The objective was to examine the association between several obesity-related nongenetic behaviors and body mass index (BMI) and waist circumference (WC) in young adult twins using reports from both twins on their similarities and differences. A total of 713 monozygotic (MZ) and 698 same-sex dizygotic (DZ) twin pairs aged 22–28 years filled in structured questionnaires to compare their eating, physical activity and dieting behavior with their co-twin's behavior, and to report their own eating and exercise habits. In both MZ and DZ pairs, the co-twins for whom both twin pair members concordantly answered that this twin eats more, snacks more, eats more fatty foods and sweet and fatty delicacies, chooses less healthy foods, eats faster and exercises less, had significantly higher BMIs (0.6–2.9 kg/m2) and WCs (1.5–7.5 cm). Multivariate regression analysis identified co-twin differences in the amount of food consumed as the strongest independent predictor of intrapair differences in BMI (β = 0.63 and 1.21, for MZ and DZ, respectively, p < .001) and WC (β = 1.52 and 3.53, for MZ and DZ, respectively, p < .001). Higher leisure-time physical activity and healthier dietary choices clustered in the same subjects. The measurement of habitual dietary intake and physical activity has previously relied on subjective self-reports that are prone to misreporting. By using comparative measures within twin pairs we found that the amount of food consumed is the major contributor to obesity independent of genetic predisposition.

Background: Exaggerated cardiovascular reactivity to stressful stimuli may be a risk factor for the development of hypertension. The genetic influence on blood pressure (BP) reactivity to stress and its control mechanisms has been receiving considerable support. This study aims at examining the heritability of BP and its intermediate hemodynamic phenotypes to acute stress in a homogeneous Arab population. Methods: Parameters were computed from continuous BP, electrocardiography and impedance cardiography measurements, during rest, word conflict (WCT) and cold pressor (CPT) tests. Heritability estimates (h2) were obtained using the variance components-based approach implemented in the SOLAR software package. Results: Reactivity scores for WCT and CPT increased significantly (P < .05) for systolic (SBP), diastolic (DBP), heart rate (HR), cardiac output (CO), and total peripheral resistance (TPR). They decreased significantly (P < .05) for stroke volume (SV), left ventricular ejection time (LVET), end diastolic (EDI) and cardiac contractility (IC) indices. Univariate analysis detected heritability estimates that ranged from 0.19–0.35 for rest, 0.002–0.40 for WCT and 0.08–0.35 for CPT. Conclusion: In this unique cohort, resting as well as challenged cardiovascular phenotypes are significantly influenced by additive genetic effects. Heritability estimates for resting phenotypes are in a relatively narrow range, while h2 for their reactivity is somewhat broader with lower estimates. Further analyses of this study may offer important opportunities for gene finding in hypertension. What is Known About the Topic: (1) cardiovascular reactivity to stress predicts cardiovascular disease; (2) genetic susceptibility plays an important role in stress reactivity. Family studies using the cold pressure test reported significant heritability for blood pressure. What this Study Adds: (1) this cohort is from five highly consanguineous isolated Arab pedigrees with genetically verified genealogical records and environmental homogeneity; (2) This is the first study to estimate heritability of detailed intermediate hemodynamic phenotypes that make up normal blood pressure.

Although genetic basis of childhood temperament has been well documented in western populations, little is known about whether genes play an important role in childhood temperament in East Asians. The present study examined mother's ratings of Emotionality, Activity, and Sociability (EAS) in 894 pairs of 2- to 9-year-old South Korean twins. The best-fitting model indicated that 34 to 47% of the variances of the EAS were attributable to genetic factors, with the remaining variances being due to the effects of environmental experiences unique to each child. Common family environmental factors were negligible. Genetic variances for Activity and Sociability were primarily nonadditive, whereas those for Emotionality were additive. In spite of well known cultural differences in child rearing practices, social values, and the mean levels of temperament between East Asian and western populations, the pattern of additive vs. nonadditive gene actions and heritability estimates found in the present sample were remarkably similar to those reported in western twin samples. There were no significant age or sex differences in genetic or environmental influences. Overall, these results corroborate cross cultural generality of genetic influences on childhood temperament.

