Obesity represents a major global public health concern. Body fat percentage (BF%) is a key indicator for assessing adiposity and provides a more precise estimation of obesity-related health risks compared to the traditional body mass index (BMI). Accumulating evidence suggests that BF% is influenced by both genetic and environmental factors. However, most genetic studies on BF% have been conducted in European and American population, with limited data available from Chinese cohorts. To address this gap, a classical twin study was conducted using data from the Qingdao Twin Registry in China to estimate the heritability of BF% adjusted for age, sex, and BMI. This study included Han Chinese twins registered in the Qingdao Twin Registry. This study included 344 middle and old-aged Chinese twin pairs (217 monozygotic and 127 dizygotic). comprising 327 males and 361 females. The median age of participants was 50 (interquartile range [IQR]:12) years, with BF% of 27.6 (11.4) %. Model fitting indicated that the best-fitting model was AE model. The additive genetic effect (A) accounted for 54% (95% CI [44, 59) of the total variance, while unique environmental effect (E) contributed 46% (95% CI [37, 56]). In conclusion, this twin-based study provides robust evidence for a moderate genetic contribution (heritability = 54%) to BF% in a middle- and old-aged Qingdao population.

Attention deficit/hyperactivity disorder (ADHD) is associated with an increased risk of cardiovascular diseases (CVDs). However, whether this is a causal relation and how ADHD may predispose to a higher risk of CVD needs to be determined. We aimed to assess the causal association between ADHD and both coronary artery disease (CAD) and heart failure (HF), and to quantify the mediating effects of potential modifiable mediators. We conducted a two-step, two-sample Mendelian randomization (MR) study using SNPs as genetic instruments for exposure and potential mediators. Leveraging summary data on the latest genomewide association studies for ADHD, proposed mediators (i.e., metabolic factors, inflammatory factors, lifestyle behaviors, psychiatric disorders, and educational attainment), CAD and HF, we decomposed the total effect of ADHD on each outcome into direct and indirect effects through multiple mediators. Genetically predicted ADHD was associated with increased odds of CAD (OR 1.13; 95% CI [1.07, 1.19]), with educational attainment (EA) being the largest contributor (32.27% mediation, 95% CI [18.33%, 56.93%]). Body mass index (BMI), type 2 diabetes (T2D), EA, smoking initiation (SI), and depression jointly explained 83.59% (95% CI [63.95%, 101.49%]) of the association. Genetically predicted ADHD was associated with increased odds of HF (OR 1.11; 95% CI [1.05, 1.19]), with SI being the largest contributor (35.87% mediation, 95% CI [13.75%, 100.14%]). BMI, T2D, and SI jointly explained 82.39% (95% CI [45.90%, 131.60%]) of the association. The findings support a causal relationship between ADHD and both CAD and HF. Several modifiable risk factors substantially mediate these associations, suggesting potential targets for interventions aimed at reducing CVD risk in individuals with ADHD.

A simple application of urn models is useful in spelling out the way in which, in abstraction, if the parents are distributed in Hardy-Weinberg form, that form is reproduced in offspring with nonrandom mating. A measure of divergence from random mating is proposed and illustrated by numerical examples. The scope of urn models of stochastic processes in population genetics theory is set out.

This study evaluated the growth trajectories of twins from birth to school age, focusing on weight and height z scores of children born in São Paulo. The longitudinal study comprised 188 healthy twins (M = 9.13 years; SD = 2.16). Weight data were obtained from birth records and reassessed at school age, and height at school age. Singleton birth weights and standard growth curves were used as reference points. Overall, the proportion of children with z scores below the median decreased significantly, from 98.3% at birth to 31.4% at school age. At birth, the dispersion of z-scores below the median was significantly greater among monochorionic compared to dichorionic twins (2.051 vs. 1.701), but this difference was no longer observed at school age (1.861 vs. 0.976). In total, 68.8% of the twins showed improved weight development, with no cases of deterioration. While monozygotic (MZ) and dizygotic (DZ) twin pairs exhibited comparable intertwin birth-weight differences, by school age MZ pairs exhibited more similar weights, whereas DZ pairs showed significantly greater weight discrepancies. For height at school age, mean height z scores were within the expected range for singletons. No significant differences were observed between monochorionic and dichorionic twins, whereas MZ pairs showed smaller within-pair height differences than DZ pairs. These findings suggest that although chorionicity plays an important role during the perinatal period — particularly due to the lower birth weights observed among monochorionic twins — its influence diminishes over time. By school age, weight and height differences are primarily determined by zygosity.

