The Dark Triad of personality, comprising Machiavellianism, narcissism, and psychopathy, was investigated in relation to the Supernumerary Personality Inventory (SPI) traits, because both sets of variables are predominantly distinct from the Big Five model of personality. Correlational and principal factor analyses were conducted to assess the relations between the Dark Triad and SPI traits. Multivariate behavioral genetic model-fitting analyses were also conducted to determine the correlated genetic and/or environmental underpinnings of the observed phenotypic correlations. Participants were 358 monozygotic and 98 same-sex dizygotic adult twin pairs from North America. As predicted, results revealed significant correlations between the Dark Triad and most SPI traits, and these correlations were primarily attributable to common genetic and non-shared environmental factors, except in the case of Machiavellianism, where shared environmental effects emerged. Three correlated factors were extracted during joint factor analysis of the Dark Triad and SPI traits, as well as a heritable general factor of personality — results that clarified the structure of the Dark Triad construct. It is concluded that the Dark Triad represents an exploitative and antisocial construct that extends beyond the Big Five model and shares a theoretical space with the SPI traits.

Background: The normal development of cortisol regulation during childhood is thought to be influenced by a complex interplay between environmental and genetic factors. Method: The aim of this study was to estimate genetic and environmental influences on basal cortisol levels in a sample of 151 twin pairs aged 9–16 years. Salivary cortisol was collected on two consecutive days when the children attended school — immediately after awakening, 30 min post-awakening and at bedtime. Results: Heritability was highest (60%) for cortisol levels about 30 min after awakening. For samples taken immediately at awakening heritability was less pronounced (28%) and in the evening low (8%). Conclusion: The limited genetic influence on evening levels, moderate on cortisol at awakening and high on awakening response, might imply two genetic regulation patterns, one specifically for awakening response and one for the circadian rhythm proper. These findings could explain divergent results in previous studies and highlight the importance of taking the circadian rhythm into account in studies of cortisol levels in children.

Telegenetics is a new development in the service delivery of Genetic Services in Australia. This project was designed to establish if it was an acceptable alternative to a face-to-face consultation in the genetic assessment of intellectual disability, including morphological assessment, of the patient. Ten children from two outreach clinics in rural NSW who were referred by their pediatrician were assessed by a single geneticist via telehealth and then seen again face-to-face as a ‘gold standard'. Satisfaction surveys were then sent to both the parents and the referring pediatricians. After the face-to-face appointment, the clinical geneticist reviewed the recordings of both the transmitted footage and the high definition footage that was sent separately. There were very few morphological findings missed by the telegenetic assessments. The discrepancies that were noted could decrease in frequency as staff become more familiar with the methods. The parents of the patients reported no problem with the cameras and telehealth. They would have preferred face-to-face appointment but would be happy to have the telehealth appointment if it meant being seen earlier. This pilot study suggests that clinical genetic diagnostic assessment could be performed by telemedicine.

We explored heritabilities of the State and Trait Anxiety Inventory (STAI) and the Alcohol Use Disorders Identification Test (AUDIT), and associations including genetic and environmental correlations between the phenotypes among Korean twins and their families. We analyzed the data of 1,748 participants (835 men, 913 women, 656 individuals of monozygotic twins, 173 individuals of same-sexed dizygotic twins, 919 non-twin family members, age 30–79 years) from the Healthy Twin study. Heritabilities and bivariate analyses were assessed using the SOLAR package software. In the methods of generalized estimation equations, women in the 4th quartile of state and trait scores were 17% and 15%, respectively more likely to be hazardous alcohol users compared to women in the lower three quartiles (P < .05). However, there were no significant associations between these phenotypes in men. After adjusting for age and squared age, the heritability estimates were 0.26 in men and 0.34 in women for the state score; for the trait score, 0.35 in men and 0.31 in women; for the AUDIT score, 0.32 in men and 0.37 in women (P < .001). After adjusting for age and squared age, there was a significant genetic correlation between the trait score and the AUDIT score, and a significant non-genetic correlation between the state score and the AUDIT score in women, while there were no significant genetic or non-genetic correlations between these phenotypes in men. The STAI and AUDIT scores are heritable in Koreans and the relationships between these phenotypes may be inconsistent by sex.

