The nature of nurture: Genetic influence on “environmental” measures

Cardiff depression study. A sib-pair study of life events and familiality in major depression

BACKGROUND

An excess of both depression and undesirable life events in first-degree relatives of probands with depression as compared with controls has been reported. This association may have reflected a familial factor in common.

AIMS

To examine the familiality of life events and depression and whether there may be a common familial factor influencing vulnerability to depression and the experiencing of life events.

METHOD

In a sib-pair design, 108 probands with depression and their siblings were compared with 105 healthy controls and their siblings for psychopathology and life events.

RESULTS

The lifetime relative risk of depressive disorder in the siblings of depressed subjects as compared with siblings of controls was 9.74, although these groups did not differ in the life events measures. Several categories of events showed significant sibling correlations, but this was due to the same event affecting both members of the pair.

CONCLUSIONS

Although depressive disorder was strongly familial, the familial effects on life events were largely explained by shared experiences. There was no evidence for a common factor influencing both depression and life events.

Nonshared environment: a theoretical, methodological, and quantitative review

When genetic similarity is controlled, siblings often appear no more alike than individuals selected at random from the population. Since R. Plomin and D. Daniels' seminal 1987 review, it has become widely accepted that the source of this dissimilarity is a variance component called nonshared environment. The authors review the conceptual foundations of nonshared environment, with emphasis on distinctions between components of environmental variance and causal properties of environmental events and between the effective and objective aspects of the environment. A statistical model of shared and nonshared environmental variables is developed. A quantitative review shows that measured nonshared environmental variables do not account for a substantial portion of the nonshared variability posited by biometric studies of behavior. Other explanations of the preponderance of nonshared environmental variability are suggested.

Psychosocial adversity and child psychopathology

BACKGROUND

Despite strong claims that 'genetic theory' should replace 'socialisation theory', there are good grounds for taking seriously the notion that there are psychosocial influences on child psychopathology.

AIMS

To re-evaluate this issue in the light of developments over the past half-century.

METHOD

A wide-ranging review of topics related to this issue, 1948-1998.

RESULTS AND CONCLUSIONS

The findings are used to consider the challenges still to be met as we enter the next century. It is argued that it is necessary to put aside the absurd brain-mind dualisms of the past.

Etiology of the impulsivity/aggression relationship: genes or environment?

Genetic and environmental influences on the phenotypic relationship between the Barratt Impulsiveness Scale and the aggression scales from the Buss-Durkee Hostility Inventory in adult males were examined. This study used 182 pairs of male MZ twins and 118 pairs of male DZ twins from the Vietnam Era Twin Registry. Phenotypic relationships between the measure of impulsivity and subscales of the measure of aggression (direct assault, verbal assault, indirect assault, and irritability) ranged from 0.22 to 0.51. Genetic and environmental mediation of the phenotypic relationship between impulsivity and aggression were approximately the same for all four models. Multivariate model-fitting analysis indicated that irritability and impulsivity had a larger phenotypic relationship, as well as a greater portion of shared genes and environment than the other three subscales of aggression. This suggests, for example, that there are more overlapping genetic and environmental influences accounting for the relationship between irritability and impulsivity than between direct assault and impulsivity. The effects of such findings on our understanding of impulsive aggression are discussed.

Neurobiology of attention-deficit hyperactivity disorder

Attention-deficit hyperactivity disorder (ADHD) is an early-onset, clinically heterogeneous disorder of inattention, hyperactivity, and impulsivity. Family, twin, adoption, segregation analysis, and molecular genetic studies show that is has a substantial genetic component. Although their results are still tentative, molecular genetic studies suggest that three genes may increase the susceptibility to ADHD: the D4 dopamine receptor gene, the dopamine transporter gene, and the D2 dopamine receptor gene. Studies of environmental adversity have implicated pregnancy and delivery complications, marital distress, family dysfunction, and low social class. The pattern of neuropsychological deficits found in ADHD children implicate executive functions and working memory; this pattern is similar to what has been found among adults with frontal lobe damage, which suggests that the frontal cortex or regions projecting to the frontal cortex are dysfunctional in at least some ADHD children. Moreover, neuroimaging studies implicate frontosubcortical pathways in ADHD. Notably, these pathways are rich in catecholamines, which have been implicated in ADHD by the mechanism of action of stimulants--the class of drugs that effectively treats many ADHD children. Yet human studies of the catecholamine hypothesis of ADHD have produced conflicting results, perhaps due to the insensitivity of peripheral measures.