We reanalyze previously published data on 309 MZ and 333 DZ twin pairs aged 25 to 74 years from the MIDUS survey, a nationally representative archived sample, to examine how much of the genetic covariance between a general factor of personality (GFP), a lower-order life history factor, and a general physical and mental health factor, is of the nonadditive variety. We found nonadditive genetic effects (D) could not be ruled out as a contributor to the shared variance of these three latent factors to a Super-K Life History factor. We suggest these genetic correlations support the view that a slow (K-selected) life history strategy, good health, and the GFP coevolved and are mutually coadapted through directional selection.

Evidence of a positive association between birthweight and IQ has been established in several studies. Analyses of within twin pair differences in birthweight and IQ have been used to shed light on the basis of the association. The strength of this approach is the possibility of controlling for both unmeasured common childhood–environmental factors as well as genetic factors shared by the co-twins. Two twin studies suggest the existence of genetic mediation between birthweight and IQ, that is, common genetic factors influence both fetal growth and IQ in childhood, while two other twin studies find no evidence of such mediation. In the present study we use a large population-based national register study of 2,413 Danish twin-pairs from birth cohorts 1986–1990, of which we have zygosity information on 74%. We perform individual level as well as intra-pair analyses of birthweight and school achievements at age 16. For both sexes we observed a monotonic increase in academic performance with increasing percentiles of birthweight. However, we did not find that this association is due to genetic mediation.

The Older Australian Twins Study (OATS) was recently initiated to investigate genetic and environmental factors and their associations and interactions in healthy brain ageing and ageing-related neurocognitive disorders. The study extends the classic MZ-DZ design to include one or two equivalently aged siblings for each twin pair and utilizes the rich resources of the Australian Twin Registry. The study has a number of distinguishing features including comprehensive psychiatric, neuropsychological, cardiovascular, metabolic, and neuroimaging assessments, a longitudinal design and links with a brain donor program. The study measures many behavioral and environmental factors, but in particular lifetime physical and mental activity, physical and psychological trauma, loss of parent early in life, later losses and life events, early-life socioeconomic environment, alcohol and drug use, occupational exposure, and nutrition. It also includes comprehensive cardiovascular assessment, blood biochemistry, genetics and proteomics. The socio-demographic and health data on the first 172 pairs of twins participating in this study are presented. Prevalence of mild cognitive impairment is 12.8% and of dementia 1.5% in the sample. The target sample size is 1000, with at least 400 pairs of twins aged 65–90 years. The cohort will be assessed every two years, with in-depth assessments being repeated. OATS offers an excellent opportunity for collaboration with other similar studies as well as researchers who share the same interests.

Strong geographical variations in the twinning rate have been presented in the literature. In general, the rate is high among people of African origin, intermediate among Europeans and low among most Asiatic populations. In Europe, a progressive increase has occurred in the twinning rate from south to north, with a minimum around the Basque provinces. The highest twinning rates in Europe have been found among Nordic populations with the exception of the Saamis (Lapps). Within larger populations, some small isolated subpopulations have been identified to have extreme, mainly high, twinning rates. In this study, we investigated the regional variation of the twinning rate in Sweden. We analysed twinning rates for different counties for the period 1751–1850. From the middle of the 19th century, the environmental and genetic differences have decreased and the regional twinning rates have converged towards a common decreased level. The models applied have the geographical coordinates as regressors. The optimal model for the twinning rate has the longitude, the latitude and their product as regressors, indicating both horizontal and vertical trends. According to this model, the maximum twinning rate in Sweden is located in the eastern part of central Sweden, mainly on the island of Gotland and in the counties around Stockholm. Relatively low twinning rates are seen in the western and northern parts of Sweden.

