Biomedical subjects
Publications and source records attributed to R Plomin.
Quantitative genetic research on emotionality in animals and humans consistently points to genetic influence. Molecular genetic research is beginning to identify quantitative trait loci that are associated with the genetically related emotional domains of neuroticism, anxiety and depression.
The developmental interplay between nature and nurture is discussed, with particular reference to implications for research in developmental psychopathology. The general principles include individual differences in reactivity to the environment, two-way interplay between intraindividual biology and environmental influences, and the need to consider broader social contextual features. Individuals actively process their experiences; they also act on their environment to shape and select their experiences, and individual characteristics change over time. Key findings on genetic effects include their ubiquitous influence, the multifactorial origin of most psychopathology, the involvement of several genes in most mental disorders, some genetic effects operate through dimensional risk features rather than directly on disorder, some genetic effects are dependent on gene-environment correlations and interactions, and genetic effects increase with age. Key findings on environmental effects include their ubiquitous influence, the genetic mediation of some supposed environmental effects, the importance of passive gene-environment correlations, the paucity of evidence regarding environmental effects on lifetime liability to psychopathology, the lack of understanding of environmental effects on the organism, and the importance of nonshared environmental effects. Research strategies to investigate environmental risk mediation include the range of genetically sensitive designs, migration studies, secular trend investigations, studies of nonfamilial environments, and examination of intraindividual change in relation to measured environmental alterations. Proximal processes involved in person-environment interplay are discussed in relation to person-environment interactions and evocative and active person-environment correlations.
As specific genes are identified that are associated with behavior, it becomes increasingly important for behavioral geneticists to be able to incorporate these genes in their research. Rather than using blood, DNA can be extracted from cheek swabs, which makes it possible to obtain DNA inexpensively by mail from large, widely dispersed individuals. The purpose of this paper is to recommend this technique to the behavioral genetics community and to present results of our use of this technique to obtain DNA by mail for 114 2-year-olds and 116 adults.
Berman and Noble (1995) reported significantly reduced visuospatial performance in children with the TAQI A1 allele of the D2 dopamine receptor (DRD2) gene. Given that visuospatial performance loads highly on an unrotated principal component indexing general cognitive ability, we tested the association between DRD2 and WISC-R IQ comparing 51 high-IQ, 51 average-IQ, and 35 low-IQ children in the IQ Quantitative Trait Loci (QTL) Project. No statistically significant association between the TAQI A DRD2 alleles and IQ was found. Given that a statistically significant portion of genetic variance for specific cognitive abilities is independent of general cognitive ability, it is possible that the TAQI DRD2 association is specific to visuospatial performance and independent of general cognitive ability.
The genetic and environmental etiology of low general cognitive ability (g) during infancy and early childhood has not previously been investigated. The current study examined the genetic etiology of low cognitive ability at 14, 20, 24, and 36 months with twins from the MacArthur Longitudinal Twin Study. Low g groups were formed from the lowest 10th percentile at each age. Univariate probandwise concordance rates and DeFries-Fulker (J. C. DeFries & D. W. Fulker, 1985, 1988) multiple regression techniques suggest genetic etiology in low general cognitive ability groups. The stability of low general cognitive ability over time also appears to be primarily due to genetic factors. Although replication is necessary, these results suggest that the genetic etiology of low g during infancy and early childhood is at least as great as the heritability of g in the unselected population.
Previous research in the Swedish Adoption/Twin Study of Aging (SATSA) has found genetic influences on life events (R. Plomin, P. Lichtenstein, N.L. Pedersen, G.E. McClearn, & J.R. Nesselroade, 1990). The present study extends this finding by examining sex differences in genetic and environmental contributions to life events and by examining personality as a mediator of genetic influences on life events in SATSA. Analyses were based on 320 twin pairs, including identical and fraternal twins reared together and apart (mean age = 58.6 years). Controllable, desirable, and undesirable life events were revealed significant genetic variance for women. There was no significant genetic variance for either sex for uncontrollable events. Multivariate analyses of personality (as indexed by Neuroticism, Extraversion, and Openness to Experience) and life events suggest that all of the genetic variance on controllable, desirable, and undesirable life events for women is common to personality. Thus, in this sample of older adult women, genetic influences on life events appear to be entirely mediated by personality.