Independence of childhood life events and chronic adversities: a comparison of two patient groups and controls

OBJECTIVE

To examine the differences between independent and behavior-dependent stressful life events and chronic adversities in child psychiatric patients, community controls, and children with asthma.

METHOD

The Psychosocial Assessment of Childhood Experiences was used to assess recent severe events (life events with high long-term threat) and major adversities (long-term experiences with high negative impact on child) in children attending a psychiatric clinic (n = 99), community controls (n = 26), and children with chronic asthma (n = 94).

RESULTS

In the previous year, the psychiatric patients had, on average, experienced significantly more independent and behavior-dependent severe events and major adversities than either the controls or the asthmatic patients. The differences were most pronounced in relation to behavior-dependent high-threat life events and long-term-experiences. Among the psychiatric patients, one third of all severe events and one quarter of all major adversities were dependent on the child's behavior. The corresponding proportions in the controls and children with asthma were between one fifth and one twelfth.

CONCLUSIONS

Psychiatrically disturbed children have an increased risk of experiencing behavior-dependent life events and long-term adversities compared with their peers in the community at large and compared with children suffering from a chronic physical illness such as asthma. Future studies need to examine the possible contributions of such experiences to the development and maintenance of psychiatric and physical illness in children.

Does childhood trauma cause personality disorders in adults?

OBJECTIVE

To examine the relationship between trauma in childhood and personality disorders in adulthood.

METHOD

A review of the literature was conducted.

RESULTS

The reported associations between trauma and personality pathology are illuminated by the following research findings: 1) personality is heritable; 2) only a minority of patients with severe personality disorders report childhood trauma; and 3) children are generally resilient, and traumatic experiences do not consistently lead to psychopathology.

CONCLUSIONS

The role of trauma in the personality disorders is best understood in the context of gene-environment interactions.

On models and muddles of heritability

One reason for the astonishing persistence of the IQ myth in the face of overwhelming prior and posterior odds against it may be the unbroken chain of excessive heritability claims for 'intelligence', which IQ tests are supposed to 'measure'. However, if, as some critics insist, 'intelligence' is undefined, and Spearman's g is beset with numerous problems, not the least of which is universal rejection of Spearman's model by the data, then how can the heritability of 'intelligence' exceed that of milk production of cows and egg production of hens? The thesis of the present review paper is that the answer to this riddle has two parts: (a) the technical basis of heritability claims for human behavior is just as shaky as that of Spearman's g. For example, a once widely used 'heritability estimate' turns out to be mathematically invalid, while another such estimate, though mathematically valid, never fits any data; and (b) valid technical criticisms of flawed heritability claims typically are met with stubborn editorial resistance in the main stream journals, which tends to calcify such misinformation.

Evolutionary psychology and genetic variation: non-adaptive, fitness-related and adaptive

Behavioural variation across individuals can be substantial. A broad generalization emerging from three decades of behavioural genetic studies is that most psychological individual differences have moderate broad heritabilities (30-60%). There are at least three possible scenarios for this genetic variation. First, it may be adaptively neutral and not subject to selection. Second, it may be related to fitness despite selection. Third, it may be maintained by selection for alternative adaptations. Some authors favour the first of these possibilities, but the latter two cannot be ruled out. First, temporally varying selection pressures (e.g. pathogens) can maintain fitness-related genetic variance in a population despite current selection pressures. Moreover, direct and indirect evidence on humans support the notion that some phenotypic variance is fitness related. Second, while adaptive alternatives are unlikely to be found at a level of highly complex design, frequency dependent selection can maintain variation at finer, quantitative levels. One potential example is discussed. Because of their particular relevance to evolutionary psychology, fitness-related and adaptive genetic variance deserve further attention.

