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Whether monozygotic (MZ) and dizygotic (DZ) twins differ from each other in a variety of phenotypes is important for genetic twin modeling and for inferences made from twin studies in general. We analyzed whether there were differences in individual, maternal and paternal education between MZ and DZ twins in a large pooled dataset. Information was gathered on individual education for 218,362 adult twins from 27 twin cohorts (53% females; 39% MZ twins), and on maternal and paternal education for 147,315 and 143,056 twins respectively, from 28 twin cohorts (52% females; 38% MZ twins). Together, we had information on individual or parental education from 42 twin cohorts representing 19 countries. The original education classifications were transformed to education years and analyzed using linear regression models. Overall, MZ males had 0.26 (95% CI [0.21, 0.31]) years and MZ females 0.17 (95% CI [0.12, 0.21]) years longer education than DZ twins. The zygosity difference became smaller in more recent birth cohorts for both males and females. Parental education was somewhat longer for fathers of DZ twins in cohorts born in 1990–1999 (0.16 years, 95% CI [0.08, 0.25]) and 2000 or later (0.11 years, 95% CI [0.00, 0.22]), compared with fathers of MZ twins. The results show that the years of both individual and parental education are largely similar in MZ and DZ twins. We suggest that the socio-economic differences between MZ and DZ twins are so small that inferences based upon genetic modeling of twin data are not affected.
Background: Although supervision is believed to be an important strategy for training practitioners in evidence-based practice, little is known about how it should be organized and conducted to promote implementation fidelity. Aims: To explore supervisor behaviours that might facilitate supervisees’ proficiency in motivational interviewing. Method: In this exploratory study, ten supervisors from a primary prevention intervention of childhood obesity responded to semi-structured interviews about their supervision behaviours. A mixed method approach was used; both qualitative and quantitative data were collected and analysed. Results: The supervisors reported using several sources of information for evaluating and providing systematic feedback on supervisees’ performance. However, the majority did not use the available objective measures of proficiency as the primary source. Moreover, half of the supervisors argued that objective feedback might have a punishing effect on the supervisees. Conclusions: Variation in the use of supervision components that previous research has proposed to be potentially influential to the process and outcome may lead to less efficient supervision. Findings suggest that appropriate supervision activities conducted in each supervision session require clear supervision principles that specify the content and procedure of the supervision, as well as regular adherence monitoring of the supervision sessions.
Gestational weight gain (GWG) has in numerous studies been associated with offspring birth weight (BW) and childhood weight. However, these associations might be explained by genetic confounding as offspring inherit their mother's genetic potential to gain weight. Furthermore, little is known about whether particular periods of pregnancy could influence offspring body weight differently. We therefore aimed to explore total and trimester-specific effects of GWG in monozygotic (MZ) twin mother-pairs on their offspring's BW, weight at 1 year and body mass index (BMI) at 5 and 10 years. MZ twin mothers born 1962–1975 were identified in national Swedish registers, and data on exposure and outcome variables was collected from medical records. We analyzed associations within and between twin pairs. We had complete data on the mothers’ GWG and offspring BW for 82 pairs. The results indicated that total, and possibly also second and third trimester GWG were associated with offspring BW within the twin pairs in the fully adjusted model (β = 0.08 z-score units, 95% CI: 0.001, 0.17; β = 1.32 z-score units, 95% CI: -0.29, 2.95; and β = 1.02 z-score units, 95% CI: -0.50, 2.54, respectively). Our findings, although statistically weak, suggested no associations between GWG and offspring weight or BMI during infancy or childhood. Our study suggests that total, and possibly also second and third trimester, GWG are associated with offspring BW when taking shared genetic and environmental factors within twin pairs into account. Larger family-based studies with long follow-up are needed to confirm our findings.
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.
