Family and personal protective factors moderate the effects of adversity and negative disposition on smoking among Chinese adolescents.

Tobacco use among Chinese adolescents is increasing at approximately 80,000 new smokers per day. Assessing the causes for initiating tobacco use in China will be important in developing effective interventions and policies to stem rising prevalence rates. This study tested predictors of Resilience Theory in a sample of 602 Chinese adolescents. Results revealed that prior adversity, measured through school and family-related events, was significantly associated with increased smoking in females. Family factors (i.e., family cohesion, family adaptability, parental monitoring) and one personal factor (i.e., academic score) were associated with lower odds for smoking due to prior adversity and negative disposition.

Genetic influence on literacy constructs in kindergarten and first grade: evidence from a diverse twin sample.

Historically, twin research on reading has been conducted on older children and the generalizability of results across racial/ethnic/socioeconomic groups is unclear. To address these gaps, early literacy skills were examined among 1,401 twin pairs in kindergarten and 1,285 twin pairs in first grade (ages 5-7). A multi-group analysis was conducted separately for subsamples defined by neighborhood income while controlling for race/ethnicity within each grade. Substantial additive genetic and shared environmental effects were found for early literacy skills measured in kindergarten. In first grade, variance in early reading was associated with large additive genetic effects for middle and high neighborhood income twins, but shared environmental influence was substantial for low neighborhood income twins. Results suggest that the etiological architecture of some early literacy skills may differ across economic contexts.

Familial associations of rheumatoid arthritis with autoimmune diseases and related conditions.

OBJECTIVE: In the era of genome-wide association studies, familial risks are used to estimate disease heritability and the likelihood of candidate-gene identification. This study was undertaken to estimate associations of rheumatoid arthritis (RA) with any of 33 autoimmune diseases and related conditions among parents and offspring, singleton siblings, twins, and spouses. METHODS: The Multigeneration Register in Sweden was used as a reliable source of information on Swedish families throughout the last century. Data on autoimmune diseases in individual family members were obtained through linkage to the Hospital Discharge Register. The standardized incidence ratio (SIR) was calculated as a measure of the relative risk of RA in family members of patients with RA or any of 33 other autoimmune diseases or related conditions, as compared with the relative risk of RA in those lacking an affected family member. RESULTS: Among a total of 447,704 patients, 47,361 were diagnosed as having RA. The SIRs for RA were 3.02 in offspring of affected parents, 4.64 in siblings, 9.31 in multiplex families, 6.48 in twins, and 1.17 in spouses. Significant associations with the familial risk of RA in offspring according to parental proband were observed for ankylosing spondylitis (SIR 2.96), localized scleroderma (SIR 2.40), Sjögren's syndrome (SIR 2.25), systemic lupus erythematosus (SIR 2.13), systemic sclerosis (SIR 1.65), Hashimoto thyroiditis/hypothyroidism (SIR 1.54), pernicious anemia (SIR 1.53), sarcoidosis (SIR 1.40), psoriasis (SIR 1.36), Wegener's granulomatosis (SIR 1.34), and asthma or polymyalgia rheumatica (SIR 1.32). CONCLUSION: This is the first study to compare the familial risks of RA in relation to a large number of autoimmune diseases and related conditions using data from a single population. The high discordant familial risks in this population suggest that there is extensive genetic sharing between RA and the associated diseases.

Trends in the probability of twins and males in California, 1983-2003.

This study examines the probability of twins by birth year, maternal race-ethnicity, age, and parity and the influences of these demographic factors on the probability of male in twins and singletons in a large, racially diverse population. Recent publications note steep increases in twin births while the probability of male births has been reported to vary by parental race-ethnicity and age and birth order. Probability of male stratified by plurality has not been investigated in California prior to this study. Cubic spline estimates and Poisson regression techniques were employed to describe trends in twins and males using California vital statistics birth and fetal death records over the period from 1983-2003. This study includes 127,787 twin pair and 11,025,106 singleton births. The probability of twins varied by birth year, maternal race-ethnicity, age, and parity. The probability of twins increased by 10.1% from 1983-1992 and increased by 20.1% from 1993-2003, nearly doubling the previous increase. All maternal race-ethnicity groups showed increases in probability of twins with increasing maternal age. Parous women compared to nulliparous women had larger increases in the probability of twins. The probability of males in twins decreased from 1983-1992 and increased from 1993-2003; while in singletons the probability appeared unchanged. These findings show increases in the probability of twins in California from 1983-2003 and identify maternal age, race-ethnicity, and parity groups most likely to conceive twins. The cause of the increase in twins is unknown but coincides with trends towards delayed childbearing and increased use of subfertility treatments.