Opportunities for psychiatry from genetic findings

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.

Implications of genetic research for child psychiatry

OBJECTIVE

To review implications of genetic research in child psychiatry.

METHOD

Key advances in quantitative and molecular genetics are noted and findings are summarized with respect to autism, attention-deficit hyperactivity disorder, oppositional defiant and conduct disorders, depression, schizophrenia, and Tourette's syndrome.

CONCLUSIONS

Genetic findings will be helpful clinically in the elucidation of disordered brain processes, the understanding of nature-nurture interplay, diagnosis, genetic counselling, and pharmacotherapy.

The genetic epidemiology of psychiatric disorders: a current perspective

Psychiatric genetic epidemiology has, as a field, undergone considerable change in the last two decades. My goal here is to provide a brief, selective and inevitably personal overview of where the field has come from, where it is now and where it might be going. Methodologic issues will be emphasized, particularly those of an "epidemiologic" nature. I will organize this review around three of the major methods used in psychiatric genetics: family studies, twin studies and linkage studies.

Psychiatric disorders in the relatives of depressed probands. I. Comparison of prepubertal, adolescent and early adult onset cases

Research with adults suggests that early onset of depression is associated with increased rates of depression among relatives. This paper presents results, of a family study that tested the hypothesis that prepubertal depression was associated with a greater familial loading of depression than the postpubertal form, which in turn had a greater familial loading than adult onset depression. Probands were from a child to adult longitudinal study. Psychiatric disorders among relatives were assessed with family interview and family history methods 'blind' to all findings regarding the proband. Contrary to expectation, familial rates of depression did not differ significantly between the groups. However, manic disorders tended to be more common among the relatives of postpubertal depressed cases than among the relatives of adult onset cases. Moreover, relatives of prepubertal depressed subjects had higher rates of criminality and family discord than postpubertal subjects. Prepubertal onset depressive disorders appear to be relatively distinct from postpubertal forms.

A longitudinal study of stressful life events assessed at interview with an epidemiological sample of adult twins: the basis of individual variation in event exposure

This study investigates the basis of individual variation in exposure to stressful life events (SLEs). A population based sample of 547 MZ and 390 DZ female-female twin pairs, aged between 17 and 55 years, were surveyed by two structured interviews, separated by at least 1 year, that enquired about SLEs experienced during the preceding 12 months. Data were analysed with a model that resolves occasion specific ("random') versus enduring ("stable') influences on SLEs. The latter is partitioned into that due to genetic, familial environmental and unique environmental factors. We demonstrate that both random factors and stable individual differences underlie variation in self-reported exposure to SLEs. For most network events this stable variance makes a relatively small contribution to the total variance in SLEs exposure and is almost entirely due to genetic or familial environmental effects. Stable individual differences are more important determinants of personal SLEs, and these reflect both familial factors as well as previous experiences unshared by relatives.

Life events and personality in late adolescence: genetic and environmental relations

The relationship between life events and personality was investigated in the Minnesota Twin/Family Study, using 216 monozygotic and 114 dizygotic 17-year-old male twin pairs. Participants completed a life events interview designed for adolescents and the Multidimensional Personality Questionnaire. Life events were categorized into three types: life events to which all members of a family would be subject and those affecting an individual, which can be broadly construed as either nonindependent or independent. Univariate genetic model fitting indicated the presence of significant genetic effects (h2 = 49%) for nonindependent nonfamily life events but not for the other two types of life events. Bivariate genetic model fitting further confirmed that the significant phenotypic correlation between nonindependent life events and personality is in part genetically mediated. Specifically, the findings suggest that genetically influenced individual differences in constraint play a substantial role in life events whose occurrence is not independent of the individual's behavior.