Twin studies suggest that global and regional brain volumes are highly heritable. However, estimates of heritability vary across development. Given that all twin studies are open to the potential criticism of non-generalizability due to differences in intrauterine environment between twins and singletons, these age effects may reflect the influence of perinatal environmental factors, which are unique to twins and which may be especially evident early in life. To address this question, we compared brain volumes and the relationship of brain volumes to gestational age in 136 singletons (67 male, 69 female) and 154 twins (75 male, 79 female; 82 DZ, 72 MZ) who had received high resolution MRI scans of the brain in the first month of life. Intracranial volume, total white matter, and ventricle volumes did not differ between twins and singletons. However, cerebrospinal fluid and frontal white matter volume was greater in twins compared to singletons. While gray matter volumes at MRI did not differ between groups, the slope of the relationship between total and cortical gray matter and gestational age at the MRI scan was steeper in MZ twins compared to DZ twins. Post-hoc analyses suggested that gray matter development is delayed in MZ twins in utero and that they experience ‘catch-up’ growth in the first month of life. These differences should be taken into account when interpreting and designing studies in the early postnatal period.

Molecular genetic research has provided some evidence for the association between depression and metabolic disorders. We sought to determine if molecular findings are reflected in twin analyses testing if common genetic and environmental risk factors contribute to the co-occurrence of diabetes and depression. Data to derive depression and diabetes were collected from 1,237 male-male twins who participated in the 2005 Vietnam Era Twin Study of Aging (VETSA). The 1,237 twins were comprised of 347 MZ pairs, 3 MZ singletons, 267 DZ pairs and 6 unpaired twins. Depression was defined as a score below 46 on the Short Form-36 mental component summary score. Diabetes was defined by self report, use of anti-diabetic medications and insulin. Twin models were fit to estimate the correlation of genetic and environmental contributions to depression and diabetes. Consistent with other studies these data support the association between depression and diabetes (OR = 1.7; 95%CI: 1.1–2.7). Genetic vulnerability accounted for 50% (95%CI: 32%–65%) of the variance in risk for depression and 69% (95%CI: 52%–81%) of the variance in risk for diabetes. The genetic correlation between depression and diabetes was r = 0.19 (95%CI: 0–0.46) and the non-shared environmental correlation was r = 0.09 (95% CI: 0–0.45). Overall there is little evidence that common genetic and environmental factors account for the co-occurrence of depression and diabetes in middle aged men. Further research in female twins and larger cohorts is warranted.

In the mammary gland, Wnt signals are strongly implicated in initial development of the mammary rudiments and in the ductal branching and alveolar morphogenesis that occurs during pregnancy. Previously, we identified two Wnt signaling pathway-implicated genes, PPP3CA and MARK4, as having a role in more aggressive and potentially metastatic breast tumors. In this study, we examined two SNPs within PPP3CA and MARK4 in an Australian case-control study population for a potential role in human breast cancers. 182 cases and 180 controls were successfully genotyped for the PPP3CA SNP (rs2850328) and 182 cases and 177 controls were successfully genotyped for the MARK4 SNP (rs2395) using High Resolution Melt (HRM) analysis. Genotypes of randomly selected samples for both SNPs were validated by dye terminator sequencing. Chi-square tests were performed to determine any significant differences in the genotype and allele frequencies between the cases and controls. Chi-square analysis showed no statistically significant difference (ρ > .05) for genotype frequencies between cases and controls for rs2850328 (χ2 = 1.2, p = .5476) or rs2395 (χ2 = .3, p = .8608). Similarly, no statistical difference was observed for allele frequencies for rs2850328 (χ2 = .68, p = .4108) or rs2395 (χ2 = .02, p = .893). Even though an association of the polymorphisms rs2850328 and rs2395 and breast cancer was not detected in our case-control study population, other variants within the PPP3CA and MARK4 genes may still be associated with breast cancer, as both genes are implicated with processes involved in the disease as well as their mutual partaking in the Wnt signaling pathway.

