Registry of Adolescent and Young Adult Twins in the Tokyo Area

Abstract

Since established in 1998, the Keio Twin Project (KTP) has been dedicated to investigating genetic and environmental sources contributing to human psychological traits in adolescence and young adulthood. A population-based twin registry was constructed by the KTP through the use of official residential records in the Tokyo area, and to date requests to participate in our research have generated 1040 pairs of twins and triplets of age 14 to 30, forming one of the largest twin registries in Asia. Our comprehensive datasets, obtained through questionnaires, performance tests, and physical measurements, cover a wide range of human traits: personality, psychiatry, mental health, sociality, cognition, and physical index. Demographic variables and environment of upbringing are also sought by twins and by some parents. This extensive information allows us to clarify the genetic and environmental overlap across multiple traits as well as specificities unique to single traits. Adding an evolutionary psychology perspective to the behavior genetics framework is currently being attempted in order to develop a grand theory of human genetics.

The Second to Fourth Digit Ratio (2D:4D) in a Japanese Twin Sample: Heritability, Prenatal Hormone Transfer, and Association with Sexual Orientation

“…Of the 5,217 pairs of twins to whom we sent letters, 2,073 twin individuals agreed to participate in our research. The registrants were all native Japanese and the participation rate was 20% (for a detailed description of the KTP, see Shikishima, Ando, Ono, Toda, & Yoshimura, 2006). After recruitment, registrants were assessed by questionnaires delivered via mail surveys.…”

“…that have been demonstrated to have 93.2% accuracy (Ooki, Yamada, Asaka, & Hayakawa, 1990). For twin pairs from whom DNA information was available through blood or buccal smears (86 pairs), zygosity was diagnosed by examining gene polymorphisms (for details, see Shikishima et al, 2006). The number of each type of twin pair who participated in photocopying of the hands was as follows: 75 identical female, 29 identical male, 22 fraternal female, 14 fraternal male, and 9 fraternal female-male opposite-sex pairs.…”

A General Factor of Personality From Multitrait–Multimethod Data and Cross–National Twins

“…The data for re-analysis came from a study of more than 651 pairs of 14-to 30-year-old Japanese twins from the Keio Twin Project, Tokyo, Japan (Shikishima et al, 2006). The twins had completed an extensively validated Japanese-language translation of the NEO …”

Psychosocial Twin Cohort Studies in Japan: The Keio Twin Research Center (KoTReC)

“…The KTS, known as the Keio Twin Project (KTP) before 2003 (Shikishima et al, 2006), was established in 1998 to conduct behavioral genetic studies in adolescence and early adulthood. Table 2 shows the variables of the updated surveys in 2013 and 2016.…”