Social learning theory postulates that self-efficacy is learned through the person's interaction with his/her physical and social environment. In this genetically informative, population-based, multi-informant study of 1,394 adolescent twin pairs, self-efficacy was modeled as one latent psychometric self-efficacy factor with genetic and environmental effects common to all informants, as well as for effects specific for each informant. The results showed that 75% of variation in self-efficacy was due to genetic factors. Non-shared environmental causes explained the remaining 25% of the variance in the latent factor, with no effect of common environment. Some informant-specific effects were also found. The present study challenges the theoretical assumption of learning as the dominant etiological factor behind self-efficacy in young people.

Context: The detection and replication of genes involved in psychiatric outcome has been notoriously difficult. Phenotypic measurement has been offered as one explanation, although most of this discussion has focused on problems with binary diagnoses. Objective: This article focuses on two additional components of phenotypic measurement that deserve further consideration in evaluating genetic associations: (1) the measure used to reflect the outcome of interest, and (2) the developmental stage of the study population. We focus our discussion of these issues around the construct of impulsivity and externalizing disorders, and the association of these measures with a specific gene, GABRA2. Design, Setting, and Participants: Data were analyzed from the Collaborative Study on the Genetics of Alcoholism Phase IV assessment of adolescents and young adults (ages 12–26; N = 2,128). Main Outcome Measures: Alcohol dependence, illicit drug dependence, childhood conduct disorder, and adult antisocial personality disorder symptoms were measured by psychiatric interview; Achenbach youth/adult self-report externalizing scale; Zuckerman Sensation-Seeking scale; Barratt Impulsivity scale; NEO extraversion and consciousness. Results: GABRA2 was associated with subclinical levels of externalizing behavior as measured by the Achenbach in both the adolescent and young adult samples. Contrary to previous associations in adult samples, it was not associated with clinical-level DSM symptom counts of any externalizing disorders in these younger samples. There was also association with sensation-seeking and extraversion, but only in the adolescent sample. There was no association with the Barratt impulsivity scale or conscientiousness. Conclusions: Our results suggest that the pathway by which GABRA2 initially confers risk for eventual alcohol problems begins with a predisposition to sensation-seeking early in adolescence. The findings support the heterogeneous nature of impulsivity and demonstrate that both the measure used to assess a construct of interest and the age of the participants can have profound implications for the detection of genetic associations.

Aim: The present study aims to estimate the relative importance of genetic and environmental factors for health-related quality of life (HRQL) measured by the 12-item Short-Form Health Survey (SF-12). Methods: The study was based on two Danish twin cohorts (46,417 twin individuals) originating from the nationwide, population-based Danish Twin Registry. The twins were approached by a mailed-out questionnaire in 2002. The questionnaire included the SF-12, information on demographic factors, and questions on a variety of specific diseases. Heritability of the SF-12 includes the physical component summary (PCS) and the mental component summary (MCS); and etiologically important variance components were estimated using multivariate biometric models. The respondents were stratified into six groups, based on age and sex. Results: A total of 33,794 (73%) individual twins responded to the survey. The SF-12 was completed by 29,619 individuals, which included 9,120 complete twin pairs. Overall, the best-fitting model explaining the variance of HRQL was the ACE model. The estimated heritability of the SF-12 was between 11% and 35%, whereas between 65% and 89% could be explained by unique environmental or stochastic factors in the different sex and age groups. The highest heritability was seen among older twins. In addition, the genetic correlation between MCS and PCS scores was low (0.07 and 0.23 for males and females, respectively) among younger and high (0.26 and 0.45 for males and females, respectively) in the oldest age group. Both the largest genetic influence on HRQL and the largest genetic overlap between the scores were seen in the oldest age group, which consisted of twins older than 55. The unique environmental correlation between MCS and PCS were generally negative. Conclusion: The heritability of HRQL differs between different age groups. In general, most of the variance in the SF-12 summary components was determined by unique environmental factors.

