Although previous studies have identified negative relationships between cognitive ability and emotional problems (EP), mechanism explaining these relationships remained unclear. This study evaluated ...two explanatory models using bivariate moderation model-fitting analysis in a twin design. The resilience model suggests that high cognitive ability decreases the risk of EP in adverse settings, and the scarring model suggests that EP symptoms lead to persistent cognitive deficits following onset. The Standard Progressive Matrices Plus (SPM) and EP scale were administered to a sample of 3,202 twins (mean age = 14.62 ± 1.74 years) attending public schools in Nigeria. The results of bivariate moderation model-fitting analyses only supported the resilience model. Moderation effects were not significant in the scarring model when genetic and environmental influences were incorporated. The best-fitting bivariate moderation model assuming the resilience model yielded a genetic correlation of − 0.57 (95% CI = − 0.40, − 0.84) with no significant environmental correlations. Moreover, the SPM moderated the environmental, not genetic, influences on EP, such that environmental influences were strong when protective factors were absent (low SPM) and weak when these were present (high SPM). These results indicate the need to develop targeted prevention and intervention strategies for EP in adolescents displaying low cognitive ability in deprived settings.
Over the previous decades, twinning rates worldwide have increased remarkably. This study aimed to describe changes in multiple birth rates and related demographic characteristics, such as maternal ...age and the level of education of parents in South Korea from 1981 to 2019. This study analyzed birth data obtained from the Korean Statistical Information Service. From 1981 to 2019, the total twinning rate increased from 5 to 22.5 pairs per 1000 births. This rapid increase was due to an increase in dizygotic twin births, which mainly occurred in mothers aged between 30 and 39 years. The average maternal age of multiples increased from 26.06 years in 1981 to 33.98 years in 2019, suggesting that a delay in childbearing contributed to the increase in the twinning rate. The percentage of mothers of multiples who completed a college or higher degree (CHD) increased by 1000% from 1981 to 2019, indicating that a sharp increase in the level of education of females in part explains the delay in childbearing. The percentages of individuals who completed a CHD were higher among parents of multiples than among those of singletons in recent years when public funding arrangements for fertility treatments were available. This result suggested that completion of higher education may be associated with increased use of assisted reproductive technology (ART) independent of the financial status of couples. Taken together, the analysis suggested that increased maternal age, ART and the increased number of females who completed CHD may be responsible for the remarkable increase in the rates of multiple births in South Korea in the last four decades.
Twin studies of physical exercise for Asian twins are sparse. This study aimed to examine genetic and environmental influences on frequency of vigorous exercise (FVE) in South Korean twins, with a ...special emphasis on sex effects. Telephone interviews on FVE were administered to 1757 twins (mean age = 19.05 years, SD = 3.01 years). Tetrachoric correlations were significantly different between monozygotic (MZ) and dizygotic (DZ) twins in males (.40 vs. .12), but they were similar in females (.44 vs. .45), suggesting the importance of genetic factors in FVE in males and that of common environmental factors in females. A scalar sex-limitation model incorporating age as a modifier was applied to data. The results revealed that genetic, common and individual environmental influences did not vary significantly with age, but differed across two sexes, confirming twin correlational analyses. In the best-fitting model, additive genetic and individual environmental influences on FVE were, respectively, .35 (95% CI .26, .39) and .65 (95% CI .61, .74) in males, and common and individual environmental influences were, respectively, .45 (95% CI .35, .53) and .55 (95% CI .47, .65) in females. These results contrasted starkly with recent findings from a large sample of Chinese adult twins (age >18 years), in which most variance (≥95%) of vigorous physical activity was attributable to common environmental influences in both sexes. Replications in other Asian samples are clearly needed.
