The COllaborative project of Development of Anthropometrical measures in Twins (CODATwins) project is a large international collaborative effort to analyze individual-level phenotype data from twins in multiple cohorts from different environments. The main objective is to study factors that modify genetic and environmental variation of height, body mass index (BMI, kg/m2) and size at birth, and additionally to address other research questions such as long-term consequences of birth size. The project started in 2013 and is open to all twin projects in the world having height and weight measures on twins with information on zygosity. Thus far, 54 twin projects from 24 countries have provided individual-level data. The CODATwins database includes 489,981 twin individuals (228,635 complete twin pairs). Since many twin cohorts have collected longitudinal data, there is a total of 1,049,785 height and weight observations. For many cohorts, we also have information on birth weight and length, own smoking behavior and own or parental education. We found that the heritability estimates of height and BMI systematically changed from infancy to old age. Remarkably, only minor differences in the heritability estimates were found across cultural–geographic regions, measurement time and birth cohort for height and BMI. In addition to genetic epidemiological studies, we looked at associations of height and BMI with education, birth weight and smoking status. Within-family analyses examined differences within same-sex and opposite-sex dizygotic twins in birth size and later development. The CODATwins project demonstrates the feasibility and value of international collaboration to address gene-by-exposure interactions that require large sample sizes and address the effects of different exposures across time, geographical regions and socioeconomic status.

We analyzed birth order differences in means and variances of height and body mass index (BMI) in monozygotic (MZ) and dizygotic (DZ) twins from infancy to old age. The data were derived from the international CODATwins database. The total number of height and BMI measures from 0.5 to 79.5 years of age was 397,466. As expected, first-born twins had greater birth weight than second-born twins. With respect to height, first-born twins were slightly taller than second-born twins in childhood. After adjusting the results for birth weight, the birth order differences decreased and were no longer statistically significant. First-born twins had greater BMI than the second-born twins over childhood and adolescence. After adjusting the results for birth weight, birth order was still associated with BMI until 12 years of age. No interaction effect between birth order and zygosity was found. Only limited evidence was found that birth order influenced variances of height or BMI. The results were similar among boys and girls and also in MZ and DZ twins. Overall, the differences in height and BMI between first- and second-born twins were modest even in early childhood, while adjustment for birth weight reduced the birth order differences but did not remove them for BMI.

A trend toward greater body size in dizygotic (DZ) than in monozygotic (MZ) twins has been suggested by some but not all studies, and this difference may also vary by age. We analyzed zygosity differences in mean values and variances of height and body mass index (BMI) among male and female twins from infancy to old age. Data were derived from an international database of 54 twin cohorts participating in the COllaborative project of Development of Anthropometrical measures in Twins (CODATwins), and included 842,951 height and BMI measurements from twins aged 1 to 102 years. The results showed that DZ twins were consistently taller than MZ twins, with differences of up to 2.0 cm in childhood and adolescence and up to 0.9 cm in adulthood. Similarly, a greater mean BMI of up to 0.3 kg/m2 in childhood and adolescence and up to 0.2 kg/m2 in adulthood was observed in DZ twins, although the pattern was less consistent. DZ twins presented up to 1.7% greater height and 1.9% greater BMI than MZ twins; these percentage differences were largest in middle and late childhood and decreased with age in both sexes. The variance of height was similar in MZ and DZ twins at most ages. In contrast, the variance of BMI was significantly higher in DZ than in MZ twins, particularly in childhood. In conclusion, DZ twins were generally taller and had greater BMI than MZ twins, but the differences decreased with age in both sexes.

For over 100 years, the genetics of human anthropometric traits has attracted scientific interest. In particular, height and body mass index (BMI, calculated as kg/m2) have been under intensive genetic research. However, it is still largely unknown whether and how heritability estimates vary between human populations. Opportunities to address this question have increased recently because of the establishment of many new twin cohorts and the increasing accumulation of data in established twin cohorts. We started a new research project to analyze systematically (1) the variation of heritability estimates of height, BMI and their trajectories over the life course between birth cohorts, ethnicities and countries, and (2) to study the effects of birth-related factors, education and smoking on these anthropometric traits and whether these effects vary between twin cohorts. We identified 67 twin projects, including both monozygotic (MZ) and dizygotic (DZ) twins, using various sources. We asked for individual level data on height and weight including repeated measurements, birth related traits, background variables, education and smoking. By the end of 2014, 48 projects participated. Together, we have 893,458 height and weight measures (52% females) from 434,723 twin individuals, including 201,192 complete twin pairs (40% monozygotic, 40% same-sex dizygotic and 20% opposite-sex dizygotic) representing 22 countries. This project demonstrates that large-scale international twin studies are feasible and can promote the use of existing data for novel research purposes.

Stress Corrosion Cracking (SCC) has been detected in Boiling Water Reactors (BWRs) on core shrouds and primary water re-circulation piping made of low carbon stainless steels. Material hardening strongly affects SCC propagation behavior, and SCC growth rates increase with increasing hardness of austenitic stainless steels caused by cold work or neutron irradiation.

Research work has been conducted in the authors’ laboratories with the aim of improving SCC resistance using chemical composition control of stainless steels. It has been previously reported that high stacking fault energy (SFE) materials showed better SCC resistance than low SFE materials due to hardening being suppressed in high SFE materials. In the present study, SCC growth rate (CGR) tests were performed using 15% cold worked Types 316L and 25Cr-20Ni stainless steels in a simulated BWR water environment. The 25Cr-20Ni stainless steel used has high SFE value due to chemical composition control and measured SCC growth rates were lower than those of low SFE stainless steels.

