Twin imitation for antisocial behavior: implications for genetic and family environment research

Linking Y-chromosomal short tandem repeat loci to human male impulsive aggression

INTRODUCTION

Men are more susceptible to impulsive behavior than women. Epidemiological studies revealed that the impulsive aggressive behavior is affected by genetic factors, and the male-specific Y chromosome plays an important role in this behavior. In this study, we investigated the association between the impulsive aggressive behavior and Y-chromosomal short tandem repeats (Y-STRs) loci.

METHODS

The collected biologic samples from 271 offenders with impulsive aggressive behavior and 492 healthy individuals without impulsive aggressive behavior were amplified by PowerPlex^RY23 PCR System and the resultant products were separated by electrophoresis and further genotyped. Then, comparisons in allele and haplotype frequencies of the selected 22 Y-STRs were made in the two groups.

RESULTS

Our results showed that there were significant differences in allele frequencies at DYS448 and DYS456 between offenders and controls (p < .05). Univariate analysis further revealed significant frequency differences for alleles 18 and 22 at DYS448 (0.18 vs 0.27, compared to the controls, p = .003, OR=0.57,95% CI=0.39-0.82; 0.03 vs 0.01, compared to the controls, p = .003, OR=7.45, 95% CI=1.57-35.35, respectively) and for allele 17 at DYS456 (0.07 vs 0.14, compared to the controls, p = .006, OR=0.48, 95% CI =0.28-0.82) between two groups. Interestingly, the frequency of haploid haplotype 22-15 on the DYS448-DYS456 (DYS448-DYS456-22-15) was significantly higher in offenders than in controls (0.033 vs 0.004, compared to the control, p = .001, OR = 8.42, 95%CI =1.81-39.24). Moreover, there were no significant differences in allele frequencies of other Y-STRs loci between two groups. Furthermore, the unconditional logistic regression analysis confirmed that alleles 18 and 22 at DYS448 and allele 17 at DYS456 are associated with male impulsive aggression. However, the DYS448-DYS456-22-15 is less related to impulsive aggression.

CONCLUSION

Our results suggest a link between Y-chromosomal allele types and male impulsive aggression.

Progression in substance use initiation: A multilevel discordant monozygotic twin design

Considerable attention has been paid to the "gateway" pattern of drug use initiation in which individuals progress from tobacco and alcohol use to cannabis and other illicit drugs. The extent to which this sequence reflects a causal impact of licit substance use on illicit substance involvement remains unclear. Clarifying the mechanisms underlying substance use initiation may help inform our understanding of risk for psychopathology, as increasing research is demonstrating associations between initiation patterns and heavier involvement. This study examined patterns of substance use initiation using a discordant twin design. Participants were 3,476 monozygotic twins (37% male) from the Australian Twin Registry who reported on their ages of tobacco, alcohol, and cannabis initiation. Multilevel proportional hazard regression models were used to (a) estimate within-twin-pair and between-twin-pair contributions to associations between the ages of onset of different drugs; and (b) examine whether the magnitude of effects differed as a function of the order of substance use initiation. Finding significant effects within twin pairs would support the hypothesis that the age of initiation of a substance causally influences the age of initiation of a subsequent substance. Finding significant effects between twin pairs would support the operation of familial influences that explain variation in the ages of initiation of multiple drugs. Within-twin-pair effects for typical patterns were modest. When initiation was atypical, however, larger within-twin-pair effects were observed and causal influences were more strongly implicated. Results support the utility of examining the timing and ordering of substance use initiation within sophisticated, genetically informative designs.

Aggression can be contagious: Longitudinal associations between proactive aggression and reactive aggression among young twins

The present study examined sibling influence over reactive and proactive aggression in a sample of 452 same-sex twins (113 male dyads, 113 female dyads). Between and within siblings influence processes were examined as a function of relative levels of parental coercion and hostility to test the hypothesis that aggression contagion between twins occurs only among dyads who experience parental coerciveness. Teacher reports of reactive and proactive aggression were collected for each twin in kindergarten (M = 6.04 years; SD = 0.27) and in first grade (M = 7.08 years; SD = 0.27). Families were divided into relatively low, average, and relatively high parental coercion-hostility groups on the basis of maternal reports collected when the children were 5 years old. In families with relatively high levels of parental coercion-hostility, there was evidence of between-sibling influence, such that one twin's reactive aggression at age 6 predicted increases in the other twin's reactive aggression from ages 6 to 7, and one twin's proactive aggression at age 6 predicted increases in the other twin's proactive aggression from ages 6 to 7. There was also evidence of within-sibling influence such that a child's level of reactive aggression at age 6 predicted increases in the same child's proactive aggression at age 7, regardless of parental coercion-hostility. The findings provide new information about the etiology of reactive and proactive aggression and individual differences in their developmental interplay.