Although the adoption design is the most powerful method to disentangle nature and nurture, it has not been applied previously to developmental speech or language disorders. The present study examined the speech outcomes of 156 adopted and nonadopted children at varying risk for speech disorders based upon self-reported parental speech history. The sample consisted of four groups: (a) 16 adopted children with an affected biological parent; (b) 19 adopted children with an affected adoptive parent; (c) 31 nonadopted children with an affected natural parent; and (d) 90 low-risk adopted and nonadopted children with no parental speech disorder history. Results revealed that 25% of the children with a genetic background of speech disorder displayed questionable speech, language, or fluency skills at age 7, in comparison to 9% of the children with no known genetic history. Logistic regression analyses indicated that positive biological parental background was the best predictor of offspring affected status. The child's Full-Scale IQ and the HOME Scale of family environment were not significantly associated with speech outcome. These results provide additional evidence that genetic factors contribute importantly to the vertical transmission of some developmental speech disorders of unknown origin.
One of the fundamental questions for developmental psychopathology concerns the etiological links between the normal and abnormal. To what extent do disorders differ quantitatively or qualitatively from variation in the normal range? Genetic research on the normal and the abnormal differs in terms of concepts, methods, statistics, and target audiences. An approach, referred to as "DF" analysis, provides a framework for integrating these two worlds of genetic analysis. We applied traditional correlational analyses as well as DF (DeFries & Fulker, 1985) analyses to mother and father ratings of adjustment of adolescent siblings in a 3-year longitudinal twin and step-family study. At wave 1, the sample included 720 sibling pairs (average age of 12.9 years for the younger sibling and 14.5 years for the older siblings) and, in wave 2, 395 pairs still living at home. Both correlational analyses of the entire sample and DF analyses of selected extremes suggested moderate genetic influence and modest shared environmental influence for internalizing and externalizing behavior problems. Similar estimates were found for unselected individual differences and selected extreme groups. A framework is proposed that focuses on quantifying the etiologies of disorders (QED) as measured on continuous dimensions.
Twin studies are a powerful approach for estimating genetic and environmental influences in later life, but the usual requirement that both twins are alive may introduce a selection bias in gerontological studies relative to representative samples of nontwins. In the present study, samples of older twins and nontwins in Sweden were compared across the domains of vitality, well-being, physical and cognitive functioning, and health utilization to evaluate possible selection bias. One member of each twin dyad in the OCTO-Twin Study of intact twin pairs older than age 80 was randomly selected (N = 128) and compared with a population-based sample of nontwins (N = 324) from the OCTO Study. Multiple regressions adjusting for differences in demographic variables showed significant effects for twin status in only 3 of 20 comparisons. The results suggest that twin pairs surviving into very late life are similar to a representative sample of nontwins of the same age in health status and biobehavioral functioning. These findings support the generalizability of twin studies for understanding genetic and environmental influences on aging, health, and behavior.
BACKGROUND: The opportunities for psychiatry deriving from available or likely genetic advances are reviewed. METHOD: Clinical implications are considered in the context of both the misconceptions and benefits associated with relevant genetic findings. RESULTS: Misconceptions include that: heritability estimates have a 'true' fixed value; a high heritability means that environmental interventions will be ineffective; a high heritability within groups means that differences between groups will also be due to genes; genetic effects are determinative; 'genetic' means single abnormal genes; genes associated with disease must be bad and justify eugenic measures; gene therapy will be widely applicable; and genetic screening of the general population will be useful. The benefits include demonstrations that: both genes and environment have an ubiquitous influence; some prevailing diagnostic assumptions are mistaken; genes influence development; the effects of nature and nurture are not separate; and environmental effects tend to be person-specific. The potential value of molecular genetics lies in elucidation of causal processes as they apply to both brain systems and nature-nurture interplay; improving diagnosis and genetic counselling; and the development of improved pharmacological interventions. CONCLUSION: Advances in genetics will make a major impact on clinical psychiatry, and should bring practical benefits for both prevention and treatment.
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Genetics has substantial relevance to behavioral medicine. A rapidly growing body of evidence indicates the influence of genetics on health and disease and on the behavioral factors related to them. The model of quantitative genetics provides a general interpretational scheme for this burgeoning field. The model focuses on variability, and a major research objective is the decomposition of observed individual differences into portions attributable to various types of genetic and environmental sources of variability. This approach emphasizes the coaction of genes and environments and stands in sharp contrast to the archaic view that places nature and nurture in opposition. Some relevant examples are given in this first article to illustrate the general analytic process. A detailed application to cardiovascular health and disease is provided in the second article, and some policy implications are briefly considered in the third article.