Dizygotic twinning rates have changed over time, which has been seen as a sign of a decline in fecundity. Since a woman's birthweight has been shown to be a marker of her fecundity, maternal birthweight may correlate with subsequent twinning rates. In the Danish National Birth Cohort (1996–2002), we examined if maternal birthweight, and whether she was born at term or preterm, correlated with her probability of multiple birth. For 20,719 live born infants, we had self-reported information about maternal birthweight, collected during the first wave of the 7-year follow-up, and information on multiple births from record linkage. The association between maternal birthweight and multiple births was investigated by use of logistic regression and presented as odds ratios (ORs) with 95% confidence intervals (CIs). Compared to women born at term with a birthweight of 3001–4000 g, women with a birthweight > 4500 g appeared to have higher chance of multiple birth while women with a birthweight of 4001–4500 had a lower chance, especially if the analysis was restricted to women with a BMI < 25 (Adjusted ORs 2.3 [1.0–5.4] and 0.4 [0.2–0.9] respectively). Odds ratios for dizygotic twinning were of the same magnitude. In women with a BMI ≥ 25, no obvious pattern was present. Our findings do not indicate that twinning is a fecundity indicator. Women with a birthweight that may indicate a pregnancy complicated with gestational diabetes had the highest rate of multiple birth. These findings are new and should be put to a critical test in other data sources.

The purpose was to compare the sella turcica morphology of individuals within pairs of monozygotic twins with normal karyotype and to analyze the similarity between the observed morphology and the morphology of non-twins at the same age with normal karyotype. Profile radiographs from 84 individuals of 42 twin pairs (18 male and 24 female pairs, aged 18–23 years) comprised the material. Sella turcica measurements from non-twins aged 6–21 years were used as normal reference. Length, depth and diameter of the sella turcica were measured and controlled by re-measurements. Pearson's correlation coefficient was used for comparison of individuals within twin pairs. For comparison of twins and non-twins, normal standard values for length, depth and diameter were subtracted from the twin values. For the mean values of these differences, confidence limits p values and t values were calculated. The study showed that the size of the sella turcica may be partly similar and partly dissimilar within the pair of monozygotic twins. Statistical evaluation of the data showed correlations between length, depth and diameter of the sella turcica between the two twin individuals in the same twin pair. Differences in sizes are observed between individuals in the twin material and individuals in the non-twin material. As a conclusion, the twin males were more similar within the twin pair, but deviated more from the non-twin material than the females. Female twins had more discrepancy within the twin pair, but deviated less from the non-twin material than the males.

Objective: Discordance in nuchal translucency measurements in monochorionic diamniotic twin pregnancies was assessed as predictor of Twin-to-Twin Transfusion Syndrome. Study Design: A total of 61 monochorionic diamniotic twins were enrolled. Nuchal translucency (NT) and crown-rump-length (CRL) discordance was calculated as the percentage of delta NT and CRL (absolute difference NT/CRL fetus 1 and fetus 2) of the largest measurement, and correlated with subsequent development of Twin-to-Twin Transfusion Syndrome. Results: Twin-to-Twin Transfusion Syndrome developed in 14/61 (23%) of cases. A NT discordance of 20% or more best predicted Twin-to-Twin Transfusion Syndrome development, with a sensitivity of 64% and a specificity of 78%. We found a positive predictive value of 50% and negative predicted value of 86% for Twin-to-Twin Transfusion Syndrome development if NT discordance was 20% or more. Conclusion: NT discordance of more than 20% in monochorionic diamniotic twins is associated with an increased risk for subsequent development of Twin-to-Twin Transfusion Syndrome, and with earlier presentation of symptoms.

Aunique case of artificially conceived twins is described. The infants involved are unrelated to one another, as well as to the mother who carried them. The question of whether these individuals meet scientific criteria for being twins is considered, as is the issue of whether their parents are really parents of twins. Next, the International Society for Twin Studies acknowledges the life and work of its late esteemed colleague, Dr Robert Derom. His professional accomplishments on behalf of twins and twin research will be remembered, as will his helpfulness and generosity to fellow investigators. This tribute to Dr Derom is followed by reviews of new research on the pathophysiology of the twin transfusion syndrome and the use of discordant MZ twins (co-twin control) in behavioral research. The final section provides a review of the athletic talents of two sets of MZ twin tennis players, and the creative skills of a set of MZ twin designers.