Sex differences in heritability of BMI: A comparative study of results from twin studies in eight countries

Body mass index (BMI), a simple anthropometric measure, is the most frequently used measure of adiposity and has been instrumental in documenting the worldwide increase in the prevalence of obesity witnessed during the last decades. Although this increase in overweight and obesity is thought to be mainly due to environmental changes, i.e., sedentary lifestyles and high caloric diets, consistent evidence from twin studies demonstrates high heritability and the importance of genetic differences for normal variation in BMI. We analysed self-reported data on BMI from approximately 37,000 complete twin pairs (including opposite sex pairs) aged 20-29 and 30-39 from eight different twin registries participating in the GenomEUtwin project. Quantitative genetic analyses were conducted and sex differences were explored. Variation in BMI was greater for women than for men, and in both sexes was primarily explained by additive genetic variance in all countries. Sex differences in the variance components were consistently significant. Results from analyses of opposite sex pairs also showed evidence of sex-specific genetic effects suggesting there may be some differences between men and women in the genetic factors that influence variation in BMI. These results encourage the continued search for genes of importance to the body composition and the development of obesity. Furthermore, they suggest that strategies to identify predisposing genes may benefit from taking into account potential sex specific effects.

Heritability of adult body height: A comparative study of twin cohorts in eight countries

A major component of variation in body height is due to genetic differences, but environmental factors have a substantial contributory effect. In this study we aimed to analyse whether the genetic architecture of body height varies between affluent western societies. We analysed twin data from eight countries comprising 30,111 complete twin pairs by using the univariate genetic model of the Mx statistical package. Body height and zygosity were self-reported in seven populations and measured directly in one population. We found that there was substantial variation in mean body height between countries; body height was least in Italy (177 cm in men and 163 cm in women) and greatest in the Netherlands (184 cm and 171 cm, respectively). In men there was no corresponding variation in heritability of body height, heritability estimates ranging from 0.87 to 0.93 in populations under an additive genes/unique environment (AE) model. Among women the heritability estimates were generally lower than among men with greater variation between countries, ranging from 0.68 to 0.84 when an additive genes/shared environment/unique environment (ACE) model was used. In four populations where an AE model fit equally well or better, heritability ranged from 0.89 to 0.93. This difference between the sexes was mainly due to the effect of the shared environmental component of variance, which appears to be more important among women than among men in our study populations. Our results indicate that, in general, there are only minor differences in the genetic architecture of height between affluent Caucasian populations, especially among men.

Analysis of the mouse transcriptome for genes involved in the function of the nervous system

We analyzed the mouse Representative Transcript and Protein Set for molecules involved in brain function. We found full-length cDNAs of many known brain genes and discovered new members of known brain gene families, including Family 3 G-protein coupled receptors, voltage-gated channels, and connexins. We also identified previously unknown candidates for secreted neuroactive molecules. The existence of a large number of unique brain ESTs suggests an additional molecular complexity that remains to be explored. A list of genes containing CAG stretches in the coding region represents a first step in the potential identification of candidates for hereditary neurological disorders.

Two-locus Linkage Analysis Applied to Putative Quantitative Trait Loci for Lipoprotein(a) Levels

Plasma levels of lipoprotein(a) _ Lp(a) _ are associated with cardiovascular risk (Danesh et al., 2000) and were long believed to be influenced by the LPA locus on chromosome 6q27 only. However, a recent report of Broeckel et al. (2002) suggested the presence of a second quantitative trait locus on chromosome 1 influencing Lp(a) levels. Using a two-locus model, we found no evidence for an additional Lp(a) locus on chromosome 1 in a linkage study among 483 dizygotic twin pairs.

Accuracy of Mothers' Retrospective Reports of Smoking During Pregnancy: Comparison with Twin Sister Informant Ratings

Retrospective assessment of maternal smoking or substance use during pregnancy is sometimes unavoidable. The unusually close relationship of twin sister pairs permits comparison of self-report data versus co-twin informant data on substance use during pregnancy. Information about smoking during pregnancy has been gathered from a series of mothers from an Australian volunteer twin panel (576 women reporting on 995 pregnancies), supplemented in many cases by independent ratings of their smoking by twin sister informants (821 pregnancies). Estimates of the proportion of women who had never smoked regularly (56-58%), who had smoked but did not smoke during a particular pregnancy (16-21%), or who smoked throughout the pregnancy (16-18%), were in good agreement whether based on self-report or twin sister informant data. However, informants underreported cases who smoked during the first trimester but then quit (1-3% versus 7-9% by self-report). Women who smoked throughout pregnancy (by informant report) rarely denied a history of regular smoking (

Serum inhibin A and B concentrations during the menstrual cycle in mothers of spontaneous dizygotic twins

Dizygotic twinning in humans is influenced by genetic factors suggesting inherited variation affects follicle development and predisposes to double ovulations. In a previous study, we conducted a detailed examination of follicle development and variation in hormone concentrations during the menstrual cycle in mothers of DZ twins (MODZT) compared with an age-matched control group of mothers of singletons. We did not detect differences in FSH concentrations between mothers of twins and mothers of singletons. Serum inhibin concentrations were measured by a radioimmunoassay that did not distinguish between dimeric inhibin A and B forms and free inhibin alpha subunit. We therefore analyzed the samples from this study with specific assays to determine whether concentrations of inhibin A and B were different between MODZT and controls and therefore contribute to the twinning phenotype. There were no significant differences between MONT with single ovulations and control women in inhibin A and B concentrations during the cycle, including the critical period for the selection of the dominant follicle. These data suggest that the genetic cause of twinning is not associated with changes in FSH concentrations or recognised feedback mechanisms regulating FSH release.