The role of harsh discipline in explaining sex differences in conduct disorder: a study of opposite-sex twin pairs

In the current study, two hypotheses about the role of harsh discipline (HD) in explaining the sex difference in the prevalence of conduct disorder (CD) were evaluated: that boys exhibit more CD than girls because (1) they are exposed to more HD and/or (2) there is a greater association between HD and CD in boys. These hypotheses were evaluated in a sample of male and female adult twins from different families (N = 3,502) as well as a sample of adult twin brothers and sisters (N = 655) in order to examine the extent to which sex differences remained after controlling for between-family differences. Retrospective reports of HD experienced between ages 6-13 and DSM-IV CD symptoms experienced before age 18 were obtained via structured psychiatric telephone interviews. Boys reported higher mean levels of HD and CD than girls, both between and within families, and the results of model-fitting analyses suggested that differences in the use of harsh disciplinary practices for sons versus daughters may partially explain the sex difference in the prevalence of CD. Between families, the relation between HD and CD was greater for girls than boys, but within families, there was no evidence of a sex difference in the relation between HD and CD. Inconsistent between-family and within-family results suggest that factors that differ between families are confounded with sex differences in the relation between HD and CD. A more stringent test of sex differences involves eliminating these between-family differences by studying boys and girls within the same family.

The heritability of aptitude and exceptional talent across different domains in adolescents and young adults

The origin of individual differences in aptitude, defined as a domain-specific skill within the normal ability range, and talent, defined as a domain specific skill of exceptional quality, is under debate. The nature of the variation in aptitudes and exceptional talents across different domains was investigated in a population based twin sample. Self-report data from 1,685 twin pairs (12–24 years) were analyzed for Music, Arts, Writing, Language, Chess, Mathematics, Sports, Memory, and Knowledge. The influence of shared environment was small for both aptitude and talent. Additive and non-additive genetic effects explained the major part of the substantial familial clustering in the aptitude measures with heritability estimates ranging between .32 and .71. Heritability estimates for talents were higher and ranged between .50 and .92. In general, the genetic architecture for aptitude and talent was similar in men and women. Genetic factors contribute to a large extent to variation in aptitude and talent across different domains of intellectual, creative, and sports abilities.

Genetic and environmental contributions to common psychopathologies of childhood and adolescence: a study of twins and their siblings

We report findings based on analyses of self-reports of six common adolescent psychopathologies (attention deficit/hyperactivity disorder, ADHD; conduct disorder, CD; oppositional defiant disorder, ODD; generalized anxiety disorder, GAD; separation anxiety disorder, SAD; and major depressive disorder, MDD) in a sample of 1,162 male and female adolescent (12-19 years) twin pairs and 426 siblings. Prevalence statistics for past year and lifetime reports confirm differences between genders for CD, GAD, SAD, and MDD, and a lack of differences between twins and their non-twin siblings. Biometrical modeling was conducted to ascertain the relative influences of genes, and shared and non-shared environments contributing to these disorders. A more robust estimate of these parameters was obtained by including non-twin siblings. Age-specific thresholds were integrated into the analyses to appropriately model the developmental patterns of behavior. We found evidence for both genetic and non-shared environmental influences for all disorders. Shared environmental influences also seem to be important for MDD and lifetime GAD.