Teenage motherhood is associated with poor offspring outcomes but these associations may be influenced by offspring birth year because of substantial social changes in recent decades. Existing research also has not examined whether these associations are due to the specific effect of mother's age at childbirth or factors shared by siblings in a family. We used a population-based cohort study in Sweden comprising all children born from 1960 to 1989 (N = 3,162,239), and a subsample of siblings differentially exposed to maternal teenage childbearing (N = 485,259) to address these limitations. We examined the effect of teenage childbearing on offspring violent and non-violent criminal convictions, poor academic performance, and substance-related problems. Population-wide teenage childbearing was associated with offspring criminal convictions, poor academic performance, and substance-related problems. The magnitude of these associations increased over time. Comparisons of differentially exposed siblings indicated no within-family association between teenage childbearing and offspring violent and non-violent criminal convictions or poor academic performance, although offspring born to teenage mothers were more likely to experience substance-related problems than their later-born siblings. Being born to a teenage mother in Sweden has become increasingly associated with negative outcomes across time, but the nature of this association may differ by outcome. Teenage childbearing may be associated with offspring violent and non-violent criminal convictions and poor academic performance because of shared familial risk factors, but may be causally associated with offspring substance-related problems. The findings suggest that interventions to improve offspring outcomes should delay teenage childbearing and also target risk factors influencing all offspring of teenage mothers.

The present study is the first to assess phenotypic correlations between alexithymia and the Dark Triad traits of personality in a community sample, as well as the common genetic and environmental factors underlying these correlations. Participants were 232 North American adult twin pairs who completed the Narcissistic Personality Inventory, the Self-Report Psychopathy Scale, the MACH-IV, and the Toronto Alexithymia Scale. Results revealed that alexithymia correlates significantly and positively with psychopathy and Machiavellianism, and negatively with narcissism. Subsequent bivariate behavioral genetic analysis demonstrated that these phenotypic correlations were primarily attributable to common genetic and common non-shared environmental factors. The implication of these findings regarding the maladaptive functions of alexithymia within the antisocial realm of behavior and the need for replication are discussed.

Non-shared parenting and deviant peer affiliation are linked to differences in externalizing behaviors between twins. However, few studies have examined these two non-shared environments simultaneously. The present study examined the transactional roles of differential parenting (i.e., warmth and hostility) and deviant peer affiliation on monozygotic (MZ) twin differences in externalizing behaviors using a two-wave longitudinal study of twins and their parents. The sample consisted of 520 pairs of MZ twins (46.5% males, 53.5% females), with a mean age of 13.86 years (SD = 2.10) at the T1 assessment, residing in Beijing, China. The association between non-shared hostility in parenting and adolescent externalizing behaviors was mainly explained by a child-driven effect whereby the twin with a higher level of externalizing behaviors than his or her co-twin was more likely to receive more hostility from the parents. Similarly, the relationship between deviant peer affiliation and adolescent externalizing behaviors supported the selection effect whereby the twin with a higher level of externalizing behaviors than his or her co-twin was more likely to affiliate with deviant peers. The theoretical and practical implications of these findings are discussed.