Twin research, revisionism and metahistory.

We understand metahistory as an approach that studies how histories within a particular discipline have been written and focus on insider scientists' reconstructions of twin research. Using the concept of ethical-political affordances we suggest that such histories are based on a management of resources that prove to be beneficial for representing one's own research traditions in a positive light. Instead of discussing information on the context and intellectual life of pioneers of the twin method, which include high-caliber eugenicists and Nazi ideologues, and on how the twin method has been used and abused, insider scientists' accounts present twin research as neutral, objective and void of any kind of political connotations. We show how important leaders of German twin research have been historically managed, and how their contributions have been distorted and omitted. Reasons for historical revisionism by omission and for selectively revised accounts of the past are discussed. Suggestions for writing accounts of the twin method are included and focus on the necessity of self-reflection, considerations regarding one's own ethical-political inclinations, and review of the existing historical literature. In analyzing these connections, we attempt to understand how science, politics and history interact.

Concordance rates for smoking among African-American twins.

OBJECTIVES: Despite greater negative environmental influences such as lower socioeconomic status, less parental education, more single-parent households and urban dwelling, African Americans are less likely to begin smoking than European Americans. The goal of the current investigation was to examine the proportion of genetic and environmental influences on smoking in a sample of adult African-American twins. DESIGN: Birth records from North Carolina Register of Deeds Offices were used to identify participants for the Carolina African-American Twin Study of Aging (CAATSA). Participants completed an in-person interview that included measures of health status, cognition and psychosocial measures. PARTICIPANTS: Data for the analysis come from 200 pairs of same-sex twins (97 identical pairs and 113 fraternal), with a mean age = 46.9 years (SD = 13.9) and 38% of the sample being men. RESULTS: Compared to previous research on smoking, our estimates are very similar with genetics, accounting for about 60% of the individual variance in current smoking. We did find that there was a significant amount of genetic variance in pack years but no shared environmental influences. CONCLUSION: Similarity in proportions of genetic influences lead to larger questions about the genes involved in smoking among African Americans working in the same manner as in Caucasians or other groups. Additionally, this same question holds for the environmental variance. It is perhaps most likely that while the proportions of environmental variance are similar between groups that the actual source of variance (e.g., poverty, urban rural context, socioeconomic status, attitudes of family and friends) may differ when comparing ethnic groups.

Beliefs and practices concerning twins, hermaphrodites, and albinos among the Bamana and Maninka of Mali.

The Bamana and Maninka of Mali greatly value twins, and have elaborated a range of cultural beliefs and practices to assure their survival. Rates of twinning among these two ethnic groups average from 15.2/1000 to 17.9/1000 births compared to 10.5/1000 births (without assisted reproduction) in the United States and Great Britain. Twins (flaniw) are regarded as extraordinary beings with unusual powers, and as a gift from the supreme deity. A small altar (sinzin) is maintained in the home of twins, and periodic sacrifices of chicken blood, kola nuts, millet paste and millet beer regularly made to assure their protection. Albinos (yéfeguéw) and true and pseudo-hermaphrodites (tyéténousotéw) are also considered twin beings. However, they are believed to be the result of aberrant parental social behavior. The Bamana and Maninka believe that all four groups (twins, albinos, hermaphrodites, and pseudo-harmaphrodites) are closely linked to Faro, an androgynous supernatural being who provides equilibrium in the world. Faro is the original albino and hermaphrodite who gave birth to the first pair of twins after self-impregnation. Whenever a twin dies, a small wooden statue is sculpted called a flanitokélé (twin that remains). This commemorative figure is kept close to the surviving twin, reflecting a belief in the inseparability of twins. Eventually, the surviving twin takes responsibility for the figure. When a surviving twin marries, another figure is often sculpted in the opposite sex from the deceased twin, and placed with the original sculpture. Such commemorative sculptures are not created upon the death of those who are albinos, hermaphrodites, or pseudo-hermaphrodites. In recent years, transformational belief patterns have evolved as increasing numbers of Bamana and Maninka embrace Islam. Traditional beliefs are often given Islamic myths of origin. However, even in this Islamic context, many practices that assure twin survival are maintained.

Childhood pregnancy (10-14 years old) and risk of stillbirth in singletons and twins.

