The heritability of the skin conductance orienting response: a longitudinal twin study

Slower Peak Pupillary Response to Emotional Faces in Parents of Autistic Individuals

Background

Atypical autonomic arousal has been consistently documented in autism spectrum disorder (ASD) and is thought to contribute to the social-communication phenotype of ASD. Some evidence suggests that clinically unaffected first-degree relatives of autistic individuals may also show subtle differences in indices of autonomic arousal, potentially implicating heritable pathophysiological mechanisms in ASD. This study examined pupillary responses in parents of autistic individuals to investigate evidence that atypical autonomic arousal might constitute a subclinical physiological marker of ASD heritability within families of autistic individuals.

Methods

Pupillary responses to emotional faces were measured in 47 ASD parents and 20 age-matched parent controls. Macro-level pupillary responses (e.g., mean, peak, latency to peak) and dynamic pupillary responses over the course of the stimulus presentation were compared between groups, and in relationship to subclinical ASD-related features in ASD parents. A small ASD group (n = 20) and controls (n = 17) were also included for exploratory analyses of parent–child correlations in pupillary response.

Results

Parents of autistic individuals differed in the time course of pupillary response, exhibiting a later primary peak response than controls. In ASD parents, slower peak response was associated with poorer pragmatic language and larger peak response was associated with poorer social cognition. Exploratory analyses revealed correlations between peak pupillary responses in ASD parents and mean and peak pupillary responses in their autistic children.

Conclusion

Differences in pupillary responses in clinically unaffected parents, together with significant correlations with ASD-related features and significant parent–child associations, suggest that pupillary responses to emotional faces may constitute an objective physiological marker of ASD genetic liability, with potential to inform the mechanistic underpinnings of ASD symptomatology.

The genetic and environmental origins of emotional and cognitive empathy: Review and meta-analyses of twin studies

Empathy is considered a cornerstone of human social experience, and as such has been widely investigated from psychological and neuroscientific approaches. To better understand the factors influencing individual differences in empathy, we reviewed and meta-analyzed the behavioral genetic literature of emotional empathy- sharing others' emotions (k=13), and cognitive empathy- understanding others' emotions (k = 15), as manifested in twin studies. Results showed that emotional empathy is more heritable, 48.3 % [41.3 %-50.6 %], than cognitive empathy, 26.9 % [18.1 %-35.8 %]. Moreover, cognitive empathy as examined by performance tests was affected by the environment shared by family members, 11.9 % [2.6 %-21.0 %], suggesting that emotional understanding is influenced, to some degree, by environmental factors that have similar effects on family members beyond their genetic relatedness. The effects of participants' age and the method used to asses empathy on the etiology of empathy were also examined. These findings have implications for understanding how individual differences in empathy are formed. After discussing these implications, we suggest theoretical and methodological future research directions that could potentially elucidate the relations between genes, brain, and empathy.

Sex differences in the relations between infant temperament and electrodermal responses in early childhood

The present study examines the relationship between sex, infant temperament, and childhood psychophysiological reactivity via electrodermal activity (EDA). Both temperament and EDA are known to be relatively stable traits across the lifespan reflecting individual reactivity and regulation linked to suboptimal behavioral development and risk for psychopathology. However, little is known about the role of sex in the relationship between temperament and EDA. As a part of a larger longitudinal study of behavioral development, 125 participants were followed from birth till 3 years-old to examine the relationship between temperament and psychophysiological reactivity in different gender groups. Measurements of temperament at 6 months-old, and EDA, via skin conductance response (SCR) rate to a series of six startling auditory stimuli at 3 years-old were collected. Median splits of SCR scores and three temperament dimensions (positive affect, negative affect, and regulation) were created to designate high/low groups. Results indicate sex moderated the relationships between temperament traits and SCR rates. Specifically, low positive affect was associated with an increased risk for high psychophysiological reactivity in boys (odds ratio = 3.8), whereas high regulation was associated with an increased risk for greater reactivity in girls (odds ratio = 4.2). While preliminary, these findings suggest the importance of sex in relation to psychophysiological and temperamental reactivity, risk factors for developmental psychopathology. As our participants age, follow-up research to investigate the stability of these associations will provide valuable insights for the potential of EDA as a psychophysiological marker for developmental psychopathology risk in young children.