Sex differences in mental rotation ability have been observed in many countries. A previous study of Finnish participants reported that genetic and environmental influences on mental rotation ability differ between sexes. In this study, we assessed genetic and environmental influences on variance in mental rotation ability in 649 Japanese twins using a mental rotation test. To explain the influence of sex on variance in mental rotation ability, we applied genetic analysis using the sex limitation model. The following two factors explained variance in mental rotation ability: (1) the additive genetic factor, which reflects the accumulated small influence of many genes, and (2) the unique environmental factor, which is a type of environmental factor that differs between co-twins. The shared environmental factor, a type of environmental factor common for co-twins, could not explain the variance in mental rotation ability. Furthermore, the additive genetic factor was the same between sexes (i.e., not qualitative sex differences for the additive genetic factor), indicating that the same genes affect mental rotation ability in both sexes. Despite this observation, the additive genetic influence was greater in males than in females. In contrast, the unique environmental influence was not different between sexes. Considering the current results and those of a previous study, the quantitative sex difference for the additive genetic influences in mental rotation ability may be universal, while the unique environmental differences may depend on the characteristics of specific populations.

Background: There is currently little evidence concerning the impact of the inter-twin relationship on behavioral outcomes and yet the twin relationship is frequently hypothesized to be a unique source of psychopathology in twins. The current study asked whether the inter-twin relationship is a predictor of behavioral difficulties and whether there are zygosity differences in this relationship.

Method: An Australian sample of same sex twins (N = 356, 164 MZ and 192 DZ) was studied in the year prior to school (Time 1) and again in first year of school (Time 2). Associations between twin-relationship and behavior problems were examined via path-analysis, and Satorra-Bentler chi-square difference tests were used to compare twins across zygosity.

Results: Results show that both conflict and lower levels of warmth at Time 1 were predictive of hyperactivity and conduct disorder at Time 2, but they were not associated with emotional difficulties or peer problems. While DZ twins shared less warmth than MZ twins, there were no differences in behavior problems.

Conclusion: Conflict and lower levels of warmth in the inter-twin relationship are associated with hyperactivity and conduct disorder and may serve as important considerations when making decisions regarding class separation at entry to school.

This study aimed to: (1) determine concordance rates of self-reported and subjectively determined indicators of oral malodor in twins; (2) determine the relative contributions of genetic and environmental factors to levels of volatile sulfur compounds (VSCs) in intraoral and exhaled breath. Fifty-one twin pairs participated in the study. Measurements of VSCs were obtained by a halimeter. The presence of tongue coatings was determined and twins filled out a 32-item questionnaire on oral malodor indicators independently of one another. Estimates of heritability (h2) for halimeter measurements were computed by SOLAR. The concordance rates for the presence of tongue coating among identical and fraternal twins were 67% and 11%, respectively. In the 10 most informative items, 70% exhibited higher concordance rates for identical than for fraternal twins. Of particular interest were the differences in concordance rates for dry mouth, sinus infection and unusual sweating. The h2 for intra-oral breath was 0.28 ± 0.17 (NS), whereas the h2 for exhaled breath was 0.50 ± 0.20 (p = .0207). The concordance rates of tongue coatings and malodor indicators were higher in identical twins than in fraternal twins. Intraoral breath VSC values were primarily attributable to environmental factors, whereas exhaled breath VSC values were partially explained by genetic factors.

Absolute pitch is a rare pitch-naming ability with unknown etiology. Some scientists maintain that its manifestation depends solely on environmental factors, while others suggest that genetic factors contribute to it. We sought to further investigate the hypothesis that genetic factors support the acquisition of absolute pitch and to better elucidate the inheritance pattern of this trait. To this end, we conducted a twin study and a segregation analysis using data collected from a large population of absolute pitch possessors. The casewise concordance rate of 14 monozygotic twin pairs, 78.6%, was significantly different from that of 31 dizygotic twin pairs, 45.2%, assuming single ascertainment (x2 = 5.57, 1 df, p = .018), supporting a role for genetics in the development of absolute pitch. Segregation analysis of 1463 families, assuming single ascertainment, produced a segregation ratio pD = .089 with SEpD = 0.006. Unlike an earlier segregation analysis on a small number of absolute pitch probands from musically educated families, our study indicates that absolute pitch is not inherited in a simple Mendelian fashion. Based on these data, absolute pitch is likely genetically heterogeneous, with environmental, epigenetic, and stochastic factors also perhaps contributing to its genesis. These findings are in agreement with the results of our recent linkage analysis.

