Behavioral genetic approaches to psychophysiological data

Rationale and design of a randomized factorial clinical trial of pharmacogenetic and adherence optimization strategies to promote tobacco cessation among persons with HIV

BACKGROUND

Tobacco use is approximately three times more common in people living with HIV (PLWH) than the general population. Moreover, current behavioral and pharmacological smoking cessation interventions are less effective for PLWH, highlighting a need for novel ways to optimize tobacco cessation treatments in this group. Prior research indicates that personalized treatment based on the nicotine metabolite ratio (NMR), a biomarker of nicotine metabolism, and augmenting smoking cessation medication adherence may improve cessation treatment for PLWH.

METHODS

In this 2 × 2 factorial design trial, 488 smokers with HIV receive 12 weeks of smoking cessation medication along with randomization to 1) tailor the smoking cessation drug to their metabolism or not, and 2) provide additional counseling on smoking cessation medication adherence or not. Those randomized to the pharmacogenetic optimization arm receive varenicline or the nicotine patch based on their NMR (varenicline for fast metabolizers and the nicotine patch for slow metabolizers) and those in the control arm receive varenicline. Those randomized to the experimental adherence counseling arm receive Managed Problem Solving (MAPS) targeting their smoking cessation medication and those in the control arm receive standard counseling.

CONCLUSION

PLWH on suppressive antiretroviral therapy who smoke lose more life-years due to tobacco use than to their HIV infection, and have lower response rates to current evidence-based treatments for smoking cessation. Both the NMR tailoring and MAPS interventions have the potential to optimize treatments for tobacco use among this population. If effective, this trial may demonstrate ways to further improve long-term health outcomes for PLWH.

Analysis of genetic influences on the consistency and variability of the Big Five across different stressful situations

Several studies have demonstrated that individual differences in personality traits, known as the Big Five, have a genetic component. These personality traits are considered important predictors of everyday behaviour. In addition to personality traits there are also factors in the environment that govern behaviour. This dual influence on behaviour is statistically reflected in a P × S interaction. This study examines the genetic and environmental influences on the interactions between a person and his daily life environment for the Big Five. Fifty‐seven identical twin pairs and 43 fraternal twin pairs participated in this study. Trait related behaviour was measured in 30 different situations with the aid of an SR inventory. The heritability coefficients for the main effect of P were in the normal range, varying between 0.35 for Agreeableness and 0.53 for Conscientiousness. The heritability coefficients for the P × S interactions were moderately high, explaining between 26% and 69% of the total P × S variance. The consequences of these results for general and behavioural genetic research on the Big Five will be discussed. Copyright © 2001 John Wiley & Sons, Ltd.

Heritability of cardiac vagal control in 24-h heart rate variability recordings: influence of ceiling effects at low heart rates

This study estimated the heritability of 24-h heart rate variability (HRV) measures, while considering ceiling effects on HRV at low heart rates during the night. HRV was indexed by the standard deviation of all valid interbeat intervals (SDNN), the root mean square of differences between valid, successive interbeat intervals (RMSSD), and peak-valley respiratory sinus arrhythmia (pvRSA). Sleep and waking levels of cardiac vagal control were assessed in 1,003 twins and 285 of their non-twin siblings. Comparable heritability estimates were found for SDNN (46%-53%), RMSSD (49%-54%), and pvRSA (48%-57%) during the day and night. A nighttime ceiling effect was revealed in 10.7% of participants by a quadratic relationship between mean pvRSA and the interbeat interval. Excluding these participants did not change the heritability estimates. The genetic factors influencing ambulatory pvRSA, RMSSD, and SDNN largely overlap. These results suggest that gene-finding studies may pool the different cardiac vagal indices and that exclusion of participants with low heart rates is not required.

Heritability of blood pressure increases during mental stress

We studied the influence of mental stress on the contributions of genes and environment to individual variation in systolic (SBP) and diastolic (DBP) blood pressure by structural equation modelling in 320 adolescent male and female twins. Blood pressure data were collected during rest and during a reaction time and a mental arithmetic task. Univariate analyses of SBP and DBP showed familial aggregation for blood pressure. A genetic explanation for this resemblance was most likely, although during rest conditions a model that attributed familial resemblance to shared environmental factors, also fitted the data. There was no evidence for sex differences in heritabilities. Multivariate analyses showed significant heterogeneity between sexes for the intercorrelations of the blood pressure data measured under different rest and task conditions. Multivariate genetic analyses were therefore carried out separately in males and females. For SBP and DBP in females and for SBP in males an increase in heritabilities was seen for blood pressure measured during stress, as compared to rest measurements. The influence of shared environ-mental factors decreased during stress. For DBP in males no significant contributions of shared environment were found. The multivariate analyses indicated that the same genetic and environmental influences are expressed during rest and stress conditions.