Gestational weight gain (GWG) is a complex trait involving intrauterine environmental, maternal environmental, and genetic factors. However, the extent to which these factors contribute to the total variation in GWG is unclear. We therefore examined the genetic and environmental influences on the variation in GWG in the first and second pregnancy in monozygotic (MZ) and dizygotic (DZ) twin mother-pairs. Further, we explored if any co-variance existed between factors influencing the variation in GWG of the mothers’ first and second pregnancies. By using Swedish nationwide record-linkage data, we identified 694 twin mother-pairs with complete data on their first pregnancy and 465 twin mother-pairs with complete data on their second pregnancy during 1982–2010. For a subanalysis, 143 twin mother-pairs had complete data on two consecutive pregnancies during the study period. We used structural equation modeling (SEM) to assess the contribution of genetic, shared, and unique environmental factors to the variation in GWG. A bivariate Cholesky decomposition model was used for the subanalysis. We found that genetic factors explained 43% (95% CI: 36–51%) of the variation in GWG in the first pregnancy and 26% (95% CI: 16–36%) in the second pregnancy. The remaining variance was explained by unique environmental factors. Both overlapping and distinct genetic and unique environmental factors influenced GWG in the first and the second pregnancy. This study showed that GWG has a moderate heritability, suggesting that a large part of the variation in the trait can be explained by unique environmental factors.
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.
In this paper the minimum ship domain in which a navigator feels comfortable is estimated. That is, we estimate the free space surrounding a ship into which no other ship or object should enter. This is very useful when estimating the maximum flow through a channel or a bridge span. The paper benefits from the introduction of Automatic Identification System (AIS) data as it is now much easier to conduct studies involving a large number of observations. Our observations are based on ships sailing in southern Danish waters during a four year period, and from the observations we estimate how closely ships pass each other and fixed objects in open sea navigation. The main result is the establishment of an empirical minimum ship domain related to a comfortable navigational distance.
Ships navigate freely when in the open sea, but their freedom of movement is reduced in areas with intense traffic, restricted draught or obstacles. In such cases, a traffic separation scheme (TSS) can be established to guide the ship traffic. This paper is based on work performed in connection with a proposed bridge across Fehmarnbelt between Denmark and Germany, and the purpose is to estimate the efficiency of a TSS guiding traffic through the main bridge openings. The efficiency in terms of getting the traffic through the traffic lanes without the TSS hindering traffic flow is an important decision parameter in the bridge design process. In this paper, we present a new “free flow” paradigm based on an innovative, dynamic application of the ship domain theory.
Background: Acquiring proficiency in motivational interviewing (MI) may be more difficult than generally believed, and training research suggests that the standard one-time workshop format may be insufficient. Although nurses represent one of the professions that have received most training in MI, training in this group has rarely been systematically evaluated using objective behavioral measures. Aims: To evaluate an enhanced MI training program, comprising a 3.5-day workshop, systematic feedback on MI performance, and four sessions of supervision on practice samples. Methods: Nurses (n = 36) in Swedish child health services were trained in MI. Skillfulness in MI was assessed using the Motivational Interviewing Treatment Integrity (MITI) Code. Effects of training were compared to beginning proficiency thresholds. Results: Participants did not reach beginning proficiency thresholds on any of the indicators of proficiency and effect sizes were small. Conclusions: The present study adds to a growing body of literature suggesting that the current standard MI training format may not provide practitioners with enough skillfulness. Moreover, the results indicate that even enhanced training, including systematic feedback and supervision, may not be sufficient. Suggestions for improved MI training are made.
A new Swedish twin register was created in 1998. All male twins born in Sweden 1973–1979 were identified in the Swedish Medical Birth Register. 3566 twins (1783 pairs) who were alive and residents of Sweden in 1997 were included in the new register. Data on birthweight, birthlength, gestational age, and so forth, were obtained from the Medical Birth Register. Record linkage was effected with the Military Service Conscription Register for the years 1991–1999. Anthropometrical data and information on blood pressure were obtained from this latter source. In 1998 a questionnaire was mailed to all twins in the register. Questions were posed about zygosity, socioeconomic conditions, lifestyle factors (physical activity, smoking habits, etc.), body shape and body size. Complete responses were obtained from 2654 twins (1327 pairs). In 2002 the cohort is being followed-up by a more extensive mailed questionnaire. Data will be collected about socioeconomic conditions, lifestyle, eating behaviour (TFEQ), body size and body shape. In the next few years genomic DNA will also be collected from buccal mucosa (using brush techniques).
