Gregory Carey

Genetic and environmental architecture of human aggression

A meta-analysis was performed on data from 24 genetically informative studies by using various personality measures of aggression. There was a strong overall genetic effect that may account for up to 50% of the variance in aggression. This effect was not attributed to methodological inadequacies in the twin or adoption designs. Age differences were important. Self-report and parental ratings showed genes and the family environment to be important in youth; the influence of genes increased but that of family environment decreased at later ages. Observational ratings of laboratory behavior found no evidence for heritability and a very strong family environment effect. Given that almost all substantive conclusions about the genetics of personality have been drawn from self or parental reports, this last finding has obvious and important implications for both aggression research in particular and personality research.

Sibling imitation and contrast effects

A general linear model is developed to account for the effects of direct phenotypic imitation and contrast of sibs on one another. Specific predictions from an imitation/contrast model depend upon three assumptions. They are (1) the type of process (imitation or contrast); (2) the stage of the process at the time phenotypes are measured; and (3) sibling constellation variables such as the number, sex composition, and age distribution of a sibling pedigree. For some models, phenotypic variance becomes a polynomial function of the imitation/contrast parameters and the covariances between the genotypes and the environments of sibling pairs. Consequently, phenotypic variances of different types of siblings [e.g., monozygotic (MZ) twins versus dizygotic (DZ) twins versus foster sibs] provide information about imitation or contrast. Thus, standardization of measures prior to analysis may unwittingly hide the statistical information that could detect these effects. The types of data needed to analyze imitation and contrast effects and the potential power of resolving these components of variation are discussed.

Codistribution of a sensory gating deficit and schizophrenia in multi-affected families

Because the clinical diagnosis of schizophrenia has not generally been an adequate phenotypic marker to detect the genes that convey risk for schizophrenia, efforts have been directed toward the identification of more elementary neuronal dysfunctions in schizophrenic patients and their families. Psychophysiological studies of sensory gating and selective attention suggest that defects in these brain functions are present in schizophrenic patients and some of their relatives. This study examines one of these defects in sensory gating, failure to suppress the P50 evoked response to repeated auditory stimuli. Six pedigrees, chosen because of the presence of large sibships containing several cases of schizophrenia, were studied. A mathematical model was developed to assess the familial association of the P50 defect with schizophrenia. The model preserves the quantitative nature of the data and is suitable for use in a sample with small numbers of pedigrees comprising many individuals. It is thus suitable for the evaluation of putative phenotypes in families to be studied by linkage analysis with polymorphic genetic markers. The results suggest that the P50 defect is familially associated with schizophrenia.

Inference About Genetic Correlations

In polygenic systems genetic correlations and the factors and specific genetic variances from genetic correlation matrices are often interpreted in terms of sets of genes common or specific to variables. While these inferences may indeed be true, a genetic correlation is not always sufficient evidence for the inferences. In some cases two variables with all genes in common can have low genetic correlations, and systems with only a few genes in common can have high genetic correlations. The assumptions about genic effects in polygenic systems and their effects on a genetic correlation are explicated and discussed. It is suggested that a distinction be made betweenbiological pleiotropism andstatistical pleiotropism to promote more accurate communication about the genetic associations among traits.

Variation in brain-derived neurotrophic factor (BDNF) gene is associated with symptoms of depression

BACKGROUND Brain-derived neurotrophic factor (BDNF) is putatively involved in the pathophysiology of depression. This study examined associations between BDNF genotype at the Val66Met locus, depression symptoms, and serum BDNF levels. METHODS Twenty-eight subjects in the primary study (25 female, 3 male) completed diagnostic interviews, self-report questionnaires, and provided blood samples for serum BDNF quantification and buccal cell samples for genotyping. Data from a second sample of 189 subjects (94 female, 95 male) were also analyzed. RESULTS The Val/Val genotype was associated with higher scores on the Cognitive-Affective factor of the Beck Depression Inventory-II (BDI-II) in the primary sample. No evidence was found for association between genotype and serum BDNF in this sample. Consistent with the primary study, Val/Val genotype was associated with higher total BDI-II scores, Cognitive-Affective factor scores, and Somatic-Vegetative factor scores, in the second sample. Serum BDNF measures were not available for the second sample. LIMITATIONS The mechanism through which BDNF genotype translates into (putative) differences in depression symptoms is not known. CONCLUSIONS In contrast to case-control association studies, we demonstrate two changes in the operationalization of the phenotype. Additionally, we found an association between Val/Val genotype and higher levels of depression symptoms. This result is distinct from an association between BDNF genotype and diagnosis of depression, and it may help to clarify our understanding of genetic liability to depression, which will ultimately lead to more nuanced and effective treatment strategies.