Genetic and environmental influences on impulsivity: a meta-analysis of twin, family and adoption studies

A meta-analysis of twin, family and adoption studies was conducted to estimate the magnitude of genetic and environmental influences on impulsivity. The best fitting model for 41 key studies (58 independent samples from 14 month old infants to adults; N=27,147) included equal proportions of variance due to genetic (0.50) and non-shared environmental (0.50) influences, with genetic effects being both additive (0.38) and non-additive (0.12). Shared environmental effects were unimportant in explaining individual differences in impulsivity. Age, sex, and study design (twin vs. adoption) were all significant moderators of the magnitude of genetic and environmental influences on impulsivity. The relative contribution of genetic effects (broad sense heritability) and unique environmental effects were also found to be important throughout development from childhood to adulthood. Total genetic effects were found to be important for all ages, but appeared to be strongest in children. Analyses also demonstrated that genetic effects appeared to be stronger in males than in females. Method of assessment (laboratory tasks vs. questionnaires), however, was not a significant moderator of the genetic and environmental influences on impulsivity. These results provide a structured synthesis of existing behavior genetic studies on impulsivity by providing a clearer understanding of the relative genetic and environmental contributions in impulsive traits through various stages of development.

Heritability and "environmentability" of electroencephalogram in infants: the twin study

We estimated relative contribution of genetic and environmental factors to electroencephalogram (EEG) frequency and amplitude parameters in infants. EEG was registered in 49 pairs of monozygotic and 45 pairs of dizygotic twins aged 7-12 months during (1) visual attention and (2) darkness. The variability of occipital alpha frequency depended mainly on genetic, probably nonadditive factors. The mean heritability for the spectral amplitudes in the delta, theta, and alpha bands were 0.37, 0.13, and 0.22 during visual attention, and 0.22, 0.40, and 0.10 during darkness. The influence of shared environment was probable for many of the EEG parameters. It was greatest for the amplitude of the theta rhythm during visual attention. The theta amplitude depended on such a parameter of early social environmental enrichment as the number of caregivers in the family. The possible relationship between infant theta rhythm and developmental outcome is discussed. For many of the EEG parameters, heritability increased during the second half of the first year of life, thus supporting the hypothesis about amplification of genetic effects and decrease of common environmental influences with age.

Genetic analysis of autonomic reactivity to psychologically stressful situations

We present the results of a behavioural genetics study on response profiles of autonomic measures (heart rate, blood pressure, and galvanic skin level), under ecologically valid, stressful conditions. Where response profiles of different physiological variables are the object of study, and when daily life stressors are taken into account (Turner and Hewitt, Annals of Behavioral Medicine, 14 (1992) 12-20), autonomic responsiveness to psychological stressors is thought to be an inherited trait. The participants were 100 female twin pairs, 57 monozygotic and 43 dizygotic twin pairs. Participants watched eight films with a stressful social content while autonomic measures were continuously recorded. Results show that the heritability coefficients of response profiles of autonomic measures are almost twice as high as that of single variables. The results further show that genes exert their influence on physiological behaviour not only directly, but also indirectly, by influencing the idiosyncratic relation between a person and his environment.

Individual differences in P300 amplitude: a genetic study in adolescent twins

Using quantitative genetic research designs, we decomposed phenotypic variance in P300 parameters into genetic and environmental components. The twin method was used to carry out this decomposition. Event related potentials (ERPs) were measured during a visual oddball paradigm in a sample of 213 adolescent twin pairs. The presence of male and female same-sex and opposite-sex twins in the sample enabled us to study sex differences in the contributions of genetic and environmental effects to P300 parameters. For targets and nontargets, half of the variance in the P300 amplitude is attributable to factors shared by the family members. However, it remains unclear whether this resemblance is attributable to shared environmental or genetic influences. The same factors (genetic or shared environmental) were found to contribute to the individual differences in males and females. The contributions do, however, differ across gender. Multivariate genetic analyses investigated the covariance among various brain areas to determine whether the covariance between two or more leads is attributable to the same genetic and/or the same environmental factors. The covariance of the P300 amplitude measured at different locations was attributable both to unshared environmental and to shared factors. Again it was not possible to show that the shared factors where either genetic or shared environmental.