Children born with non-optimal birth characteristics — that is, are small for gestational age and/or preterm — have an increased risk for several long-term effects such as neurological sequelae and chronic disease. The purpose of this study was to examine whether twins exhibited a different outcome, compared with singletons, in terms of hospitalization during adolescence and early adulthood, and to what extent differences remain when considering the divergence in birth characteristics between singletons and twins. Persons born between 1973 and 1983 in Sweden and surviving until age 13 were included and followed until the end of 2006. Data on birth characteristics, parental socio-demographic factors, and hospitalizations were collected from national registers. Adjusting for parental socio-demographic factors, twins had a higher risk of being hospitalized than singletons (odds ratio, OR = 1.17, 95% confidence interval, CI = 1.10–1.25) and more often due to ‘Congenital anomalies’ (OR = 1.18, 95% CI = 1.06–1.28), ‘Infections’ (OR = 1.14; 95% CI = 1.08–1.20), ‘External causes of illness’ (OR = 1.10, 95% CI = 1.06–1.15), and ‘Diseases of the nervous system’ (OR = 1.18, 95% CI = 1.10–1.26). Stratifying for birth characteristics, this difference diminishes, and for some diagnoses non-optimal twins seem to do slightly better than non-optimal singletons. Thus, twins with non-optimal birth characteristics had a lower risk of hospitalization than non-optimal singletons on, for example, ‘Congenital anomalies’ and ‘Diseases of the nervous system’ (OR = 0.86, 95% CI = 0.77–0.96; OR = 0.88, 95% CI = 0.81–0.97, respectively) and Total (any) hospitalization (OR = 0.87, 95% CI = 0.83–0.92). Among those with optimal birth characteristics, twins had an increased hospitalization due to ‘External causes of illness’ (OR = 1.07, 95% CI = 1.02–1.13) compared with optimal singletons. Twins have higher hospitalization rates than singletons. In stratifying for birth characteristics, this difference diminishes, and for some diagnoses, non-optimal twins seem to do less poorly than non-optimal singletons.

Twin–twin transfusion syndrome (TTTS) is an antenatal complication of monochorionic multiple gestations. There have been few studies exploring the role of laser photocoagulation or outcomes following treatment in monochorionic triplet pregnancies with TTTS. We present a case where TTTS and twin anemia–polycythemia sequence (TAPS) complicated a monochorionic triplet pregnancy. Following the laser photocoagulation to treat the TTTS between the triplets, an intra-uterine death occurred in one triplet and TAPS developed in the remaining two triplets. Intervention in this case resulted in a 2-week prolongation of pregnancy and a positive outcome for the remaining fetuses. This case and other published data reviewed in this article suggest that laser photocoagulation has a potential role for TTTS in monochorionic triplet pregnancies.

Background and objective: Intrauterine growth restriction (IUGR) may be associated with significantly higher aortic intima–media thickening (aIMT) values. It is unknown if fetal aIMT is associated with glomerulosclerosis and amniotic albuminuria in utero. Design, setting, participants, and measurements: Fetal abdominal aIMT and amniotic albumin/creatinine ratio (ACR) were measured in 126 individual twin fetuses, recruited by the Obstetrics and Gynaecology Clinics of the University of Padua (Italy) Medical Center. The IUGR twin fetuses were classified into two groups: Group A were those fetuses whose estimated fetal weight (EFW) was <10th percentile with pulsatility index >2 SD and Group B were those fetuses whose EFW was <10th percentile and had no velocimetry abnormalities. Results: The median fetal aIMT was significantly different in the three groups (Group A = 0.9 mm; Group B = 0.7 mm; and appropriate for gestational age (AGA) = 0.5 mm; p < .0001). It was significantly higher in Group A than in the AGA group (p < .0001) and than in the Group B fetuses (p = .003), respectively. In addition, ACR was different in the three groups (Group A = 183,500 mg/g; Group B = 6,4720 mg/g; and AGA = 8,2750 mg/g; p = .0002). It was significantly higher in Group A than in the AGA group (p = .03) and than in Group B (p = .02), respectively. Conclusions: Growth-restricted twin fetuses with velocimetry abnormalities present are associated with aIMT and higher ACR levels in amniotic fluid, which could be possible markers in utero of preclinical atherosclerosis, and early glomerulosclerosis.

Objective: To evaluate the perinatal outcome of intrauterine growth-restricted preterm twins and contribution of prematurity to morbidity and mortality. Study design: A case–control study of 211 preterm twins: 108 growth-restricted twins matched with 103 normal growth twins of the same gestational age. Mortality and morbidity rates were compared between groups. Result: Fetal and overall perinatal mortality rates of growth-restricted fetuses were higher than normal growth ones. Respiratory distress syndrome incidence was lower and neurologic sequelae incidence higher in growth-restricted twins. No differences were observed between groups with respect to neonatal mortality, low Apgar score, neonatal intensive care unit admission, periventricular hemorrhage, sepsis, jaundice, and hematologic or metabolic disorders. Conclusion: Adverse perinatal outcomes of preterm twins complicated with intrauterine growth restriction are represented by a higher antepartum mortality rate, but once born alive, neonatal outcomes seem to be associated only with gestational age at birth, excluding a protective effect on lung maturation and a higher risk of long-term neurologic sequelae.