The genetics of anxiety-related negative valence system traits

NIMH's Research Domain Criteria (RDoC) domain of negative valence systems (NVS) captures constructs of negative affect such as fear and distress traditionally subsumed under the various internalizing disorders. Through its aims to capture dimensional measures that cut across diagnostic categories and are linked to underlying neurobiological systems, a large number of phenotypic constructs have been proposed as potential research targets. Since "genes" represent a central "unit of analysis" in the RDoC matrix, it is important for studies going forward to apply what is known about the genetics of these phenotypes as well as fill in the gaps of existing knowledge. This article reviews the extant genetic epidemiological data (twin studies, heritability) and molecular genetic association findings for a broad range of putative NVS phenotypic measures. We find that scant genetic epidemiological data is available for experimentally derived measures such as attentional bias, peripheral physiology, or brain-based measures of threat response. The molecular genetic basis of NVS phenotypes is in its infancy, since most studies have focused on a small number of candidate genes selected for putative association to anxiety disorders (ADs). Thus, more research is required to provide a firm understanding of the genetic aspects of anxiety-related NVS constructs. © 2016 Wiley Periodicals, Inc.

Endophenotype best practices

This review examines the current state of electrophysiological endophenotype research and recommends best practices that are based on knowledge gleaned from the last decade of molecular genetic research with complex traits. Endophenotype research is being oversold for its potential to help discover psychopathology relevant genes using the types of small samples feasible for electrophysiological research. This is largely because the genetic architecture of endophenotypes appears to be very much like that of behavioral traits and disorders: they are complex, influenced by many variants (e.g., tens of thousands) within many genes, each contributing a very small effect. Out of over 40 electrophysiological endophenotypes covered by our review, only resting heart, a measure that has received scant advocacy as an endophenotype, emerges as an electrophysiological variable with verified associations with molecular genetic variants. To move the field forward, investigations designed to discover novel variants associated with endophenotypes will need extremely large samples best obtained by forming consortia and sharing data obtained from genome wide arrays. In addition, endophenotype research can benefit from successful molecular genetic studies of psychopathology by examining the degree to which these verified psychopathology-relevant variants are also associated with an endophenotype, and by using knowledge about the functional significance of these variants to generate new endophenotypes. Even without molecular genetic associations, endophenotypes still have value in studying the development of disorders in unaffected individuals at high genetic risk, constructing animal models, and gaining insight into neural mechanisms that are relevant to clinical disorder.

Modifiable Arousal in Attention-Deficit/Hyperactivity Disorder and Its Etiological Association With Fluctuating Reaction Times

Background

Cognitive theories of attention-deficit/hyperactivity disorder (ADHD) propose that high within-subject fluctuations of cognitive performance in ADHD, particularly reaction time (RT) variability (RTV), may reflect arousal dysregulation. However, direct evidence of arousal dysregulation and how it may account for fluctuating RTs in ADHD is limited. We used skin conductance (SC) as a measure of peripheral arousal and aimed to investigate its phenotypic and familial association with RTV in a large sample of ADHD and control sibling pairs.

Methods

Adolescents and young adults (N = 292), consisting of 73 participants with ADHD and their 75 siblings, and 72 controls and their 72 siblings, completed the baseline (slow, unrewarded) and fast-incentive conditions of a RT task, while SC was simultaneously recorded.

Results

A significant group-by-condition interaction emerged for SC level (SCL). Participants with ADHD had decreased SCL, compared with controls, in the baseline condition but not the fast-incentive condition. Baseline SCL was negatively associated with RTV, and multivariate model fitting demonstrated that the covariance of SCL with RTV, and of SCL with ADHD, was mostly explained by shared familial effects.