Genetic analysis of the resting electroencephalographic power spectrum in human twins

Most twin studies have provided evidence for genetic effects on the electroencephalogram (EEG). In two twin studies, monozygotic (MZ) cotwin covariance for EEG power was greater than expected for additive gene actions, as compared with dizygotic (DZ) cotwin covariance. These findings were attributed to complex gene interactions, termed emergenesis. In the present study of 53 MZ and 38 DZ twin pairs departures from the additive genetic model were tested on resting EEG power. Total spectral power and the quotient of (beta band power)/(total power) both fit gene interaction models significantly better than did additive genetic models. These findings support the previous findings of MZ covariance for EEG power as much greater than DZ covariance; these findings can be explained entirely by the additive effects of genes. This pattern of twin covariances could be due to gene interactions but also to greater MZ than DZ environmental covariance.

Genetic architecture of EEG power spectra in early life

We measured the electroencephalogram (EEG) in 209 5 year old monozygotic (MZ) and dizygotic (DZ) twin pairs to estimate the relative contribution of genetic and environmental factors to EEG power spectra in early life. Data from same-sex and from opposite-sex twin pairs were used to test for sex differences in genetic influences. Results showed high concordance for EEGs of MZ twins for absolute and relative power in delta, theta, alpha 1, alpha 2, beta 1 and beta 2 bands. A model with additive genetic and unique environmental influences explained individual differences in both absolute and relative power in almost all bands and all electrode positions. Heritability of EEG power spectra was high. For absolute power the highest heritabilities were observed in theta, alpha 1, alpha 2 and beta 1 power bands (mean heritability 81, 81, 78, and 73%, respectively). Somewhat lower heritabilities were found in delta and beta 2 bands (mean heritability 55 and 64%, respectively). For relative power heritabilities were 63, 76, 71, 72, 68, and 65 for delta, theta, alpha 1, alpha 2, beta 1, and beta 2, respectively. Virtually no sex differences in heritability were found. These findings indicate that the background EEG is one of the most heritable characteristics in early life.

Heritable features of the auditory oddball event-related potential: peaks, latencies, morphology and topography

Baseline auditory ERP data from a larger study of the genetic determinants of the response to alcohol were collected from 59 monozygotic (MZ) twin pairs and from 39 same-sex dizygotic (DZ) twin pairs who drank socially. Three methods for measuring genetic influence on the ERPs were applied. First, based on maximum-likelihood estimates, the heritability of conventional peak amplitude and latency of N1 and P3 components was computed for each of 16 lead locations using tests of the significance of heritability based on intraclass correlations. P3 amplitude provided the strongest results, distributed symmetrically over caudal leads, and implied gene dominance as the mode of genetic transmission for the P3 component. A substantial genetic influence on N1 latency suggested a mixture of additive and dominance effects in the left fronto-temporal regions. N1 amplitude measures trended towards significant heritability, but none was observed for P3 latency. The second method used the maximum of the cross-correlation function to compare wave form shape in a lead-by-lead analysis of data from cotwins. Genetic influence was apparent in both target and non-target ERP responses, with a fronto-central topography of significant results. The third method reduced all spatial and temporal ERP differences from a pair of twins to a single scalar number for each response. Distributions of this global measure revealed significant genetic influence on both non-target and target ERPs. A post hoc analysis of the effect of gender on the heritability of N1 or P3 peaks and latencies revealed no statistically significant observations in this sample of young adult twins.

Familial influences on heart rate, blood pressure, and self-report anxiety responses to stress: results from 100 twin pairs

Two hundred healthy adolescent to middle-aged individuals (12-44 years, M = 20 years) were tested in a standardized stress protocol. These individuals comprised 20 monozygotic female, 20 monozygotic male, 20 same-sex dizygotic female, 20 same-sex dizygotic male, and 20 opposite-sex dizygotic twin pairs. Familial influences on heart rate, blood pressure, and self-report anxiety responses to four different kinds of stressors (Visual-Verbal Test for Conceptual Thought, mental arithmetic, isometric handgrip, cold pressor) were assessed using biometrical genetic model fitting. Evidence of significant genetic effects on resting heart rate and blood pressure was obtained, providing heritability estimates of .65, .63, and .58 for resting heart rate and systolic and diastolic blood pressure, respectively. Cardiovascular reactivity to the Visual-Verbal Test, mental arithmetic, and the cold pressor test appeared to be primarily influenced by genetic and idiosyncratic (nonfamilial) environmental factors, whereas reactivity to handgrip was more related to effects of the family environment. The results of multivariate model fitting suggested that the genetic effects on reactivity were relatively independent of those affecting resting heart rate and blood pressure and that there was significant overlap of genetic influences on heart rate and blood pressure responses to the two active coping tasks.