Adiponectin has been associated with insulin resistance and type 2 diabetes mellitus and possibly fetal growth. Our aim was to assess the association between the single nucleotide polymorphisms (SNPs) of the adiponectin gene (ADIPOQ) and the birth sizes. We investigated four SNPs of ADIPOQ (rs182052, rs2241766, rs1501299, and rs266729) and birth height and weight in 237 healthy full-term neonates. The neonates with the rs182052 G allele had a greater birth weight (p = .043 in the dominant model) and a higher ponderal index (p = .028 in the additive model). The rs2241766 G allele was associated with a greater birth weight (p = .016 in the recessive model). In a logistic regression analysis, the homozygotes for the rs182052 G allele and those for the rs2241766 G allele showed a significant association with a greater birth weight above 90 percentile (OR 2.75, 95% CI 1.13–6.70 and OR 5.15, 95% CI 1.66–15.99, respectively). In conclusion, we found an association between rs182052 and rs2241766 and birth weight and ponderal index among healthy neonates and suggested that adiponectin might have some roles in fetal growth.

Numerous papers have investigated the distribution of birth weight. This interest arises from the association between birth weight and the future health condition of the child. Birth weight distribution commonly differs slightly from the Gaussian distribution. The distribution is typically split into two components: a predominant Gaussian distribution and an unspecified ‘residual’ distribution. In this study, we consider birth weight data from the Åland Islands (Finland) for the period 1885–1998. We compare birth weight between males and females and among singletons and twins. Our study confirms that, on average, birth weight was highest among singletons, medium among twins, and lowest among triplets. A marked difference in the mean birth weight between singleton males and females was found. For singletons, the distribution of birth weight differed significantly from the normal distribution, but for twins the normal distribution held.

The purpose of the present study was to clarify the characteristics of fatal child maltreatment in families with multiple births in Japan. An exhaustive information search was performed to find multiple-birth cases between July 2003 and March 2011. There were 437 cases of fatal maltreatment of children aged 0–17 years during this period, including 14 involving multiple-birth children. A keyword search was performed to create a full profile for each multiple-birth case. The 14 multiple-birth victims were twins from 13 families. No significant difference between twins and singletons with fatal maltreatment was observed for most characteristics. However, in the case of twins, 0-month victims were rare, and the number of children per family was larger. One twin died from shaken baby syndrome. The victim's siblings were also maltreated in six out of 12 relevant cases, including all six co-twins. Premature birth, having a disabled co-twin, delay of growth or development, and parental disfavor tended to be factors of maltreatment when only one twin was maltreated. Four families were given suspended sentences in total, including three mothers who acted as solitary murderers (43% = 3/7). In conclusion, recent Japanese nationwide data suggests that the non-specific overburden of child rearing might be one possible reason for higher frequency of child maltreatment for multiples compared with singletons, and parental comparisons between two twins might be another. The penal sentences for fatal child maltreatment might be more lenient for perpetrators of this crime against twins than against singletons.

The twin children who survived the Holocaust and the horrific medical experiments conducted by Nazi doctors are sometimes overlooked in the relevant literature. This topic and more were discussed as part of an annual conference hosted by students from Yeshiva University's Medical Ethics Society in October 2012. A selective summary of this meeting is followed by summaries of recent twin studies concerning genetic influences on twinning, in vitro fertilization versus spontaneous twin pregnancies, gender identity disorder, and royal support for twin registries. Several human interest stories are also worth noting. They include identical twin school principals, twin loss at Sandy Hook Elementary School, timely twin documentaries, new twin and twin-like reunions, and the passing of two prominent twins.