OBJECTIVE: To clarify the association between childhood pregnancy and risk of stillbirth. STUDY DESIGN: We analyzed singleton and twin pregnancies that occurred in children (10-14 years old) in the United States from 1989 to 2000. We estimated the absolute and relative risks of stillbirth by using 15- to19-year-old and 20- to 24-year-old mothers as comparison groups. RESULTS: The analysis involved 17.8 million singletons and 337,904 individual twins. The rate of stillbirth was highest in pediatric mothers for both singletons (12.8/1000) and twins (56/1000) compared with adolescent (6.8/1000 in singletons and 29/1000 in twins) and mature (5.5/1000 in singletons and 20/1000 in twins) mothers. After adjusting for confounding characteristics, pediatric mothers continued to exhibit significantly elevated risk for stillbirth in both singletons (odds ratio, 1.57; 95%CI, 1.49-1.66) and twins (odds ratio, 1.97; 95%CI, 1.42-2.73). Preterm birth rather than small size for gestational age was revealed by means of sequential modeling to account for the excess risk of stillbirth observed in pediatric gravidas. CONCLUSION: Pregnancy in childhood is a risk factor for stillbirth; shortened gestation rather than reduction in fetal growth is the mediating pathway.

Efficacy of retrospective recall of attention-deficit hyperactivity disorder symptoms: A twin study.

Attention-deficit hyperactivity disorder (ADHD) is currently recognized as a neurobiological, genetically based disorder in both children and adults. In this article we examine whether, by using a sample of middle-aged male twin veterans, the phenotypic characterization, prevalence, heritability and the longitudinal course of the illness is comparable to results observed in samples of children and adolescents. We evaluated the utility of adult reports of lifetime ADHD symptoms by examining the heritability of retrospectively reported childhood symptoms, using both symptom-based and discrete classification-based approaches, as well as examining the persistence of ADHD symptoms into adulthood for that subsample of individuals who were judged to possibly have ADHD as children. Our results showed prevalence rates that were approximately similar to those observed in other studies, demonstrable familiality, similar item endorsement patterns, a strong genetic association between hyperactive and inattentive subtypes, and a longitudinal decline in symptom severity. We concluded that while assessing ADHD in adult probands may be less accurate than with children or adolescents, since it demonstrates several characteristics in common with other assessment techniques it remains a viable diagnostic and research strategy, even with population samples.

Stillbirth and infant mortality among Hispanic singletons, twins, and triplets in the United States.

OBJECTIVE: We estimate the impact of increasing fetal number on fetal and infant mortality among Hispanic mothers. METHODS: Retrospective cohort study involving singletons, twins, and triplets delivered in the United States from 1995 through 2000, except for the analysis on infant mortality in singletons (1995 through 1999). Main outcome measures were stillbirth (> or = 20 weeks) and infant mortality (< 365 days). RESULTS: A total of 37,489,600 individual births were reviewed, consisting of 36,840,704 singletons, 613,930 twins, and 34,966 triplets. Hispanics accounted for 6,848,027 (18.6%) singletons, 85,887 (14.0%) individual twins, and 2,725 (7.8%) individual triplets. Among singletons, stillbirth (odds ratio [OR] 0.91, 95% confidence interval [CI] 0.90-0.92) and infant mortality (OR 0.85, 95% CI 0.84-0.86) were both lower in Hispanics than in whites. Among twins, Hispanics had a lower risk for infant mortality (OR 0.93, 95% CI 0.88-0.97) but a comparable risk for stillbirth (OR 1.06, 95% CI 0.98-1.13). Although the risk for infant mortality in Hispanic triplets was comparable to that of whites (OR 1.20, 95% CI 0.94-1.54), Hispanic triplets had a 50% higher likelihood of dying in utero (OR 1.50, 95% CI 1.06-2.14). CONCLUSION: Although Hispanic infants generally show better or comparable survival indices compared with whites, the risk for fetal and infant death in Hispanics increases in fetal number in a dose-dependent fashion, thereby obliterating the Hispanic advantage. The elevated risk for stillbirth among Hispanic triplets is particularly noteworthy and underscores the need for caution in making generalizations of favorable birth outcomes in Hispanics.

Understanding the covariation among childhood externalizing symptoms: genetic and environmental influences on conduct disorder, attention deficit hyperactivity disorder, and oppositional defiant disorder symptoms.

Conduct disorder (CD), attention deficit hyperactivity disorder (ADHD), and oppositional defiant disorder (ODD) are common childhood externalizing disorders that frequently co-occur. However, the causes of their comorbidity are not well understood. To address that question, we analyzed data from >600 Finnish twin pairs, who completed standardized interviews at age 14. Behavior genetic methods were used to examine how genetic/environmental factors contribute to each disorder's symptoms and to their covariation. We found significant genetic effects on each disorder with only modest evidence of shared environmental influences. Our data suggest the comorbidity among CD, ADHD, and ODD is primarily explained by shared genetic influences; however, each disorder was also under unique genetic influence, supporting the distinction of each disorder.

Mania in the Swedish Twin Registry: criterion validity and prevalence.