Phenotypic correlations between oculomotor functioning and schizophrenia-related characteristics in relatives of schizophrenic probands

Abnormalities of visual pursuit tracking are frequent in the first-degree relatives of probands with schizophrenia. The relationship between oculomotor abnormalities and schizophrenia-related characteristics in those family members, however, has received little attention. Fifty-three first-degree relatives of 24 probands with schizophrenia were evaluated for the presence of schizophrenia-related characteristics using both interview (Schedule for Schizotypal Personalities) and questionnaire (Chapman scales). The family members also had their eye movements recorded during pursuit tracking tasks and scored for gain in both the frequency and time domains, and saccadic intrusions. Social-interpersonal schizophrenia-related features were significantly related to both time- and frequency-domain gain calculations. It appears that abnormalities in the smooth-pursuit oculomotor system may be associated with symptoms conjectured to be most closely related to a genetic diathesis for schizophrenia. These findings provide further evidence that oculomotor abnormalities may be related to risk for this disorder.

Alternative common factor models for multivariate biometric analyses

In prior research we have shown how linear structural equation models and computer programs (e.g., LISREL) may be simply and directly used to provide alternatives for the traditional biometric twin design. We use structural equations and path models to define biometric group differences, we write traditional common-factor models in the same way, and then we take a detailed look at some alternative multivariate and biometric models. We contrast the biometric-factors covariance structure approach used by Loehlin and Vandenberg (1968), Martin and Eaves (1977), and others with the psychometric-factors approach used by McArdle et al. (1980) and others. We use the multivariate primary mental abilities data on monozygotic (MZ) and dizygotic (DZ) twins from Loehlin and Vandenberg (1968) to detail fundamental differences in model specification and results. We extend both multivariate biometric approaches using exploratory and confirmatory multiple-factor models. These comparisons show that each alternative multivariate methodology has useful features for empirical applications.

Resemblances of parents and twins in sports participation and heart rate

A model to analyze resemblances of twins and parents using LISREL is outlined and applied to sports participation and heart-rate data. Sports participation and heart rate were measured in 44 monozygotic and 46 dizygotic adolescent twin pairs and in their parents. Genetic factors influence variation in both sports behavior and heart rate, while there is no evidence for transmission from parental environment to offspring environment. For sports participation the data support a model in which there is a high positive correlation between environments of spouses and between environments of female twins. This correlation is absent for male twins and negative for opposite sex twins. For heart rate, a positive correlation between environmental influences was observed for all twins; there is no evidence for assortative mating. The proposed model can also handle data sets where parents and twins have been measured on more than one variable. This is illustrated by an application to the observed association of sports participation and heart rate.

Alcohol effects on the percentage of beta waves in the electroencephalograms of twins

Electroencephalogram (EEG) recordings were made from 26 pairs of monozygotic (MZ) and 26 pairs of dizygotic (DZ) adult male twins, before and after alcohol ingestion. After a baseline EEG and a light breakfast, 1.2 ml/kg of ethanol was given orally over 15 min and the EEG repeated four times at hourly intervals. Alcohol caused a significant drop in the percentage of beta waves (14-30 cycles/sec) during the 1st hr. For the percentage of beta waves in 38 pairs of twins with complete data, MZ twin beta-wave intraclass correlations (RMZ) ranged between 0.85 and 0.91 before and after alcohol, but the DZ intraclass correlations (RDZ) started at 0.54 and fell to 0.05 at 2 hr after alcohol before recovering to baseline levels. These correlations resulted in heritability estimates [2(RMZ-RDZ)] of 0.68 at baseline and 1.73 at 2 hr. A heritability of 1.43 was found for the 1st hr drop in percentage of beta waves (RMZ = 0.78, RDZ = 0.06). These unrealistically high heritabilities, due to RDZ's approaching 0.0, suggest a failure of assumptions in the linear twin model that was used. Also, these findings are similar to, but more exaggerated than, findings in resting EEG's and visually evoked EEG potentials of twins and are compatible with the influence of gene interactions.