Being an identical twin does not necessarily mean having identical perceptions of family functioning, nor of the twin relationship. Using the co-twin control design, the aim of this study was to explore perceptions of family dynamics and the twin relationship in monozygotic (MZ) twins discordant and concordant for Developmental Coordination Disorder (DCD). It was hypothesized that, as has been found in twins discordant for cerebral palsy, twins without DCD would perceive family functioning as less healthy than would their co-twins with DCD. It was also hypothesized that the twin relationship would be regarded generally as mutually supportive. Questionnaire data on 866 sets of MZ twins aged 6 to 17 years were used to identify seven sets discordant, and two sets concordant for DCD. Quantitative (General Functioning Scale of the Family Assessment Device — FAD), and qualitative (semi-structured interview) measures were used to assess family dynamics and the twin relationship. In discordant sets, six of seven twins without DCD rated family functioning at a less healthy level than did their co-twins with DCD. All twins in the DCD concordant sets rated their family functioning at a healthy level. From the semi-structured interviews, emergent themes included friendship, support, minimal sibling rivalry, and minor difficulties. It was concluded that, overall, the twin relationship was regarded as close and mutually supportive, with an ambivalent polarity between the best and most difficult aspects of being an identical twin. Implications for research, policy and clinical practice are discussed.

This study compared the anatomical features of the tongue in nine pairs of twins — six monozygotic and three dizygotic. The aim of the project was to determine if tongues, like any other anatomical structure, could be used to reliably predict relatedness given that tongue shape, presentation and surface can be influenced by environment. Using the method of forced choice, 30 subjects were asked to match the photographs of tongues from twins. Our data indicate that, based on visual assessment, monozygotic twins have highly similar tongues (60% matches); similarly, dizygotic twins were matched 31% of the time, which is a higher probability than would be expected from random selection. This study should help identify baseline and control data in future behavioral studies of taste, which has a genetic basis.

Objective: To examine the effect of twin-to-twin delivery time (TTDT) on neonatal outcome. Methods: We evaluated twin deliveries >34 weeks of gestation. Twin pregnancies with both twins delivered by cesarean section and pregnancies with antenatal complications were excluded. We analyzed TTDT and neonatal outcomes of the second twin (umbilical arterial pH value (pHart), Apgar scores at 1, 5 and 10 minutes, need for intensive care). The study population was divided into two homogenous groups based on the mode of delivery: (A) vertex presentation and vaginal delivery of both twins, (B) vertex presentation and vaginal or vaginal operative delivery of twin I, breech or transverse presentation and vaginal breech delivery or cesarean section (CS) of twin II. Results: A total of 207 twin pairs were included in our study. In Group A (n = 151) there were no significant correlations between TTDT and pHart or Apgar scores at 1, 5 and 10 minutes of twin II (p = .156; 0.861; 0.151 and 0.384, respectively). In Group B (n = 56), the mean pHart of twin II was inversely correlated to TTDT, but not significantly (p = .417). TTDT was inversely related to 1-min and 5-min Apgar scores, but not significantly (p = .330; p = .138, respectively). The 10-min Apgar score showed no correlation with TTDT (p = .638). Conclusion: Increasing TTDT was not associated with adverse fetal outcome. Expectant management of the second twin appears possible and elapsed time alone does not appear to be an indication for intervention.

Our objective was to determine the perinatal outcome of first- and second-born twins compared to singletons, born at the same gestational age. To that end we conducted a case-control study in Flanders (Northern Belgium). During a 10-year period (01.01.1999–31.12.2008), the entire twin population — 11,154 first- and 11,118 second-born twins (cases) — was compared to 22,228 singletons (controls) with respect to fetal and neonatal (0–27 days) mortality. Only case and control infants of ≥ 500 grams were included, which explained the unequal number of first- and second-born twins. Mothers and their infants of cases and of controls were derived from the Flemish perinatal database and were matched for maternal age and parity, gestational age and gender of the offspring. The main outcome measures were fetal and neonatal mortality according to gestational age. The frequency of fetal death was statistically significantly less frequent in preterm born twins than in singletons, except at term where the reverse was seen in second-born twins compared to controls. After adjustment for congenital malformations, the results stayed unchanged. Below 28 weeks gestation, singletons had a significantly lower neonatal mortality rate than twins that persisted after adjustment for congenital malformations: the first-born twin versus singleton OR 1.71 (1.17–2.51) and second-born versus singleton OR 2.09 (1.43–3.05). Between 28 and 32 weeks, the second-born twin showed a survival advantage over the control singleton. Between 32 and 36 6/7 weeks both twins had a significantly higher survival rate than the corresponding singleton controls. However, after adjustment for congenital malformations, the aforementioned differences between 28 and 36 6/7 weeks disappeared. When at term, twins and singletons had a comparable, though very low, neonatal death rate. These results confirm previous published data. In conclusion, we demonstrated that the neonatal death rate was lower for twins between 32 and 36 weeks (from 28 weeks for the second born twin) when compared to a singleton of the same gestational age. After adjusting for congenital malformations, there was no statistical significant difference.