OBJECTIVE: To briefly summarize behavioral genetic findings in relation to child and adolescent psychopathology, paying special attention to the environmental rather than genetic components of variation, and to describe recent research exploring specific nonshared environmental processes in the development of adolescent depression. METHOD: Behavioral genetic studies of child and adolescent psychopathology were outlined, with special attention given to findings from the Nonshared Environment and Adolescent Development Project. This project was also used to explore maternal negativity as a "candidate" nonshared environmental influence for adolescent depression. RESULTS: These studies indicate that the environmental factors influencing developmental psychopathology are primarily of the nonshared variety (with the notable exception of juvenile delinquency). In addition, consistent results have not yet emerged from assessments of adolescent depression. Finally, maternal negativity was identified as a specific nonshared environmental factor related to adolescent depression. CONCLUSIONS: The environment as well as genetics is important to understanding childhood psychiatric disorders, and behavioral genetic designs provide the best evidence for this. Specifically, environments not shared by siblings are particularly salient. From a clinical standpoint, these considerations point to the importance of assessing the entire family rather than only the family member with the "problem."
Behavioural genetic research has shown that environmental influences relevant to the development of individual differences are largely nonshared in origin. That is, environmental influences do not make children in the same family similar to one another, however, little is known about which specific aspects of the environment are responsible. Identical (MZ) twins provide a uniquely powerful tool to search for specific nonshared environmental influences independent of nonshared genetics because such twins do not differ genetically. The sample consisted of 93 MZ twin pairs aged 10-18 years from the Nonshared Environment and Adolescent Development (NEAD) project. Reports of parental negativity and adolescent adjustment were obtained from parents, ratings of videotaped observations, and the adolescents themselves. Relative differences of mothers' and fathers' negativity within MZ pairs correlated significantly with MZ differences in antisocial behaviour. The correlations were moderate for within-reporter associations, but were negligible for associations between reporters. Possible interpretations for these source-specific findings are discussed.
Parent ratings of temperament in infancy and childhood yield evidence for genetic influence in twin studies but not in adoption studies. The present study used the sibling adoption design to investigate teacher and tester ratings of temperament in middle childhood. When each child was 7 years old, ratings on the Colorado Childhood Temperament Inventory were obtained from a teacher and tester for more than 50 pairs each of adoptive and nonadoptive siblings in the Colorado Adoption Project. Significant genetic influence emerged for both teacher and tester ratings of Activity, for tester ratings of Sociability, and for teacher ratings of Emotionality. Results obtained from bivariate genetic analysis suggest that the modest covariance between teacher and tester ratings of Activity is entirely mediated genetically. Except for teacher ratings of Attention Span, evidence of shared family environment was nonsignificant, despite the power of the sibling adoption design to detect it.
BACKGROUND: Recent genetic evidence suggests that the most important environmental influences on normal and pathologic development are those that are not shared by siblings in the same family. We sought to determine the relationship between differences in parenting styles and depressive symptoms and antisocial behavior in adolescence, and to compare the influence of these nonshared experiences with genetic influences. METHODS: We studied 708 families with at least two same-sexed adolescent siblings who were monozygotic twins (93 families), dizygotic twins (99 families), ordinary siblings (95 families), full siblings in step families (181 families), half siblings in step families (110 families), and genetically unrelated siblings in step families (130 families). Data on parenting style were collected by questionnaire and by video recording of interaction between parents and children. RESULTS: Almost 60% of variance in adolescent antisocial behavior and 37% of variance in depressive symptoms could be accounted for by conflictual and negative parental behavior directed specifically at the adolescent. In contrast, when a parent directed harsh, aggressive, explosive, and inconsistent parenting toward the sibling, we found less psychopathologic outcome in the adolescent. CONCLUSIONS: Parenting behavior directed specifically at each child in the family is a major correlate of symptoms in adolescents. Furthermore, harsh parental behavior directed at a sibling may have protective effects for adolescents, a phenomenon we call the "siblin barricade."
To test the hypothesis that the etiology of covariation among measures of cognitive ability and academic achievement is due at least in part to shared genetic influences, data from 198 adoptive and 220 nonadoptive families participating in the Colorado Adoption Project were subjected to multivariate behavioral genetic analyses. Data on measures of cognitive ability (verbal comprehension and perceptual organization) and academic achievement (reading recognition and mathematics achievement) from related and unrelated sibling pairs tested at age 7, as well as from adoptive and nonadoptive parents, were analyzed. Phenotypic analyses confirmed previous findings of moderate correlations among measures of cognitive ability and achievement, averaging about .35. Although 54% of the covariation between reading and mathematics achievement was due to influences shared with verbal ability, a significant proportion of this covariation was independent of the cognitive ability measures. Heritabilities for the various measures were moderate, ranging from .21 to .37. Moreover, genetic influences accounted for 33-64% of their phenotypic covariation; for example, 33-60% of the observed correlations between verbal comprehension and the achievement measures, 64% of those between perceptual organization and the achievement measures, and 63% of that between reading recognition and mathematics achievement were due to shared genetic influences. Similar to the results of the phenotypic analysis, nearly half of the genetic covariance between reading and mathematics achievement was independent of cognitive ability. Their remaining covariance was due primarily to nonshared environmental influences.