However, oxidation behavior is one of the more important factors influencing SCC of austenitic stainless steels in addition to material hardening behavior, and the influence of the chemical composition control necessary to increase SFE on oxidation behavior in BWR primary coolants is still unclear. In this study, therefore, immersion tests using Types 316L and 25Cr-20Ni stainless steel specimens were also conducted in the simulated BWR water environment. The surface oxide films on the specimens were then analyzed with micro-Raman spectroscopy and glow discharge optical emission spectroscopy in order to help clarify the oxidation behavior.

The results of these tests and analyses showed that the NiFe2O4 content of the outer oxide layers on the high SFE stainless steels was higher than that on the low SFE stainless steels. The inner oxide film on the 25Cr-20Ni stainless steel also had a high chromium content.

Based on the above results, SCC resistance and oxidation behavior of high SFE austenitic stainless steels in a simulated BWR water environment will be discussed.

The present study aimed at clarifying the characteristics of twins' physical growth. First, 557 pairs of normal Japanese twins were analyzed according to the following three life stages: (1) intrauterine growth, (2) body weight and height from birth to 6 years, and (3) body weight and height at school age (from 6 to 11 years). The following results were obtained. 1. Intrauterine growth of twins was very different from that of singletons, especially as regards weight, so twins should be estimated by twin standards. 2. Size deficit at birth was appropriately recovered over the first 6 years. 3. No size deficit was observed by school age. Second, the similarity of bodyweight and height according to zygosity was analyzed using 605 pairs of normal Japanese twins, 427 monozygotic (MZ), 113 same-sexed dizygotic (DZ) and 65 opposite-sexed DZ pairs. The similarity between MZ and DZ pairs was almost the same at birth. However, MZ pairs became increasingly more similar with age, whereas DZ pairs became more dissimilar. This tendency was very clearly seen through early infancy, thus suggesting that genetic factors became more apparent during this life stage.

Subjects were 74 twin pairs, 61 MZs and 13 same-sexed DZs who entered the High School affiliated with Tokyo University, Japan. Their mothers also participated. The twins’ zygosity was previously identified by many genetic markers. This study aimed at clarifying the effectiveness of zygosity diagnosis by questionnaires distributed to twins’ mothers. The questionnaire consisted of three questions concerning the degree of similarity of twins at one year of age; whether they were confused, and if so, by whom. It was slightly modified from that reported earlier by Ooki et al [11] for twins themselves. According to the degree of similarity of the twins, points were allotted thus: from 1 to 3 points for answers to questions (1) and (2) and from 1 to 4 points for answers to questions (3). The sum of the points was calculated, then ranged from 3 to 10. Zygosity was determined by the sum of these points. If the sum was 3-6, the twin pairs were considered MZ and if the sum was 7-10 DZ. It was revealed that more than 90% of twins were identified correctly as MZ or DZ by applying this cutting point and this result was in accordance with that obtained by use of discriminant function analysis. Moreover, the accuracy of the mothers’ responses was nearly the same as that obtained by the questionnaire for twins themselves. It was concluded, therefore, that the information from twins’ mothers is as correct as that from twins themselves. This questionnaire is simple, practical and especially useful when twins are still too young to participate personally.

This study showed that biological handicap with many complications at birth was much more recognized in the second-born than in the first-born twins. One of the most prominent intrapair differences was, for example, the weight at birth. However, intrapair differences, which were observed also in other physical measurements, diminished gradually with age. Moreover, as for intellectual ability, which was represented by the scores of the entrance examination test or standard achievement test, no remarkable influences due to handicap of the second-born were identified. Thus, it was concluded that the biological handicap seen in the second-born twin at birth did not give any significant effect on later development.

Subjects were 189 twin pairs, 165 MZ and 24 same-sexed DZ, who entered the junior high school affiliated to Tokyo University (sample T), and 93 twin pairs, 71 MZ and 22 same-sexed DZ, who were registered at Kinki University (sample K). The zygosity was previously identified by many genetic markers, and this study aimed at zygosity diagnosis by questionnaire. The latter included three questions: “How are you alike?”, “How often are you mistaken?”, and “By whom are you mistaken?”. According to the degree, 1-3 points, 1-3 points, and 1-4 points were given for each question, and the sum of the points of each pair of twins was calculated. Zygosity was determined by the sum of points, distributed from 6 to 20. Namely, if the sum was 6-13, the twin pair was considered MZ, and if the sum was 14-20, DZ. More than 90% of twins were diagnosed correctly by use of this cutting point. This result was in accordance with that obtained by use of discriminant function analysis. It is concluded that zygosity diagnosis by questionnaire is convenient and useful, in particular for epidemiological research.

The present study deals with the relationship between blood uric acid level and human behavior. Subjects were 37 MZ and 7 DZ twins aged from 18 to 45 years. In males, blood uric acid level increased with age, while it decreased with age in females. Blood uric acid level was corrected and standardized using regression lines separately for males and females. The distribution of standardized uric acid level corresponded well with the theoretical curve of normal distribution. The intraclass correlation coefficient for standardized uric acid level was r = 0.370 (P < 0.05) for the 37 MZ twins, but not significant for the 7 DZ twins. These findings suggest that blood uric acid level is genetically controlled. By the analysis of 12 personality traits in YG (Yatabe-Guilford) character test, it was revealed that “General activity” was more controlled by genetically than environmentally. In the evaluation of the correlation between standardized uric acid level and the YG 12 personality traits, significant correlation was observed in “Lack of agreeableness” and “Rhathymia”. Since these two personality traits include the factor of “activity”, it is concluded that the plasma uric acid level and activity in a broader sense are under genetic control. This conclusion is consistent with the generally accepted view that persons with high uric acid level are more active and energetic than those with low level.