Profiles of Reactivity to Bullying Victimization: Genetic and Family Environment Predictors

This dissertation identified profiles of internalizing (anxiety and depression) and externalizing (delinquency and violence against peers) reactivity to bullying victimization (Aim 1) and then examined the influence of bullying characteristics (type—i.e., direct, indirect, dual—and frequency) (Aim 2), family characteristics (parental warmth and family conflict) (Aim 3), and selected genetic polymorphisms (5-HTTLPR, BDNF, and MAOA) (Aim 4) on membership in these profiles. The sample for addressing Aims 1-3 was 1,196 bullying victims who participated in the Context/Linkages Study in three North Carolina counties in Fall 2003 when they were in grades 8-10. The sample for addressing Aim 4 was a subset (n=281) of bullying victims who provided a biospecimen for genotyping. Five profiles were identified using latent profile analysis (Aim 1): a non-reactive profile and four profiles that captured combinations of internalizing and externalizing. Associations between bullying type and frequency on membership in these reactivity profiles were identified in Aim 2 using multinomial logistic regression. Direct victimization (i.e., physical violence, name calling) increased odds of membership in the high internalizers, high externalizers profile compared to all other profiles. Indirect victimization (i.e., damage to social relationships) increased odds of membership in the high internalizing profiles compared to the lower internalizing profiles. Dual (i.e., direct and indirect) victimization increased odds of membership in the high internalizers, high externalizers profile compared to each other profile. More frequent victimization increased odds of membership in the two high internalizing reactivity profiles compared to the non-reactor profile. Aim 3 tested the stress-buffering effects of parental warmth and the exacerbating effects of family conflict using logistic regression. The effects of parental warmth were different for boys and girls, with girls disproportionately benefitting from parental warmth. Family conflict increased likelihood of membership in the high internalizing, high externalizing profile compared to all others. The buffering and exacerbating effects were the same regardless of the frequency of the victimization experienced. Binary logistic regression analysis used for Aim 4 revealed no association between reactivity profile membership and genotype for the three candidate genes. Implications for intervention include recognition of heterogeneity in response to bullying and inclusion of family members.Doctor of Philosoph

Resting Heart Rate Variability (HRV) in Adolescents and Young Adults from a Genetically-Informed Perspective

Reduced heart rate variability (HRV) is associated with cardiac morbidity, mortality, and negative psychopathology. Most research concerning genetic influences on HRV has focused on adult populations, with fewer studies investigating the developmental period of adolescence and emerging adulthood. The current study estimated the genetic and environmental contributions to resting HRV in a sample of twins using various HRV time domain metrics to assess autonomic function across two different time measurement intervals (2.5- and 10-min). Five metrics of resting HRV [mean interbeat interval (IBI), the standard deviation of normal IBIs (SDNN), root square mean of successive differences between IBIs (RMSSD), cardiac vagal index (CVI), and cardiac sympathetic index (CSI)] were assessed in 421 twin pairs aged 14-20 during a baseline electrocardiogram. This was done for four successive 2.5-min intervals as well as the overall 10-min interval. Heritability (h2) appeared consistent across intervals within each metric with the following estimates (collapsed across time intervals): mean IBI (h2 = 0.36-0.46), SDNN (h2 = 0.23-0.30), RMSSD (h2 = 0.36-0.39), CVI (h2 = 0.37-0.42), CSI (h2 = 0.33-0.46). Beyond additive genetic contributions, unique environment also was an important influence on HRV. Within each metric, a multivariate Cholesky decomposition further revealed evidence of genetic stability across the four successive 2.5-min intervals. The same models showed evidence for both genetic and environmental stability with some environmental attenuation and innovation. All measures of HRV were moderately heritable across time, with further analyses revealing consistent patterns of genetic and environmental influences over time. This study confirms that in an adolescent sample, the time interval used (2.5- vs. 10-min) to measure HRV time domain metrics does not affect the relative proportions of genetic and environmental influences

Examining explanations for the link between bullying perpetration and physical dating violence perpetration: Do they vary by bullying victimization?

This short-term longitudinal study examined whether the association between bullying perpetration and later physical dating violence perpetration and mediators of that association (via anger, depression, anxiety, and social status), varied depending on level of bullying victimization. Differences have been noted between those who bully but are not victims of bullying, and those who are both bullies and victims. These differences may influence dating violence risk and the explanations for why bullying leads to dating violence. Data were from dating adolescents in three rural counties who completed self-administered questionnaires in the fall semester of grades 8-10 and again in the spring semester. The sample (N = 2,414) was 44.08% male and 61.31% white. Bullying perpetration in the fall semester predicted physical dating violence perpetration in the spring semester when there was no bullying victimization, but not when there was any bullying victimization. Bullying perpetration was positively associated with anger at all levels of bullying victimization and with social status when there was no or low amounts of victimization; it was negatively associated with social status at high levels of victimization. Bullying victimization was positively associated with anger, depression, and anxiety at all levels of bullying perpetration. Anger mediated the association between bullying perpetration and dating violence, regardless of level of victimization; depression, anxiety, and social status did not mediate the association at any level of bullying victimization. The findings have implications for dating violence prevention efforts and for future research on the link between bullying and dating violence