Conclusions

ADHD is associated with decreased, but modifiable, tonic peripheral arousal. A shared familial cause underlies the relationship between arousal and RTV and between arousal and ADHD. Given the malleability of SCL, if our findings are replicated, it warrants further exploration as a potential treatment target for ADHD.

Brief Report: A Pilot Study of Parent-Child Biobehavioral Synchrony in Autism Spectrum Disorder

The theory of biobehavioral synchrony proposes that the predictive power of parent-child attunement likely lies in the manner with which behaviors are aligned with relevant biological processes. Symptoms of autism spectrum disorder (ASD) may challenge the formation of behavioral and physiological synchrony, but maintenance of such parent-child attunement could prove beneficial. The present study is the first to examine parent-child physiological synchrony in ASD. Parent and child electrodermal activity (EDA) was measured continuously during naturalistic free play. Parent-child EDA synchrony (positive covariation) was positively correlated with observed parent-child emotional attunement. Hierarchical linear modeling revealed that child ASD symptoms moderated the association between parent EDA and child EDA, such that EDA synchrony was stronger for children with lower ASD symptom levels.

Heritability and molecular genetic basis of electrodermal activity: a genome-wide association study

The molecular genetic basis of electrodermal activity (EDA) was analyzed using 527,829 single nucleotide polymorphisms (SNPs) in a large population-representative sample of twins and parents (N = 4,424) in relation to various EDA indices. Biometric analyses suggested that approximately 50% or more of variance in all EDA indices was heritable. The combined effect of all SNPs together accounted for a significant amount of variance in each index, affirming their polygenic basis and heritability. However, none of the SNPs were genome-wide significant for any EDA index. Previously reported SNP associations with disorders such as substance dependence or schizophrenia, which have been linked to EDA abnormalities, were not significant; nor were associations between EDA and genes in specific neurotransmitter systems. These results suggest that EDA is influenced by multiple genes rather than by polymorphisms with large effects.

Do our "big data" in genetic analysis need to get bigger?

Individual papers in this special issue might seem disappointing in their lack of discovery of specific genes of potential relevance to mental disorders. Yet, collectively, they yield information that could not be gleaned otherwise. Combining genome-wide complex trait analysis and classic approaches to estimate heritability in the same sample, and supplementing genome-wide association studies of common variants with exome and sequencing analyses, provides an unprecedented opportunity to examine major issues encountered in genetic research of complex traits, in ways not easily done with a series of unrelated studies using different samples, measures, and analytical approaches. Extending molecular genetic approaches to fully multivariate analyses will be an important future direction. These will require bigger analyses of even bigger big data, but will be essential in efforts to redefine psychopathology in the Research Domain Criteria (RDoC) approach promoted in the NIMH strategic plan.

Genetic covariance between psychopathic traits and anticipatory skin conductance responses to threat: Evidence for a potential endophenotype

The genetic architecture of the association between psychopathic traits and reduced skin conductance responses (SCRs) is poorly understood. By using 752 twins aged 9-10 years, this study investigated the heritability of two SCR measures (anticipatory SCRs to impending aversive stimuli and unconditioned SCRs to the aversive stimuli themselves) in a countdown task. The study also investigated the genetic and environmental sources of the covariance between these SCR measures and two psychopathic personality traits: impulsive/disinhibited (reflecting impulsive-antisocial tendencies) and manipulative/deceitful (reflecting the affective-interpersonal features). For anticipatory SCRs, 27%, 14%, and 59% of the variation was due to genetic, shared environmental, and nonshared environmental effects, respectively, while the percentages for unconditioned SCRs were 44%, 2%, and 54%. The manipulative/deceitful (not impulsive/disinhibited) traits were negatively associated with both anticipatory SCRs (r = -.14, p < .05) and unconditioned SCRs (r = -.17, p < .05) in males only, with the former association significantly accounted for by genetic influences (r g = -.72). Reduced anticipatory SCRs represent a candidate endophenotype for the affective-interpersonal facets of psychopathic traits in males.

