Developmental and Etiological Patterns of Substance Use from Adolescence to Middle Age: A Longitudinal Twin Study

Background: Common liability to addiction framework suggests the tendency to use substances is largely a general heritable liability, but little is known about how expression of this liability varies from adolescence to middle age. We evaluated average trajectories of development and covariation underlying commonly used substances using a genetically informative prospective design spanning three decades. Methods: Using a sample of 3,762 twins across 7 prospective waves of assessment spanning ages 14-40, we modeled these relationships using two complementary approaches: common factor modeling and piecewise latent growth modeling with measures of alcohol, tobacco, and marijuana useResults: We found phenotypic (rp ~.3-.9) and genetic covariation (rg ~.3-1) between a single common factor at each age, though the factor explained less shared variance over time. Average substance use increased across adolescence for all phenotypes and either declined in adulthood or remained stable; these trajectories were heritable (~.35-.75) across all stages of development. We also found shared environmental covariation underlying growth model intercepts reflecting use at age 16 (rc ~.7-1). Conclusions: A heritable common factor accounted for co-occurring substance use from mid-adolescence to mid-adulthood, and greater substance specificity emerged with maturation. Similarly, all stages of substance use development were heritable, but correlations between substances weakened across development. These results extend and reinforce prior work examining consumption and problem use, providing new evidence over a broad age range showing that individuals use substances more indiscriminately at younger ages and show preferences later.

The Babytwins Study Sweden (BATSS): A Multi-Method Infant Twin Study of Genetic and Environmental Factors Influencing Infant Brain and Behavioral Development

Twin studies can help us understand the relative contributions of genes and environment to phenotypic trait variation, including attentional and brain activation measures. In terms of applying methodologies such as electroencephalography (EEG) and eye tracking, which are key methods in developmental neuroscience, infant twin studies are almost nonexistent. Here, we describe the Babytwins Study Sweden (BATSS), a multi-method longitudinal twin study of 177 MZ and 134 DZ twin pairs (i.e., 622 individual infants) covering the 5−36 month time period. The study includes EEG, eye tracking and genetics, together with more traditional measures based on in-person testing, direct observation and questionnaires. The results show that interest in participation in research among twin parents is high, despite the comprehensive protocol. DNA analysis from saliva samples was possible in virtually all participants, allowing for both zygosity confirmation and polygenic score analyses. Combining a longitudinal twin design with advanced technologies in developmental cognitive neuroscience and genomics, BATSS represents a new approach in infancy research, which we hope to have impact across multiple disciplines in the coming years.

Days out of role and somatic, anxious-depressive, hypo-manic, and psychotic-like symptom dimensions in a community sample of young adults

Improving our understanding of the causes of functional impairment in young people is a major global challenge. Here, we investigated the relationships between self-reported days out of role and the total quantity and different patterns of self-reported somatic, anxious-depressive, psychotic-like, and hypomanic symptoms in a community-based cohort of young adults. We examined self-ratings of 23 symptoms ranging across the four dimensions and days out of role in >1900 young adult twins and non-twin siblings participating in the “19Up” wave of the Brisbane Longitudinal Twin Study. Adjusted prevalence ratios (APR) and 95% confidence intervals (95% CI) quantified associations between impairment and different symptom patterns. Three individual symptoms showed significant associations with days out of role, with the largest association for impaired concentration. When impairment was assessed according to each symptom dimension, there was a clear stepwise relationship between the total number of somatic symptoms and the likelihood of impairment, while individuals reporting ≥4 anxious-depressive symptoms or five hypomanic symptoms had greater likelihood of reporting days out of role. Furthermore, there was a stepwise relationship between the total number of undifferentiated symptoms and the likelihood of reporting days out of role. There was some suggestion of differences in the magnitude and significance of associations when the cohort was stratified according to sex, but not for age or twin status. Our findings reinforce the development of early intervention mental health frameworks and, if confirmed, support the need to consider interventions for subthreshold and/or undifferentiated syndromes for reducing disability among young people.

Unravelling the contribution of complex trauma to psychopathology and cognitive deficits: a cohort study

Background Complex traumas are traumatic experiences that involve multiple interpersonal threats during childhood or adolescence, such as repeated abuse. These traumas are hypothesised to cause more severe psychopathology and poorer cognitive function than other non-complex traumas. However, empirical testing has been limited to clinical/convenience samples and cross-sectional designs. Aims To investigate psychopathology and cognitive function in young people exposed to complex, non-complex or no trauma, from a population-representative longitudinal cohort, and to consider the role of pre-existing vulnerabilities. Method Participants were from the Environmental Risk Longitudinal Twin Study, a population-representative birth cohort of 2232 British children. At age 18 years (93% participation), we assessed lifetime exposure to complex and non-complex trauma, past-year psychopathology and current cognitive function. We also prospectively assessed early childhood vulnerabilities: internalising and externalising symptoms at 5 years of age, IQ at 5 years of age, family history of mental illness, family socioeconomic status and sex. Results Participants exposed to complex trauma had more severe psychopathology and poorer cognitive function at 18 years of age, compared with both trauma-unexposed participants and those exposed to non-complex trauma. Early childhood vulnerabilities predicted risk of later complex trauma exposure, and largely explained associations of complex trauma with cognitive deficits, but not with psychopathology. Conclusions By conflating complex and non-complex traumas, current research and clinical practice underestimate the severity of psychopathology, cognitive deficits and pre-existing vulnerabilities linked with complex trauma. A better understanding of the mental health needs of people exposed to complex trauma could inform the development of new, more effective interventions.