Interpersonal relationships and sex differences in the development of conduct problems

This article investigates the role of interpersonal relationships in shaping sex differences in the manifestation, etiology, and developmental course of conduct problems and their treatment needs. The review examines whether: (1) Girls' conduct problems are more likely than boys' to manifest as a function of disrupted relationships with caretakers and peers; (2) For girls more than for boys, the outcomes of conduct problems in adolescence and adulthood, and related treatment needs, are more likely to be a consequence of the quality of interpersonal relationships with others, particularly opposite-sex peers and partners. Evidence reviewed suggests that boys and girls share many similarities in their expression of conduct problems, but that a relational perspective does unify important differences. There is fair evidence that girls with conduct problems are more likely to come to the attention of authorities because of chaotic, unstable family relationships, and to express antisocial behavior in the context of close relationships; there is stronger evidence that the course and outcomes of conduct problems in females versus males pertain to interpersonal relationship impairments. Those sex differences map onto specific differences in treatment needs. Further empirical testing of the proposed relational model is indicated.

Cladistic association analysis of Y chromosome effects on alcohol dependence and related personality traits

Association between Y chromosome haplotype variation and alcohol dependence and related personality traits was investigated in a large sample of psychiatrically diagnosed Finnish males. Haplotypes were constructed for 359 individuals using alleles at eight loci (seven microsatellite loci and a nucleotide substitution in the DYZ3 alphoid satellite locus). A cladogram linking the 102 observed haplotype configurations was constructed by using parsimony with a single-step mutation model. Then, a series of contingency tables nested according to the cladogram hierarchy were used to test for association between Y haplotype and alcohol dependence. Finally, using only alcohol-dependent subjects, we tested for association between Y haplotype and personality variables postulated to define subtypes of alcoholism-antisocial personality disorder, novelty seeking, harm avoidance, and reward dependence. Significant association with alcohol dependence was observed at three Y haplotype clades, with significance levels of P = 0.002, P = 0.020, and P = 0.010. Within alcohol-dependent subjects, no relationship was revealed between Y haplotype and antisocial personality disorder, novelty seeking, harm avoidance, or reward dependence. These results demonstrate, by using a fully objective association design, that differences among Y chromosomes contribute to variation in vulnerability to alcohol dependence. However, they do not demonstrate an association between Y haplotype and the personality variables thought to underlie the subtypes of alcoholism.

A study of problem behaviors in 10- to 15-year-old biologically related and unrelated international adoptees

Genetic and environmental influences on problem behaviors were studied in a sample of international adoptees. Parental ratings of childrens' problem behaviors were obtained with the Child Behavior Checklist (CBCL). The sample (mean age, 12.4 years) comprised a group of biological siblings (111 pairs), a group of nonbiological siblings (221 pairs), and a group of singletons (94). Nonshared environmental influences were most important for problem behaviors studied in this paper. Genetic influences were substantial for Externalizing behaviors but unimportant for Internalizing behaviors. For the CBCL total problem score, Attention Problems, and Externalizing behaviors, the results of the present study were in agreement with findings from twin studies. The lack of genetic influences on Internalizing behaviors contrasts with results from twin studies. For the total problem score, the Externalizing grouping, Delinquent Behavior, and Aggressive Behavior, variances for singletons were significantly smaller than for siblings. Model fit indices indicated that these differences in variances are better attributed to smaller effects of factors associated with sibship size than to active influences of siblings on each other. Significant sex differences were found for 8 of the 10 scales. The larger variances for boys on the Externalizing grouping and Aggressive Behavior could be explained by genetic influences.

Genetic perspectives on crime

This article examines the empirical evidence for a genetic influence in the etiology of antisocial behavior. This review relates the results of studies from 3 approaches to genetic investigation. The first, family studies, provides valuable information about the increased risk for deviance among the family members of affected individuals. Family studies provide few conclusions about genetic etiology, however, because members of families share environments as well as genes. A second approach, the study of twins, offers a somewhat better separation of genetic and environmental effects. The twin studies compare monozygotic (MZ) twins, who are genetically identical, to fraternal, same-sex, dizygotic (DZ) twins who have no more genes in common than other siblings (50%). The research design assumes that the effect of hereditary factors is demonstrated if the MZ twins have more similar outcomes (concordance for deviance) than DZ twins. The twins are reared together in almost all studies, and the environmental influences for MZ pairs may be more similar than for DZ pairs. A third approach, the adoption study, largely overcomes the possibility of confounding genetic and environmental factors which limit inferences from the results of twin studies. In this method, the deviant outcomes of adopted children (separated early in life from their biological parents) are compared with the outcomes of their adoptive parents and their biological parents. Similarity in outcome between adoptees and biological parents indicates a genetic effect.