Assessing the size of twins at birth using charts developed for singletons may over diagnose small for gestational age in this sub-population. The study aimed to produce international, twin-specific, newborn size normative charts by gestational age and sex. This longitudinal observational study in eight geographically diverse settings prospectively collected data between May 2009 and August 2013 from healthy pregnant women and their newborn twins. The participants were enrolled as part of the INTERGROWTH-21st study, and recruited based on World Health Organization recommendations for evaluation of anthropometric measures. All the women met, in addition to the underlying population characteristics of low perinatal risk, strict individual criteria for a population at low risk of impaired fetal growth. Newborn weight, length and head circumference measures were collected independently in duplicate by two trained anthropometrists within 12 hours of birth using identical equipment and protocols at all sites. From 1034 multiple pregnancies, after exclusions of condition such as smoking, high maternal BMI, and congenital malformations, the final sample was 864 twin newborns. Most of the twins were below the 50th centile of the INTERGROWTH-21st standards for singletons. We present international newborn size normative charts for twins using the same methodological approach adopted to construct the singleton standards.

The studies on the association between maternal gestational weight gain (GWG) and spontaneous preterm birth (SPTB) in twin pregnancies are limited and inconsistent. There are no standardized guidelines for GWG in twin pregnancies in China. This retrospective cohort study included 1510 women who delivered living twins from January 1, 2015 to December 31, 2019. The basic demographics and outcomes of mothers and neonates were listed, and logistic regression was used to analyze the relationship between GWG and SPTB in the total population and different subgroups. In the overall population, 464 (30.7%) women had inadequate GWG, and 316 (20.9%) women had excess GWG. Compared to women with adequate GWG, women with inadequate GWG had a significantly higher risk of SPTB (adjusted odds ratio [aOR]: 2.46, 95% CI [1.92, 3.15]), while women with excess GWG also had a significantly higher risk of SPTB (aOR: 1.48, 95% CI [1.12, 1.95]). Both inadequate GWG and excess GWG had a significantly higher risk of SPTB in normal-weight women and women with dichorionic diamniotic twins. Only IGWG was significantly associated with SPTB in women with monochorionic diamniotic twins and underweight women. Our findings indicate that inadequate GWG and excess GWG were significantly associated with a higher risk of SPTB, providing an empirical basis for establishing weight gain guidelines for women with twin pregnancies in China.

This position statement provides guidelines for health professionals who are considering online or direct-to-consumer genetic testing for their patients. It presents the major issues around online and direct-to-consumer (DTC) testing including how it is accessed, motivations for accessing testing and how to return these results. Online or DTC recommendations include: (1) DTC testing should only be done by individuals/consumers who are well informed, aware of the risks, benefits and limitations of testing, and able to consent for their DNA to be collected, analyzed and potentially stored. Where possible, individuals/consumers should also be aware of the alternative option of undertaking testing through healthcare professionals in a clinical context, and the benefits of this. (2) Decisions about having a child tested should be based on peer-reviewed, published evidence. Genomics testing for children should be within a clinical context where parents are informed, have access to clinical support and professional genetic counseling about this decision, as well as support for the range of results received. (3) Parents considering direct-to-consumer testing on their newborn are counselled, or given information, to encourage them to have standard government funded newborn bloodspot screening testing on their newborn. (4) When choosing an online genomic test, preference should be given to tests undertaken in accredited laboratories offering tests accredited with the Therapeutic Goods Administration. (5) Results obtained through methods other than direct analysis from a laboratory accredited to perform genomic testing to inform human health and wellbeing should be interpreted with caution. The HGSA recommends that such results must be confirmed in an accredited diagnostic laboratory prior to relying on them to inform options for treatment, surveillance or risk reduction, or before undertaking cascade testing in family members. (6) When individuals are concerned about their health, they should consult an appropriate healthcare professional to decide whether an online genomic test is appropriate and discuss how useful test results could be to make health-related decisions.

This article presents an overview of the life histories of reared-apart twins from the Philippines. One twin always knew he was a twin, but for the other twin the discovery at age 15 came as a shock. This essay is followed by summaries of recent twin research of interest. Topics include twin discordance for multisystem inflammatory syndrome, in vitro fertilization (IVF) twins and possible associations with impaired hearing, the writings of monozygotic (MZ) twins, and an update on MZ twins with Feingold syndrome whom I have covered in a previous issue of this journal. This essay concludes with several twin-related human interest stories, namely conjoined twin girls from Sri Lanka, conjoined twin boys from Papua, New Guinea, recent information concerning conjoined twins Abby and Brittany Hensel, a twin sentenced for criminal activities, and accurate identification of an identical twin culprit by DNA sequencing.