Abstract 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.

Abstract Twin fetuses show a physiologically slower growth rate in the third trimester compared to singletons. Therefore, it has been suggested that the anthropometric evaluation of twins at birth should be performed using twin-specific charts. To be reliable, anthropometric charts need to fulfil certain methodological criteria to systematically review studies that have developed neonatal twin-specific anthropometric charts and assess their methodological quality. A comprehensive search was conducted across Cinahl, Embase, Global Index Medicus, PubMed, Scopus, Web of Science, Google Scholar, and relevant preprint repositories, followed by a predefined snowballing search. Two reviewers independently screened studies for eligibility, selecting those that have developed cross-sectional anthropometric charts for twins at birth, published since January 1990. Articles were excluded if they did not use anthropometric measurements at birth to construct charts. Two reviewers independently extracted data and performed quality assessment with a 16-item grading system. Sixty-eight studies were included, with all but one constructed reference, not standard, charts. Most studies did not meet the quality criteria: only 9% were prospectively designed, 34% reliably estimated gestational age, 19% reported standardized instruments, 28% described measurement techniques, and 26% did not stratify centiles by sex. This review reveals considerable methodological limitations in existing twin-specific neonatal anthropometric charts.

Abstract Triplet pregnancies are linked to a higher risk of maternal and fetal complications compared to twins and singletons. Chorionicity has been suggested as a key factor influencing perinatal and maternal outcomes in triplet pregnancies; however, more evidence is needed to clarify its role. This study aimed to assess the impact of chorionicity on adverse maternal, fetal, and neonatal outcomes in triplet pregnancies. This retrospective observational study was conducted on triplet pregnancies delivered between 2010 and 2025 at Florence University Hospital, a tertiary referral maternity center. A total of 77 triplet pregnancies were included, 51 trichorionic and 26 nontrichorionic, resulting in the delivery of 214 newborns. Maternal characteristics and obstetric, fetal, and neonatal complications were compared based on chorionicity. Multivariate logistic regression analyses identified complications most strongly associated with chorionicity, after adjusting for maternal age, mode of conception, and gestational age at delivery. Women with nontrichorionic triplet pregnancies had higher risks of delivering earlier and postpartum hemorrhage. Their newborns had significantly lower birth weights, a greater need for neonatal intensive care admission and respiratory support, and higher rates of hypoglycemia and sepsis. The multivariate logistic regression confirmed nontrichorionicity as an independent factor associated with earlier delivery and postpartum hemorrhage. Chorionicity plays an essential role in determining the prognosis of triplet pregnancies. Nontrichorionic pregnancies are strongly linked to earlier delivery, lower birth weights, and increased neonatal complications. These findings are useful for counseling patients, helping them understand specific risks based on chorionicity, although intensive prenatal care remains critical for all triplet pregnancies.

Abstract This study explores whether DNA methylation (DNAm) mediates the association between lean body mass (LBM) and cognition, as well as whether LBM mediates the association between DNAm and cognition. Based on the data of 59 monozygotic twin pairs, mediation analyses were performed using causal inference test method and mediation analyses. Average causal mediation effect (ACME), average direct effect (ADE), and total effect (TE) were calculated. Among the CpGs associated with LBM, five located within PDGFRB and RP11 genes (ACME: −0.0972−0.0463, |ACME/ADE|: 10.44%−18.30%) negatively mediated the association between LBM and cognition, while one in the PAX2 gene (ACME: 0.3510, |ACME/TE|: 11.84%) positively mediated the association. Besides, the methylation risk score (MRS) of RP11 gene (ACME: −0.0517, |ACME/ADE|: 10.64%) and MRS of all CpGs (ACME: −0.0511, |ACME/ADE|: 10.53%) negatively mediated the association of LBM with cognition. For another, LBM negatively mediated the association between the DNAm level of one CpG within UBXN6 and cognition (ACME: −0.0732, |ACME/TE|: 20.78%), while positively mediated the association between the DNAm level of four CpGs within FOXI2 and cognition (ACME: 0.2812−0.4496, |ACME/TE|: 18.15%−27.29%). It was found the DNAm in PDGFRB, RP11 and PAX2 partially mediates the association between LBM and cognition, and the association between DNAm in UBXN6 and FOXI2 with cognition is also partially mediated by LBM.

Abstract Depression, a leading cause of global disability, arises from a multifaceted combination of genetic and environmental components. This study explores the relationship between major depressive disorder (MDD) polygenic scores (PGS), characteristics and symptoms of depression, and community-shared socioeconomic factors derived from postal code data in a cohort of 12,646 individuals from the Australian Genetics of Depression Study (AGDS). Our findings reveal that people living in areas with relatively higher socioeconomic advantages and education/occupation scores are more likely to report experiencing fewer depressive symptoms during their worst depressive period, as well as fewer number of lifetime episodes. Additionally, participants who reported depression onset later in life tend to currently reside in wealthier areas. Interestingly, no significant interaction between genetic and socioeconomic factors was observed, suggesting their independent contribution to depression outcomes. This research underscores the importance of integrating socioeconomic factors into psychiatric evaluation and care, and points to the critical role of public policy in addressing mental health disparities driven by socioeconomic factors. Future research should aim to further elucidate the causal relationships within these associations and explore the potential for integrated genetic and socioeconomic approaches in mental health interventions.

Abstract Highlights from the International Symposium on Twins, held at the University of Crete on May 23−24, 2025, are summarized. The symposium, organized by Dr Maria Markodimitraki, Professor in the Department of Preschool Education at the University of Crete, attracted scholars and practitioners from Greece and around the world. Meetings with a pair of reunited monozygotic female twins, and a female twin in search of her sister, also from Greece, are described. This review is followed by summaries of twin research on neonatal outcomes, growth discordance and restriction, and romantic partners and alcohol use. Human interest stories include a book documenting the extraordinary lives of identical twins Celia and Mamaine Paget, a museum wing honoring the lost Rockefeller twin, a remarkable conjoined twinning case in India, the death of an Australian sports icon, and a most unusual triplet birth.

Abstract Childless individuals have historically faced stigma with assumptions that they lack an interest in future generations because they do not directly contribute to genetic lineage. Individuals share approximately half of their genes with siblings, 12.5% with first cousins, and 6.25% with first cousins’ children. Norwegian census data (2005−2023), reflecting similar trends to the US, UK, and other European countries, indicates a moderate difference in the number of siblings (Parents: 2.03 [women and men]; Childless: 1.88 [women], 1.94 [men]) and nieces/nephews (Parents: 3.99 [women], 4.03 [men]; Childless: 3.32 [women], 3.42 [men]) for 514,777 women and 532,834 men, respectively. By linking four generations through grandmothers, both childless and childbearing women had a slightly higher number of biological extended family members (Parents: 9.63 cousins with 15.79 children; Childless: 8.66 cousins with 12.22 children). Linking four generations for men, numbers were similar: Parents: 9.68 cousins with 15.91 children, Childless: 8.83 cousins with 12.44 children. Based on the average number of children who are parents, the childless have an average genetic fitness that is 49% of that for parents for the next generation. Both parents and childless individuals have a stake in future generations through their biological extended family.