over 4,000 twin pairs, from 3 to 26 years of age, and from two high school twin cohorts containing a total of 1,000 pairs of twins. These data sets of anonymous twin studies have mainly targeted academic performance, attitude, and social environment. The present article introduces the research designs and major findings of our center, such as genetic structures of cognitive abilities, personality traits, and academic performances, developmental effects of genes and environment on attitude, socio-cognitive ability and parenting, genes x environment interaction on attitude and conduct problem, and statistical methodological challenges and so on. We discuss the challenges in conducting twin research in Japan.
This study examined the link between sibling relationships and children's social adjustment by comparing twin siblings and siblings with different ages (singleton siblings), and clarified the role of reciprocity in sibling relationships on children's social development. Mothers of 58 monozygotic twin pairs, 48 dizygotic twin pairs, and 86 singleton sibling pairs reported their children's sibling relationships and social adjustment. This study showed that the effects of sibling relationships on the prosocial behaviors and conduct problems of each child are stronger for twins than for singleton siblings. Moreover, positivity toward one's sibling increased peer problems only among monozygotic twins. The opposite tendency was present among dizygotic twins and singleton siblings. This study suggests the importance for children's social development of having many interactions with siblings and establishing reciprocity in sibling relationships. Moreover, our results suggest that the quality of sibling relationships among monozygotic twins may be different from those among dizygotic twins and singleton siblings.
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