The present study aimed to explore secular trends in age at voice change (AVC), estimate heritability of AVC and investigate to what extent common genes influence the association between AVC and body ...mass index (BMI) in South Korean males. The sample of 955 male twins consisted of 241 pairs and 118 co-twin missing monozygotic (MZ) twins, 82 pairs and 50 co-twin missing dizygotic (DZ) twins and 141 male members of opposite-sex DZ twins who participated in telephone surveys in the South Korean Twin Registry. AVC was asked of twins during the surveys. The mean (SD) age of the sample was 18.92 (2.42) years (range: 16.00–29.25 years). The birth years of the twins were divided into two groups (1988–1993, 1994–2001). Kaplan–Meyer survival analyses were conducted to compute the mean age of AVC in the total sample as well as to test mean differences between the two birth cohorts. Maximum likelihood twin correlations and univariate and bivariate model-fitting analyses were performed. The mean AVC in the total sample was 14.19 (95% CI 14.09, 14.29) years. The mean AVC significantly declined from 14.38 to 14.02 years from 1988 to 2001, confirming downward trends in AVC in recent years. Heritability for AVC was .59 (95% CI .50, .67), which was within the range reported in most Western twin studies. Although the phenotypic correlation between AVC and BMI was modest (r = −.14; 95% CI −.07, −.21), it was entirely mediated by common genes, similar to what has been found in females in prior twin studies. In conclusion, the present twin study underscores the importance of genetic influences on pubertal timing and its association with BMI in South Korean males.
Twins reared apart are rare, especially twins raised in different countries and cultures. This report documents the behavioral, physical, and medical similarities and differences of monozygotic ...female cotwins, raised separately by an adoptive family in the United States and the biological family in South Korea. Similarities were evident in personality, self-esteem, mental health, job satisfaction and medical life history, consistent with genetic influence found by the Minnesota Study of Twins Reared Apart and related studies. An overall twin correlation across thirty-eight measures was r = 0.95, p < .001. In contrast with previous research, the twins' general intelligence and non-verbal reasoning scores showed some marked differences. Adding these cases to the psychological literature enhances understanding of genetic, cultural, and environmental influences on human development.
The relationship between prosocial behavior (PB) and cognitive abilities has been well documented. This study explored genetic and environmental overlaps in the relationship between PB and verbal and ...non-verbal abilities. Participants included 3179 twins attending public secondary schools in Lagos State in Nigeria (mean age = 14.6 years, SD = 1.7 years). The PB scale of the Strengths and Difficulties Questionnaire was used to measure PB. The set B of the Mill-Hill Vocabulary test (MHV) and Raven's Standard Progressive Matrices Plus (SPM) were used to measure verbal and non-verbal ability, respectively. The MHV-PB and the SPM-PB correlations were 0.29 (95%CI = 0.26, 0.32) and 0.19 (95%CI = 0.15, 0.23), respectively, indicating that PB is more strongly related to verbal than to non-verbal ability at the phenotypic level. Bivariate model-fitting analyses revealed that additive genetic correlations were 0.73 (95%CI = 0.59, 0.92) for MHV-PB and 0.55 (95%CI = 0.40, 0.82) for SPM-PB, respectively. Neither shared nor non-shared environmental correlations were significant. Bivariate heritability was estimated at 1.0 (95%CI = 0.65, 1.00 for MHV- PB and 95%CI = 0.60, 1.00 for SPM-PB), indicating that the relationships between PB and two cognitive measures were mediated entirely by common genes. Multivariate Cholesky model-fitting analysis showed that while MHV explained 10% of additional additive genetic variance of PB above and beyond the common genetic variance, SPM became non-significant after the common genetic variance was controlled. These results suggested that the relationship between cognitive abilities and PB may be largely driven by verbal ability.
•Cognitive tests and prosocial behavior (PB) scales were given to Nigerian twins.•PB was more strongly correlated with verbal than with non-verbal ability.•The associations between cognitive tests and PB were due entirely to common genes.•Verbal ability explained genetic variance of PB above and beyond non-verbal ability.
