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Dysmenorrhea is associated with epilepsy. Existing evidence is mostly limited to observational studies, which are liable to confounding and bias. This study investigated the causal relevance of dysmenorrhea on epilepsy using Mendelian randomization (MR). We extracted instrumental variants for dysmenorrhea and epilepsy from published genomewide association study data, focusing on individuals of East Asian descent. A comprehensive suite of MR estimations and sensitivity analyses was performed to ensure the robustness of the findings. Each outcome database was analyzed separately in both directi ..read more

Prior research based on Swedish data suggests that collective optimism, as measured by monthly incidence of suicides, correlates inversely with selection in utero against male twins in a population. We test this finding in the US, which reports the highest suicide rate of all high-income countries, and examine whether monthly changes in overall suicides precede changes in the ratio of male twin to male singleton live births. Consistent with prior work, we also examine as a key independent variable, suicides among women aged 15−49 years. We retrieved monthly data on suicides and the ratio of m ..read more

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The circumstances and subsequent life events of the first twins to have been born in different countries are examined. Given that both twins were born in the United Kingdom, their common citizenship was never questioned. In contrast, twins born in Canada to a legally married gay transnational couple — composed of one American and one Israeli — were assigned as citizens of different nations and their parents were regarded as if unmarried. This essay is followed by reviews of research on the Hallermann-Streiff syndrome in monozygotic (MZ) twins, the effects of technology on conjoined twin separ ..read more

Self-perception in early childhood and self-esteem in adulthood are related to a variety of aspects of psychological wellbeing. The goal of the present study was to examine genetic and familial influences on self-perception and self-esteem in separate samples of children (153 twin pairs of 5-year-olds) and adults (753 twin pairs between the ages of 25–75 years). Genetic common factor modeling showed that three facets of self-perception (physical competence, peer acceptance, and maternal acceptance) loaded onto a single heritable factor in children. Multilevel modeling showed no effects of sel ..read more

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Phenotypic variation is the result of gene expression based on complex interaction between genetic and environmental factors. It is well known that genetic and environmental factors influence gene expression, but our understanding of their relative importance remains limited. To obtain a hint for the understanding of their contributions, we took advantage of monozygotic twins, as they share genetic and shared environmental factors but differ in nonshared factors, such as environmental differences and stochastic factors. In this study, we performed cap analysis of gene expression on three pair ..read more

Astigmatism and myopia are two common ocular refractive errors that can impact daily life, including learning and productivity. Current knowledge suggests that the etiology of these conditions is the result of a complex interplay between genetic and environmental factors. Studies in populations of European ancestry have demonstrated a higher concordance of refractive errors in monozygotic (MZ) twins compared to dizygotic (DZ) twins. However, there is a lack of studies on genetically informative samples of multi-ethnic ancestry. This study aimed to estimate the genetic contribution to astigmat ..read more

The current study explored the impact of genetic relatedness differences (ΔH) and sample size on the performance of nonclassical ACE models, with a focus on same-sex and opposite-sex twin groups. The ACE model is a statistical model that posits that additive genetic factors (A), common environmental factors (C), and specific (or nonshared) environmental factors plus measurement error (E) account for individual differences in a phenotype. By extending Visscher’s (2004) least squares paradigm and conducting simulations, we illustrated how genetic relatedness of same-sex twins (HSS) influences t ..read more