Childhood EEG frontal alpha power as a predictor of adolescent antisocial behavior: a twin heritability study

High EEG frontal alpha power (FAP) is thought to represent a state of low arousal in the brain, which has been related in past research to antisocial behavior (ASB). We investigated a longitudinal sample of 900 twins in two assessments in late childhood and mid-adolescence to verify whether relationships exist between FAP and both aggressive and nonaggressive ASB. ASB was measured by the Child Behavioral Checklist, and FAP was calculated using connectivity analysis methods that used principal components analysis to derive power of the most dominant frontal activation. Significant positive predictive relationships emerged in males between childhood FAP and adolescent aggressive ASB using multilevel mixed modeling. No concurrent relationships were found. Using bivariate biometric twin modeling analysis, the relationship between childhood FAP and adolescent aggressive ASB in males was found to be entirely due to genetic factors, which were correlated r=0.22.

Skin conductance fear conditioning impairments and aggression: a longitudinal study

Autonomic fear conditioning deficits have been linked to child aggression and adult criminal behavior. However, it is unknown if fear conditioning deficits are specific to certain subtypes of aggression, and longitudinal research is rare. In the current study, reactive and proactive aggression were assessed in a sample of males and females when aged 10, 12, 15, and 18 years old. Skin conductance fear conditioning data were collected when they were 18 years old. Individuals who were persistently high on proactive aggression measures had significantly poorer conditioned responses at 18 years old when compared to others. This association was not found for reactive aggression. Consistent with prior literature, findings suggest that persistent antisocial individuals have unique neurobiological characteristics and that poor autonomic fear conditioning is associated with the presence of increased instrumental aggressive behavior.

The Southern California Twin Register at the University of Southern California: III

The Southern California Twin Register at the University of Southern California (USC) was initiated in 1984 and continues to provide an important resource for studies investigating genetic and environmental influences on human behavior. This article provides an update on the current register and its potential for future twin studies using recruitment through school district databases and voter records. An overview is also provided for an ongoing longitudinal twin study investigating the development of externalizing psychopathology from childhood to young adulthood, the USC Study of Risk Factors for Antisocial Behavior. Characteristics of the twins and their families are presented, including recruitment and participation rates, as well as attrition analyses and a summary of key findings to date.

The genetic and environmental etiology of decision-making: a longitudinal twin study

The present study examined the genetic and environmental etiology of decision-making (Iowa Gambling Task; Bechara, Damásio, Damásio, & Anderson, 1994), in a sample of twins at ages 11-13, 14-15, and 16-18 years. The variance across five 20-trial blocks could be explained by a latent "decision-making'' factor within each of the three times of IGT administration. This latent factor was modestly influenced by genetic factors, explaining 35%, 20% and 46% of the variance within each of the three times of IGT administration. The remaining variance was explained by the non-shared environment (65%, 80% and 54%, respectively). Block-specific non-shared environmental influences were also observed. The stability of decision-making was modest across development. Youth showed a trend to choose less risky decks at later ages, suggesting some improvement in task performance across development. These findings contribute to our understanding of decision-making by highlighting the particular importance of each person's unique experiences on individual differences.

Examining electrodermal hyporeactivity as a marker of externalizing psychopathology: a twin study

Literature suggests that reduced electrodermal reactivity (EDR) is related to externalizing problems. However, the genetic and environmental etiology of this association is unknown. Using a standard habituation paradigm, we measured responses to 15 loud tones in four cohorts of adolescent twins (N = 2,129). We quantified EDR as the average size of elicited responses (amplitude) and by counting the number of skin conductance responses (frequency). Externalizing liability was indexed through a general factor underlying substance-related problems and antisocial behavior. Response frequency, but not mean amplitude, was inversely associated with externalizing liability in each twin cohort. Biometric modeling revealed that most of the overlap between response frequency and externalizing liability was due to genetic influences common to both phenotypes. It is argued that neurological mechanisms involved in habituation may shed light on the etiology of psychopathology.