Zygosity Diagnosis in the Absence of Genotypic Data: An Approach Using Latent Class Analysis

For zygosity diagnosis in the absence of genotypic data, or in the recruitment phase of a twin study where only single twins from same-sex pairs are being screened, or to provide a test for sample duplication leading to the false identification of a dizygotic pair as monozygotic, the appropriate analysis of respondents' answers to questions about zygosity is critical. Using data from a young adult Australian twin cohort (N = 2094 complete pairs and 519 singleton twins from same-sex pairs with complete responses to all zygosity items), we show that application of latent class analysis (LCA), fitting a 2-class model, yields results that show good concordance with traditional methods of zygosity diagnosis, but with certain important advantages. These include the ability, in many cases, to assign zygosity with specified probability on the basis of responses of a single informant (advantageous when one zygosity type is being oversampled); and the ability to quantify the probability of misassignment of zygosity, allowing prioritization of cases for genotyping as well as identification of cases of probable laboratory error. Out of 242 twins (from 121 like-sex pairs) where genotypic data were available for zygosity confirmation, only a single case was identified of incorrect zygosity assignment by the latent class algorithm. Zygosity assignment for that single case was identified by the LCA as uncertain (probability of being a monozygotic twin only 76%), and the co-twin's responses clearly identified the pair as dizygotic (probability of being dizygotic 100%). In the absence of genotypic data, or as a safeguard against sample duplication, application of LCA for zygosity assignment or confirmation is strongly recommended.

Young people's socialisation into sport: A case study of an athletics club

This paper explores young people's (9 to 15 years old) early socialisation into sport. We draw on data from an 18-month-long ethnography of the junior section of an athletics club in England, using field notes, interviews and a psychometric questionnaire. We begin by noting a trend towards increasing numbers of younger children participating in adult-organised, community-based sport. Within this context, we investigate the extent to which Siedentop's [(1995) Junior Sport and the evolution of sport cultures, Keynote presentation to the Junior Sport Forum, Auckland, New Zealand] three main goals for young people's participation in sport, i.e. the educative, public health and elite development, are met in specific, local junior sport settings such as Forest Athletics Club (FAC). We report that most of the young people participating in the Introductory Groups at FAC begin their socialisation into sport by 'sampling' a range of sports and other activities that are available to them. We note the key features of the sampling phase for these young people, including their involvement in sports and other activities in addition to athletics, their reasons for participation, the place of competition and the importance of friendship. We report that FAC created a climate for the Samplers, intentionally or not, conducive to the development of Siedentop's educative goal, and to a lesser extent the public health and elite development goals. In concluding, we note the implications of the study for community-based programmes run by clubs.

Students' conceptions of sport and sport education

This article explores a class of Grade 5 (age 9 and 10) children’s conceptions of sport during a season of sport education at Forest Gate Primary School. The purpose, following Kirk and Kinchin (this issue), is to examine the extent to which the potential transfer of learning between school and sport as a community of practice may be possible through sport education in school physical education. With reference to student interviews and drawings we report and discuss children’s conceptions of sport, their experiences of sport outside of the school, and their emerging conceptions of sport education in light of these prior understanding and experiences. We conclude that there was an evident level of compatibility between students’ experiences of sport education and their conceptions of sport more broadly.

Muscularity, the habitus and the social construction of gender: Towards a gender-relevant physical education

This paper begins to develop the concept of gender-relevant physical education, combining the work of Pierre Bourdieu and his notion of the habitus and feminist philosopher Iris Marion Young's analysis of feminine motility. It draws on data generated from a study of young people's articulation of the relationships between muscularity, physicality and gender. The social construction of the body has been of central importance to the construction of femininities and masculinities, and has formed an enduring meta-theme through much of the research on physical education and gender. We build on the young people's insights to argue that Bourdieu's notions of the habitus and the exchange of physical capital provide a useful means of conceptualizing issues of embodiment and gender in school physical education and sport. We conclude by sketching an outline of gender-relevant physical education as a process of interrupting the habitus.

Listening to young people's voices: Youth sports leaders' advice on facilitating participation in sport

This article reports on a study that accepts the proposal that we listento the voices of young people in relation to sport and physical recreation.The study sought the advice of young sports leaders on what can be done to facilitate young people’s involvement in sport. The study used group interviews (Nominal Group Technique) with over 600 14–18-year-olds toelicit responses to a single question, ‘What can be done to help young people participate in sport?’ This article focuses on young people’s views on issues to do with climate and conditions. We argue that, while their advice offers support for some current initiatives in youth sport, it also provides new insights and challenges and suggests a reordering of existing priorities for youth sport and leisure provision.

Social positioning and the construction of a youth sports club

This article uses the concept of social positioning to explore the construction of a youth sports club by young people, their parents and coaches. The year-long ethnography of Forest Athletics Club (FAC) identified two athlete positions of Samplers and Beginning Specializers. Four parents’ positions were identified, those of Non-Attenders, Spectators, Helpers and Committed Members. One coach position was the Committed Volunteer. Each of these positions was interdependent. Particular expectations, practices and values were attached to these positions. It is argued that the club operates according to multiple agendas and that FAC is a complex and dynamic social phenomenon that is practised differently by the three groups of key players.

Listening to the 'voices' of students with severe learning difficulties through a task-based approach to research and learning in physical education

In this article, Hayley Fitzgerald, Anne Jobling and David Kirk consider the physical education and sporting experiences of a group of students with severe learning difficulties. Their study is thought provoking, not only because of the important and somewhat neglected subject matter, but equally for the research approach adopted. The way in which the study engaged with the students and the insights gained from that engagement will be of particular interest to practitioner researchers.