Babytwins Study Sweden (BATSS): A multi-method infant twin study of genetic and environmental factors influencing infant brain and behavioral development

ABSTRACTTwin studies can help us understand the relative contributions of genes and environment to phenotypic trait variation including attentional and brain activation measures. In terms of applying methodologies like electroencephalography (EEG) and eye tracking, which are key methods in developmental neuroscience, infant twin studies are almost non-existent. Here we describe the Babytwins Study Sweden (BATSS), a multi-method longitudinal twin study of 177 MZ and 134 DZ twin pairs (i.e. 622 individual infants) covering the 5 - 36 month time period. The study includes EEG, eye tracking and genetics, together with more traditional measures based on in-person testing, direct observation and questionnaires. The results show that interest in participation in research among twin parents is high, despite the comprehensive protocol. DNA analysis from saliva samples was possible in virtually all participants, allowing for both zygosity confirmation and polygenic score analyses. Combining a longitudinal twin design with advanced technologies in developmental cognitive neuroscience and genomics, BATSS represents a new approach in infancy research, which we hope to have impact across multiple disciplines in the coming years.

Bullying behaviours and other conduct problems: longitudinal investigation of their independent associations with risk factors and later outcomes

Purpose Bullying behaviours and other conduct problems often co-occur. However, we do not yet know whether bullying behaviours are associated with early factors and later poor outcomes independently of conduct problems. While there are differing, specific interventions for bullying behaviours and for conduct problems, it is unclear if such specificity is justified given parallels between both behaviours. Methods We used prospective data from the Environmental Risk (E-Risk) Longitudinal Twin Study, a nationally representative sample of 2232 children. Mothers and teachers reported on children’s bullying behaviours and conduct problems at ages 7 and 10. We collected measures of risk factors, including temperament and family factors, when children were age 5. We assessed behavioural, emotional, educational and social problems when participants reached the ages of 12 and 18. Results Bullying behaviours and conduct problems co-occurred in childhood. Our findings indicated that bullying behaviours and other conduct problems were independently associated with the same risk factors. Furthermore, they were associated with the same poor outcomes at both ages 12 and 18. Despite this, bullying behaviours were uniquely associated with behavioural, emotional, educational and social problems at age 18. Conclusions Our findings suggest that anti-bullying programmes and interventions aimed at reducing conduct problems could benefit from greater integration. Furthermore, our study highlights the mental health problems children who bully may face in later years and the need to consider those in intervention plans.

Examining the association between childhood autistic traits and adolescent hypomania: a longitudinal twin study

Background There is evidence that autism spectrum disorders (ASDs) co-occur with bipolar disorder (BD) relatively frequently. Individuals with BD often report symptoms of mania and hypomania during adolescence, prior to the age of onset for BD. It is unknown whether these symptoms are associated with ASDs. We examined whether diagnoses of ASDs and autistic traits were associated with hypomania in a large, population-based Swedish twin sample. Methods Parental structured interviews assessed autistic traits, and were used to assign screening diagnoses of ASDs, when twins were aged 9 or 12 (N = 13 533 pairs). Parents then completed questionnaires assessing hypomania when the twins were aged 15 and 18 (N = 3852 pairs at age 15, and 3013 pairs at age 18). After investigating the phenotypic associations between these measures, we used the classical twin design to test whether genetic and environmental influences on autistic traits influence variation in adolescent hypomania. Results Autistic traits and ASD diagnoses in childhood were associated with elevated scores on the measures of adolescent hypomania. Twin analyses indicated that 6–9% of the variance in hypomania was explained by genetic influences that were shared with autistic traits in childhood. When repeating these analyses for specific autistic trait domains, we found a stronger association between social interaction difficulties and hypomania than for other autistic trait domains. Conclusions These results indicate a genetic link between autistic traits and hypomania in adolescence. This adds to the growing evidence base of genetic factors associated with ASDs showing links with psychiatric outcomes across childhood and into adulthood.

The differential relations between ADHD and reading achievement: A quantile regression and quantile genetic approach.

This paper extends the understanding of the relation between ADHD and reading disability, through examining how this relation differs depending on the quantile an individual falls in for each. Samples from three twin projects around the United States were used (Florida Twin Project, Colorado component of International Longitudinal Twin Study of Early Reading Development, & Western Reserve Reading and Math Projects). Phenotypic analysis using quantile regression showed relations between ADHD related behaviors and reading comprehension to be stronger in the lower quantiles of reading comprehension in two of three samples. A new method was developed extending this analysis into the bivariate genetic space. Results of this quantile genetic analysis revealed that overlapping common environmental influences accounted for a larger proportion of variance in the lower quantiles of these variables in two of three samples. Finally, in all three samples the phenotypic relation was strongest when shared environmental influences accounted for a larger proportion of the overall variance.

Externalizing the threat from within: A new direction for researching associations between suicide and psychotic experiences

A recent suicidal drive hypothesis posits that psychotic experiences (PEs) may serve to externalize internally generated and self-directed threat (i.e., self-injurious/suicidal behavior [SIB]) in order to optimize survival; however, it must first be demonstrated that such internal threat can both precede and inform PEs. The current study conducted the first known bidirectional analysis of SIB and PEs to test whether SIB could be considered as a plausible antecedent for PEs. Prospective data were utilized from the Environmental Risk (E-Risk) Longitudinal Twin Study, a nationally representative birth cohort of 2232 twins, that captured SIB (any self-harm or suicidal attempt) and PEs at ages 12 and 18 years. Cross-lagged panel models demonstrated that the association between SIB at age 12 and PEs at age 18 was as strong as the association between PEs at age 12 and SIB at age 18. Indeed, the best representation of the data was a model where these paths were constrained to be equal (OR = 2.48, 95% CI = 1.63–3.79). Clinical interview case notes for those who reported both SIB and PEs at age 18, revealed that PEs were explicitly characterized by SIB/threat/death-related content for 39% of cases. These findings justify further investigation of the suicidal drive hypothesis.