Schizophrenia (SZ) is a severe, complex, and common mental disorder with high heritability (80%), an adult age of onset, and high discordance (∼50%) in monozygotic twins (MZ). Extensive studies on familial and non-familial cases have implicated a number of segregating mutations and de novo changes in SZ that may include changes to the mitochondrial genome. Yet, no single universally causal variant has been identified, highlighting its extensive genetic heterogeneity. This report specifically focuses on the assessment of changes in the mitochondrial genome in a unique set of monozygotic twins discordant (MZD) for SZ using blood. Genomic DNA from six pairs of MZD twins and two sets of parents (N = 16) was hybridized to the Affymetrix Human SNP Array 6.0 to assess mitochondrial DNA copy number (mtDNA-CN). Whole genome sequencing (WGS) and quantitative polymerase chain reaction (qPCR) was performed for a subset of MZD pairs and their parents and was also used to derive mtDNA-CN estimates. The WGS data were further analyzed to generate heteroplasmy (HP) estimates. Our results show that mtDNA-CN estimates for within-pair and mother-child differences were smaller than comparisons involving unrelated individuals, as expected. MZD twins showed discordance in mtDNA-CN estimates and displayed concordance in directionality of differences for mtDNA-CN across all technologies. Further, qPCR performed better than Affymetrix in estimating mtDNA-CN based on relatedness. No reliable differences in HP were detected between MZD twins. The within-MZD differences in mtDNA-CN observed represent postzygotic somatic changes that may contribute to discordance of MZ twins for diseases, including SZ.

The error-related negativity (ERN) is a negative deflection in the event-related potential occurring when individuals make mistakes, and is increased in children with internalizing psychopathology. We recently found that harsh parenting predicts a larger ERN in children, and recent work has suggested that variation in the brain-derived neurotrophic factor (BDNF) gene may moderate the impact of early life adversity. Parents and children completed measures of parenting when children were 3 years old (N = 201); 3 years later, the ERN was measured and diagnostic interviews as well as dimensional symptom measures were completed. We found that harsh parenting predicted an increased ERN only among children with a methionine allele of the BDNF genotype, and evidence of moderated mediation: the ERN mediated the relationship between parenting and internalizing diagnoses and dimensional symptoms only if children had a methionine allele. We tested this model with externalizing disorders, and found that harsh parenting predicted externalizing outcomes, but the ERN did not mediate this association. These findings suggest that harsh parenting predicts both externalizing and internalizing outcomes in children; however, this occurs through different pathways that uniquely implicate error-related brain activity in the development of internalizing disorders.

Persistently elevated behavioral inhibition (BI) in children is a marker of vulnerability to psychopathology. However, little research has considered the joint influences of caregiver and child factors that may moderate the continuity of BI in early childhood, particularly genetic variants that may serve as markers of biological plasticity, such as the serotonin transporter linked polymorphic region (5-HTTLPR). We explored this issue in 371 preschoolers and their caregivers, examining whether parent characteristics (i.e., overinvolvement or anxiety disorder) and child 5-HTTLPR influenced the continuity of BI between ages 3 and 5. Measures were observational ratings of child BI, observational and questionnaire measures of parenting, and parent interviews for anxiety disorder history, and children were genotyped for the 5-HTTLPR. Parent factors did not moderate the association between age 3 and age 5 BI; however, child BI at age 3 interacted with children's 5-HTTLPR variants to predict age 5 BI, such that children with at least one copy of the short allele exhibited less continuity of BI over time relative to children without this putative plasticity variant. Findings are consistent with previous work indicating the 5-HTTLPR short variant increases plasticity to contextual influences, thereby serving to decrease the continuity of BI in early childhood.

Risk for depression is expressed across multiple levels of analysis. For example, parental depression and cognitive vulnerability are known markers of depression risk, but no study has examined their interactive effects on children's cortisol reactivity, a likely mediator of early depression risk. We examined relations across these different levels of vulnerability using cross-sectional and longitudinal methods in two community samples of children. Children were assessed for cognitive vulnerability using self-reports (Study 1; n = 244) and tasks tapping memory and attentional bias (Study 2; n = 205), and their parents were assessed for depression history using structured clinical interviews. In both samples, children participated in standardized stress tasks and cortisol reactivity was assessed. Cross-sectionally and longitudinally, parental depression history and child cognitive vulnerability interacted to predict children's cortisol reactivity; associations between parent depression and elevated child cortisol activity were found when children also showed elevated depressotypic attributions as well as attentional and memory biases. Findings indicate that models of children's emerging depression risk may benefit from the examination of the interactive effects of multiple sources of vulnerability across levels of analysis.