Heritability of MMPI personality indicators of psychopathology in twins reared apart

This report presents Minnesota Multiphasic Personality Inventory (MMPI) findings from the Minnesota Study of Twins Reared Apart. Data from 65 unique pairs of monozygotic twins reared apart (MZA) and 54 unique pairs of dizygotic twins reared apart (DZA) were analyzed. As in other results from this sample, MZA twins evidenced substantial similarity, highlighting the influence of shared genes. Biometric modeling yielded estimates of heritability for the MMPIs standard validity and clinical scales and for the Wiggins content scales ranging from .26 to .62 (M = .44), echoing previous findings from the twin and adoption literature on personality. The pattern of MZA and DZA correlations suggested nonadditive genetic effects for 3 MMPI scales. Multivariate profile analyses also suggested genetic influence on both profile elevation and shape.

A twin study of non-alcohol substance abuse

Except for alcohol abuse, little is known about the familial aggregation for substance abuse. Here we report twin resemblance for non-alcohol substance use in the Washington University Twin Series, wherein probands were identified by consecutive admission to psychiatric facilities in the St. Louis area. A 5-point substance abuse scale was constructed with values anchored by never used drugs (1) to drug dependence (5). Year of birth was the most powerful predictor of drug use--younger twins scored far higher than older twins. Either heritability or common environment had to be included in the regression model to avoid a significant drop in explained variance, but which was more important could not be resolved. The correlation for identical twins exceeded that for fraternal twins, suggesting the possibility of a heritable factor.

Genetic and environmental determinants of musical ability in twins

Analyses of musical ability data from the Loehlin and Nichols National Merit Scholarship study are presented. Musical ability is indexed by four measures: interest in a profession in music, performance in school, performance outside of school, and receiving honors in music. These variables pose a challenge for behavior genetic analysis since they do not conform to the assumptions of traditional linear models. For example, there is a dependent relationship between the honors and the performance variables; one cannot obtain honors without performance. Several methods were employed to deal with these relationships, and the following conclusions appeared regardless of the method used. First, twin correlations were always high, ranging from 0.44 to 0.90 in monozygotic (MZ) twins and from 0.34 to 0.83 in dizygotic (DZ) twins. Second, although there was evidence for heritable variation, the effects of common environment were almost always larger than the effects of heredity. Third, marital assortment was not of sufficient magnitude to account for these common environment effects. In the young adults in this sample, musical ability is influenced more by shared family environment than by shared genes.

Identifying Children in the Colorado Adoption Project at Risk for Conduct Disorder

Clustering techniques were used to identify a subsample of young adopted and nonadopted children in the Colorado Adoption Project at risk for conduct disorder. Although data from both boys and girls were analyzed, a cluster of girls large enough for subsequent statistical analysis could not be identified; therefore, results are reported for boys only. Identifying measures were selected based on the DSM-III-R diagnostic criteria. Cluster analyses confirmed the existence of a small group of boys who appeared to be significantly at risk. Subsequent parental and teacher ratings of these children verified the stability over time of the classification. The poor conduct group was significantly associated with difficult temperament in infancy, with poor conduct on the part of parents when they were youths, and with high achievement orientation in the home environment.

Genetics and Personality Inventories: The Limits of Replication with Twin Data

The consistency of twin data with personality questionnaires is examined using all reported twin samples which have been administered the California Psychological Inventory. The scale correlations for the MZ twins are fairly consistent across different samples while the correlations for DZ twins fail to show as much consistency. Differences, moreover, between MZ and DZ correlations fail to replicate across samples. Sampling error and sampling bias are proposed as the major reasons for the inconsistency, and when these factors are taken into account the resulting heritabilities suggest that the CPI scales loading on the extraversion-introversion factor are the most heritable. The implications of sampling error and sampling bias for estimating genetic parameters from correlational twin data, for uncovering differential heritability of personality traits, and for designing future research are discussed.