Objective: Routine obstetric ultrasound increasingly leads to the detection of structural fetal anomalies. In twin pregnancies with one anomalous twin, counseling on management strategies is complicated. Patients and methods: Twin pregnancies (n = 212) were referred to a tertiary center between January 2007 and July 2009. In a retrospective analysis, twins discordant for a structural fetal anomaly were compared to twins without anomalies in the prenatal ultrasound. Outcome parameters were survival and gestational age at birth. Results: Anomalies were seen in at least one fetus of 30 twin pairs. The two pregnancies in which the anomalies were concordant were terminated. Selective feticide was performed in three cases of major but non-lethal anomalies in dichorionic twins. The remaining 25 cases were managed expectantly. In three of these cases, spontaneous fetal demise of the affected fetus was observed. In five cases with major (lethal) anomalies, the pregnant women and their partners opted for non-intervention comfort care after birth for the affected fetus. Median gestational age at delivery was 257 days for twins without structural anomalies and was 254 days (n = 22) for twins with one anomalous fetus. This was not significantly different (Mann Whitney U, p = .69). Again, no difference was found for median gestational age at delivery in normal vs. discordant anomalous dichorionic twins if subdivided for chorionicity (Mann Whitney U, p = .68). Conclusion: In this cohort we describe the request for expectant management by pregnant women and their partners of those twins discordant for major (lethal) anomalies. Expectant management was not associated with increased risk of premature delivery. Fetocide was only opted for in a small number of cases with severe but non-lethal anomalies in dichorionic twins.

Multiple pregnancies are thought to be associated with a high incidence of perinatal complications such as preterm labor, preeclampsia and low birth weight. But the true mechanisms of these obstetric complications are still uncertain. The components of amniotic fluid reflect the pathophysiology features of the fetus. Amniotic fluid soluble fms-like tyrosine kinase 1(sFLT1), soluble endoglin (sENG), and adiponectin reflect the oxidative stress and pro-inflammatory status and are associated with preeclampsia and fetal growth restriction. We prospectively collected amniotic fluids during amniocentesis from singleton and twin pregnancies. Samples were analyzed for levels of sFLT1, sENG, and adiponectin by enzyme-linked immunosorbent assay. The levels of sENG and sFLT1 were significantly increased in twin pregnancies. Adiponectin was not significantly different between the two groups. These findings would suggest that twin fetuses suffer from more oxidative stress and pro-inflammatory status from the early trimesters.

The purpose of this study was to estimate the number of siblings in each Japanese family with multiple birth children using two sets of census data, from 1990 and 1995. The mean number of siblings for singletons was 2.3 in 1990 (2.4 in 1995), 2.9 (2.9) for one set of twins, 4.6 (4.5) for two sets of twins, and 3.5 (3.3) for one set of triplets. For birth order of multiples, the highest mean sibling number was 4.4 for one set of twins (the middle), 7.5 for two sets of twins (the middle-middle), and 4.3 for one set of triplets (the last). The mean sibling number was slightly higher for like-sexed twins and triplets than in unlike-sexed twins and triplets. The mean sibling number was highest in the Okinawa District, among nine districts (0.4 for singletons, 0.6 for one set of twins, 1.0 for two sets of twins and 0.6 for triplets). The current study of the number of siblings in each family with multiple birth children will help provide data for designing programs to help support multiple-birth families. The method of using census data on multiple births might result in a system to analyze nationwide data on multiple birth children if there is no national registry of multiple births after live births in any country.

The present article explores the social attraction that may evolve on the part of reared apart twins' spouses toward their brothers- and sisters-in-law, that is, their spouses' newly found co-twin. This topic was inspired by the fascinating story of monozygotic reared apart (MZA) twins who were reunited in Perth, Australia in 2008, at age 50. It is followed by brief reviews of twin research articles concerning divorce rates among mothers of multiples and X-chromosome inactivation in MZ female twin pairs. The final section presents informative human interest stories involving twins.