We have evaluated copy number variants (CNVs) in six monozygotic twin pairs discordant for schizophrenia. The data from Affymetrix® Human SNP 6.0 arrays™ were analyzed using Affymetrix® Genotyping Console™, Partek® Genomics Suite™, PennCNV, and Golden Helix SVS™. This yielded both program-specific and overlapping results. Only CNVs called by Affymetrix Genotyping Console, Partek Genomics Suite, and PennCNV were used in further analysis. This analysis included an assessment of calls in each of the six twin pairs towards identification of unique CNVs in affected and unaffected co-twins. Real time polymerase chain reaction (PCR) experiments confirmed one CNV loss at 7q11.21 that was found in the affected patient but not in the unaffected twin. The results identified CNVs and genes that were previously implicated in mental abnormalities in four of the six twin pairs. It included PYY (twin pairs 1 and 5), EPHA3 (twin pair 3), KIAA1211L (twin pair 4), and GPR139 (twin pair 5). They represent likely candidate genes and CNVs for the discordance of four of the six monozygotic twin pairs for this heterogeneous neurodevelopmental disorder. An explanation for these differences is ontogenetic de novo events that differentiate in the monozygotic twins during development.

Preliminary work indicates that cognitive vulnerability to depression may be associated with variants of the serotonin transporter promoter polymorphism (5-HTTLPR) and the valine to methionine at position 66 (val66met) polymorphism of the brain-derived neurotrophic factor (BDNF) gene; however, existing reports come from small samples. The present study sought to replicate and extend this research in a sample of 375 community-dwelling children and their parents. Following a negative mood induction, children completed a self-referent encoding task tapping memory for positive and negative self-descriptive traits. Consistent with previous work, we found that children with at least one short variant of the 5-HTTLPR had enhanced memory for negative self-descriptive traits. The BDNF val66met polymorphism had no main effect but was moderated by maternal depression, such that children with a BDNF methionine allele had a heightened memory for negative self-descriptive traits when mothers had experienced depression during children's lifetimes; in contrast, children with a methionine allele had low recall of negative traits when mothers had no depression history. The findings provide further support for the notion that the 5-HTTLPR is associated with cognitive markers of depression vulnerability and that the BDNF methionine allele moderates children's sensitivity to contextual factors.

The dopamine active transporter 1 (DAT1) gene is implicated in psychopathology risk. Although the processes by which this gene exerts its effects on risk are poorly understood, a small body of research suggests that the DAT1 gene influences early emerging negative emotionality, a marker of children's psychopathology risk. As child negative emotionality evokes negative parenting practices, the DAT1 gene may also play a role in gene–environment correlations. To test this model, children (N = 365) were genotyped for the DAT1 gene and participated in standardized parent–child interaction tasks with their primary caregiver. The DAT1 gene 9-repeat variant was associated with child negative affect expressed toward the parent during parent–child interactions, and parents of children with a 9-repeat allele exhibited more hostility and lower guidance/engagement than parents of children without a 9-repeat allele. These gene–environment associations were partially mediated by child negative affect toward the parent. The findings implicate a specific polymorphism in eliciting negative parenting, suggesting that evocative associations play a role in elevating children's risk for emotional trajectories toward psychopathology risk.

The degree of heterozygosity as determined by electrophoretic analysis of three or four polymorphic loci correlates positively with survival in age groups of the American oyster (Crassostrea virginica) collected as spat from two different natural populations. The phenomenon is shown to operate in ages from 2 weeks (post-settlement) to 3 years and appears to be general in populations of marine molluscs. The most likely explanation for this result is that heterozygosity improves survival through its effect on growth (heterozygotes grow faster). The effects of individual loci on viability are independent of each other. A direct involvement of the enzyme polymorphisms is the most probable genetic interpretation of the data, but associative overdominance cannot be excluded.