The Swedish Young Male Twins Study is a population-based longitudinal twin study founded in 1997 through record-linkages of several national registers. Details on pregnancy and birth were obtained from the Swedish Medical Birth Register and used to identify 3566 male twins (1783 pairs) born in Sweden between 1973 and 1979 and resident in Sweden in 1997. A record-linkage was made between the Medical Birth Register and the Military Service Conscription Register for the years 1991 to 1999, providing information on body weight, height, blood pressure, muscle strength, cognitive ability of these twins at age 18 and 19 years. In 1998, 2002 and 2005 to 2006, the twins were surveyed on their zygosity, socioeconomic status, lifestyle factors (such as eating habits, physical activity, smoking habits, use of alcohol etc), height and weight. In 2002, additional information was collected on perceived body shape and size, and eating behavior, according to the Three-Factor Eating Questionnaire. In 2003, DNA via buccal mucosa was collected from a subset of the twins. Recent research using the Swedish Young Male Twins datasets has explored the relationships between fetal growth, body size and blood pressure in young adulthood, genetic and environmental contributions to eating behavior and physical activity, and relationships between diet and physical activity patterns with longitudinal changes in body mass index and attained waist circumference.
Many studies have found an inverse association between fetal growth and cardiovascular disease related to the metabolic syndrome in adulthood. Nevertheless, the relative importance of genetics and the intrauterine environment remain unclear. The objective of the study was to test the fetal origins hypothesis and the fetal insulin resistance hypothesis by studying the impact of fetal growth on Body Mass Index (BMI) in young adulthood. In a nationwide cohort study, the Swedish Medical Birth Register for the years 1973–1979 was linked with the Military Service Conscription Register for 1990–1999. In 1998 a questionnaire was mailed to all male twins, included in the two registers, who were alive and still resident in Sweden. The study covers the 923 male twin pairs for which full data were available. Mixed linear models were used to estimate within-pair and between-pair differences in birthweight and their relations to BMI. A weak positive association was found among the monozygotic twins for the withinpair difference in birthweight and BMI. No significant association was found among the monozygotic for the between-pair difference in birthweight and BMI. No significant associations were found for dizygotic twins. These findings do not seem to support either the fetal programming hypothesis or the fetal insulin resistance hypothesis.
It is hypothesised that the risk of schizophrenia may be elevated in children conceived following a short interpregnancy interval, when maternal folate stores are still being replenished. We examined the relationship between inter-pregnancy interval and schizophrenia risk in a longitudinal, population-based cohort. Risk of schizophrenia was increased by approximately 150% in those born following a pregnancy interval of $6 months, but was not increased if the interval after birth of the participant, before conception of the subsequent sibling, was $6 months. These findings support the hypothesis that folate (or other micronutrient) deficiency during fetal development may be an important risk factor for schizophrenia.
The orchids Dendrobium infundibulum and Cymbidium insigne are pollinated by the bumblebee Bombus eximius, which also pollinates the ericaceous shrub Rhododendron lyi, A study of the three plants and the bumblebee in maquis-like mountainous vegetation in northern Thailand suggests that they form a floral mimicry system with two mimics (the orchids) to one model (R. lyi). The flowers of the two orchid species offer no food reward to pollinators. Flowers of the three species show definite morphological and visual resemblance, and the species overlap to a great extent in flowering phenology and habitat Mimic flowers were much less numerous than model flowers, which occurred abundantly in the area. The rate of pollinaria removal was very low in both orchid species, resulting in a relatively small percentage of fruit set, especially in D. infundibulum. Infrequency of pollinator visits was, however, somewhat counterbalanced by long-lasting flowers. The pollinaria of the two orchid species are differently positioned on the bee, hence interference between the different reproductive systems is minimized. This is the first report which indicates floral mimicry from tropical Asia.
Risk factors for homicide are emerging; however, the predictive value of IQ, for which there is a strong prima facie case, has yet to be examined.
To examine the association between IQ and risk of death by homicide.
A cohort of 968 846 men, aged 18–19 years, were administered an IQ test battery at military conscription and then followed for mortality experience over two decades.