Gene-environment correlations and interactions for the relationship between emotional problems (EP) and family environment in adolescents in low- to middle-income countries (LMIC) have been rarely ...investigated. In total, 3207 adolescent twins aged 12-18 (Mean = 14.6 ± 1.73) years attending public schools in Lagos State in Nigeria completed measures of EP and Family Chaos (FC). Model-fitting analyses suggested that genetic and non-shared environmental influences on EP were 21% and 71%, respectively, and the corresponding estimates were 23% and 71% for FC. Shared environmental influences were not significant (8% and 6% respectively). Phenotypic correlation between EP and FC was .30 (95% CI = .27-.34), which was significantly influenced by genetic (A - 49%, 95% CI: 0.01-0.97) and non-shared environmental factors (E - 32%, 95% CI: 0.10-0.54). Shared environmental influences were not significant (C - 19%, 95% CI: -0.13 to 0.50). Moderation effects were significant whereby as FC increased, A on EP decreased (βA = -0.07, 95% CI: -0.12 to -0.02) while E increased (βE = 0.06, 95% CI: 0.03-0.09). Our findings indicate that genetic and non-shared environmental risk factors may mediate the relationship between EP and FC, and that as FC increases, protective genetic influences on EP may be attenuated, whereas environmental influences may become stronger in adolescents in LMIC.
Heritability of age at menarche (AAM) in African populations remains largely unknown. A question on AAM was given to 1803 454 monozygotic (MZ), 823 same-sex dizygotic (DZ), and 526 female members of ...opposite sex adolescent twins attending public schools in Lagos State, Nigeria. The age range of the sample was 12–18 years, with a mean (SD) of 14.57 (±1.70) years. The data included 905 missing cases consisting of those who had not experienced menarche and did not recall AAM. Missing values were imputed using the Expectation-Maximization algorithm. Kaplan–Meier analysis based on the imputed data yielded 13.23 years 95% CI 13.18, 13.28 for the mean and 13.00 years 95% CI 12.96, 13.04 for the median of AAM. Twin correlation and model-fitting analyses were performed on the basis of those who reported AAM (MZ = 82 complete pairs and 38 cotwin missing cases; DZ = 157 complete pairs and 99 cotwin missing cases). Maximum likelihood MZ and DZ twin correlations for AAM were .63 (95% CI .48, .74) and .33 (95% CI .19, .45) respectively. Model-fitting analyses indicated that 58% (95% CI 46, 67) of the variance of AAM was associated with additive genetic influences with the remaining variance, 42% (33−54) being due to nonshared environmental influences including measurement error. The heritability estimate found in this study was within the range of those found in Asian and Western twin samples.
Familial twinning and fertility traits were investigated in Nigerian mothers of dizygotic (DZ) twins (MoDZT; N = 972) and controls (N = 525) who responded to our person-to-person interview, which ...included questions on pregnancy history and family history of DZ twinning. Controls were defined as women who are not twins themselves and do not have twins in their first-degree relatives. Over 95% of the participants were Yoruba. We found that Nigerian MoDZT had an average of 4.0 (±2.6) pairs of twins among their relatives, and of these, the prevalence of DZ twins was significantly higher than that of monozygotic (MZ) twins (45.9% vs. 25.8%). Controls had an average of 0.5 (±0.4) pairs, and over 95% of the controls had no twins in their relatives. These results suggest genetic influences on DZ twinning in Nigerians. MoDZT were significantly younger in their mean age at first child, and had higher parity than controls, suggesting increased fertility in MoDZT. As compared to mothers with a single set of twins, mothers (N = 130) with multiple sets had significantly more twins among their relatives (5.4 pairs vs. 3.7 pairs) and had their first twins at a younger age (28.4 vs. 30.7 years), indicating that mothers with multiple sets of twins might have higher genetic propensity for twinning associated with earlier age at twin pregnancy. Our findings argue for genomewide association studies for DZ twinning in Nigerians, and may help to develop intervention strategies to overcome infertility/subfertility problems.
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