BACKGROUND: In population surveys, the assessment of mania is commonly done by trained lay interviewers using structured diagnostic instruments: the validity of this approach has been questioned. We examined the criterion validity and prevalence of lifetime mania in a survey of Swedish twins conducted with interview methodology usually applied in psychiatric epidemiology. METHODS: 41 838 individuals in the Swedish Twin Registry were evaluated via a telephone interview that included the eight DSM-IV mania items, and these data were merged with inpatient hospitalization discharge diagnoses from two comprehensive national registries (the criterion). An algorithm with eight cut-points was used to diagnose lifetime mania, and compared by a receiver operator characteristic curve to the criterion. The algorithm requiring at least four positive items resembling a DSM-IV diagnosis. RESULTS: History of hospitalization for a psychiatric condition that included a manic episode was present for 0.7% of all living twins, and predicted non-response to the survey (OR = 0.5; 95% CI = 0.4-0.6). The incidence rate for first hospitalization was 2.1/10 000 year(-1). For > or =1 symptom (first cut-point), the prevalence, sensitivity and specificity were 3.6%, 39.0% and 96.6%; for > or = 4 symptoms (DSM-IV-like cut-point) 2.6%, 36.5% and 97.6%; and for eight symptoms 0.3%, 18.0% and 99.8%. Positive predictive values were, respectively, 5.5%, 7.0% and 29.8%. CONCLUSIONS: The performance of the telephone screening for mania by lay interviewers in terms of positive predictive power was not satisfactory; despite a high specificity, the false positive rate was high. The low population prevalence of mania, non-response bias, criterion choice and inherent limitations of the interviewing method are among the explanations. Assessment of a lifetime manic episode based on lay interviewer screening may yield misleading data.

The effect of parental race on fetal and infant mortality in twin gestations.

Previous work has found that singleton birth outcomes are better if the father is black and the mother is white than if the father is white and the mother is black. We sought to examine the effects of parental race on fetal and infant mortality in twins. We analyzed the fetal and infant mortality rates in four groups [both parents white (W-W), both parents black (B-B), father black and mother white (FB-MW), and father white and mother black (FW-MB)], using the 1995--1997 U.S. twin registry data (249,221 twins). Compared to W-W, the infant mortality for B-B, FW-MB, and FB-MW (respectively, relative risk [RR] 1.84, 95% confidence interval [CI] 1.73-1.95; RR 1.39, 95% CI 1.03-1.51; and RR 1.49, 95% CI 1.26-1.77) were all significantly different from W-W but not from each other. When fetal mortality was added to infant mortality, the combined mortality was highest for B-B (RR 1.66, 95% CI 1.58-1.75), intermediate for FW-MB (RR 1.18, 95% CI 0.92-1.51) and FB-MW (RR 1.37, 95% CI 1.19-1.58) and lowest for W-W. Thus, twin infants born to black parents have higher risk of fetal and infant mortality compared with twin infants born to white parents and infants of mixed race parents generally have intermediate outcomes.

Parental race, birth weight, gestational age, and fetal growth among twin infants in the United States.

BACKGROUND: No previous study has examined the association between paternal race and birth weight among twins. AIMS: To examine the association of parents' race and birth weight among twins. STUDY DESIGN: Population-based retrospective cohort study to examine the association between parents' race and birth weight, and its two components, gestation duration and fetal growth among four group of infants: both parents blacks (FB-MB), father white and mother black (FW-MB), father black and mother white (FB-MW), and both parents whites (FW-MW), with "risk-free" analysis to control confounding factors. SUBJECTS: Twin births (304,466 twins) registered in the United States in 1995-1997. OUTCOME MEASURES: The means of birth weight, gestational age, and birth-weight-for-gestational age z score, and rates of very low birth weight (VLBW, <1500 g), very preterm birth (VPTB, <32 weeks of gestation), and fetal growth restriction (FGR, <10th percentile of z score). RESULTS: Means of birth weight, gestational age, and z score were 2234.0, 2301.9, 2361.1, and 2433.8, and 35.02, 35.24, 35.65, and 35.78, and -0.136, -0.070, -0.039, and 0.063, respectively, and the rates of VLBW, VPTB, and FGR were 14.5, 12.3, 10.5, and 8.1, and 16.0, 13.0, 11.6, and 9.2, and 12.6, 11.1, 10.8, and 8.7, respectively, in the FB-MB, FW-MB, FB-MW, and FW-MW groups. Excluding subjects with various risk factors by risk-free analysis did not change the results. CONCLUSIONS: Both parents' races are important determinants of birth weight, gestational age, and fetal growth among twin pregnancies, with higher effect on gestational age and greater maternal influence than paternal influence.