There were 191 deaths due to homicide during follow-up. In age-adjusted analyses, a high total IQ test score was associated with a reduced rate of homicide (hazard ratio (HR) per standard deviation increase in IQ score=0.49, 95% CI 0.42–0.57). A step-wise gradient was apparent across the three IQ groups (P-value for trend 50.001). After adjustment for indicators of socio-economic position and illness at conscription, this gradient was marginally attenuated (HR=0.57, 95% CI 0.49–0.67).
High IQ test scores in early adulthood were associated with a reduced risk of death by homicide.
Being a single mother may have implications for health behaviours that can also affect the child. More information about the food intakes and body weights in single v. married/cohabiting mothers and in their children is needed. Psychological dimensions of eating behaviour and self-esteem are also of relevance to explore for single mothers and their children.
Food style patterns were assessed by self-reported consumption of fruits, vegetables, sweets and soft drinks. Eating behaviour was measured by the Dutch Eating Behaviour Questionnaire and self-esteem by the Harter self-perception scale. The participants were 1781 mothers and their 12-year-old children, of whom 278 mothers (16 %) were single.
Single mothers had lower intake of fruits and vegetables and lower self-worth compared to the married and cohabiting mothers, controlling for age, education and BMI. Although single mothers did not have a higher BMI, their daughters were heavier than girls from complete families. Daughters to single mothers furthermore had a higher intake of soft drinks, higher levels of restrained eating and lower self-worth. No such difference was found for the boys.
A lower sense of self-worth and lower intake of fruit and vegetables in single mothers could be seen in the context of the social disadvantages and less social support. Girls may be more inclined to be affected by family status than the boys, seen in a more unfortunate psychological pattern and a higher body weight. Boy’s health behaviours may be more unaffected by living in single families.
We investigated associations between consumption of fruits, vegetables, sweets and soft drinks and the psychological dimensions of eating in parents and their children. The role of the parent’s characteristics for their children’s food intake was also explored.
Food intake patterns were assessed by self-reported consumption of the respective foods. Eating behaviour was measured by the Dutch Eating Behaviour Questionnaire and self-esteem by Harter self-perception scale. The participants were 1441 families (mother, father and their 12-year-old child), and additionally 354 mothers and thirty fathers.
Among parents, reported intake of fruit and vegetables were associated with restrained eating, higher self-esteem, and higher education and age. Intake of sweets was related to more external and less restrained eating, and for mothers also emotional eating. Parent’s intake of soft drink was foremost related to a younger age, and also weakly associated with psychological characteristics. The food intake of parents was more important for the children’s food intake than any other characteristics. However, children’s intake of sweets showed clear-cut positive associations with external eating.
Psychological dimensions of eating behaviour are associated with patterns of food intake, in particular for consumption of sweets, and are most prominent in the parents. The children’s food intake mirrored their parents’ intake. Being sensitive to external food cues may increase unhealthy food consumption in our society, whereas more restrained eating may indicate proneness or intention to healthier food choices among parents. Emotional eating may imply a proneness to consume sweets for comfort, in particular among mothers.
The aim of the present study was to examine the relationships between genetic susceptibility to obesity, physical activity (PA), dietary fibre, sugar and fat intakes and 4-year changes in body mass index (BMI) and attained waist circumference (WC) in a cohort of 287 monozygotic and 189 dizygotic young adult male twin pairs. Increased knowledge about interactions between genes and environment may provide insight into why some individuals are more prone to obesity than others.
Information about PA, BMI, dietary habits, WC and potential confounders was collected by questionnaire in 1998 and 2002. The cohort data were analysed by mixed linear models.
Twins with low PA attained larger WC than twins with high PA (difference 2.5 cm; 95% confidence interval (CI) 1.3, 3.6). The twins with the lowest fibre intake were found to have attained the highest WC and to have increased most in BMI (difference between highest and lowest fibre intakes: 1.6 cm, 95% CI 0.4, 2.9 and 0.45 kg m−2, 95% CI 0.15, 0.76, respectively). Furthermore, our results suggested the presence of interactions so that twins with genetic susceptibility to obesity were more prone to have larger WC if sedentary than twins without genetic susceptibility.
PA and a diet rich in fibre may be protective against weight gain among younger adult men. An interaction between PA, genes and attained WC is a novel finding which needs confirmation by other studies.