Genetic influences on life events in childhood

Until recently, life events were considered as chance occurrences. However, there is now increasing evidence that reported life events, at least in adult life are not random. Life events not only tend to cluster in families but also appear to be influenced by genetic factors. The aim of this study was to investigate whether genetic factors also influence reported life events in childhood using a systematically ascertained sample of 376 twin pairs aged 8 to 17. Overall, reported life events in this younger population were found to be heritable. However, the degree of genetic and environmental influence appeared to vary across the sexes, at least for parent-rated life events and according to whether life events were rated by the parents or the children themselves. Genetic influences appeared to be more important for self reports, suggesting that individual differences in cognition play a role in reporting life events.

A critical review of recovered memories in psychotherapy: Part II--Trauma and therapy

OBJECTIVE

The clinical implications of the use of recovered memories in psychotherapy will be examined.

METHOD

The paper will review the relationship of trauma to psychopathology and discuss how traumatic histories might be dealt with in therapy.

RESULTS

Trauma is a risk factor for psychopathology, but is only one of many etiological factors in mental disorders. The search for recovered memories in psychotherapy could present dangers for patients.

CONCLUSIONS

The most reliable memories of trauma are those that have been present throughout the patient's life.

Mental retardation: genetic findings, clinical implications and research agenda

The most important genetic advances in the field of mental retardation include the discovery of the novel genetic mechanism responsible for the Fragile X syndrome, and the imprinting involved in the Prader-Willi and Angelman syndromes, but there have also been advances in our understanding of the pathogenesis of Down syndrome and phenylketonuria. Genetic defects (both single gene Mendelizing disorders and cytogenetic abnormalities) are involved in a substantial proportion of cases of mild as well as severe mental retardation, indicating that the previous equating of severe mental retardation with pathology, and of mild retardation with normal variation, is a misleading over-simplication. Within the group in which no pathological cause can be detected, behaviour genetic studies indicate that genetic influences are important, but that their interplay with environmental factors, which are also important, is at present poorly understood. Research into the joint action of genetic and environmental influences in this group will be an important research area in the future.

Behavioral genetics: concepts for research and practice in language development and disorders

This paper is an introduction to behavioral genetics for researchers and practitioners in language development and disorders. The specific aims are to illustrate some essential concepts and to show how behavioral genetic research can be applied to the language sciences. Past genetic research on language-related traits has tended to focus on simple etiology (i.e., the heritability or familiality of language skills). The current state of the art, however, suggests that great promise lies in addressing more complex questions through behavioral genetic paradigms. In terms of future goals it is suggested that: (a) more behavioral genetic work of all types should be done--including replications and expansions of preliminary studies already in print; (b) work should focus on fine-grained, theory-based phenotypes with research designs that can address complex questions in language development; and (c) work in this area should utilize a variety of samples and methods (e.g., twin and family samples, heritability and segregation analyses, linkage and association tests, etc.).

How heritability misleads about race

The Bell Curve revives and elaborates an argument given by Jensen to the effect that facts about heritability of IQ in whites dictate that blacks are genetically inferior in IQ. But clarification of the concept of heritability shows that this reasoning is fallacious. Heritability is an uninteresting measure that only misleads us about race.

The genetic epidemiology of self-esteem

BACKGROUND

Previous studies on self-esteem have focused exclusively on its psychosocial determinants. The goal of the present study is to clarify genetic v. environmental determinants of self-esteem.

METHOD

Participants were Caucasian women sampled from the Virginia Twin Register: 363 pairs of MZ and 238 pairs of DZ twins were available from the first wave of the study, and 430 pairs of MZ and 308 pairs of DZ twins from the second. Self-esteem was assessed with the Rosenberg's Self-Esteem Scale.

RESULTS

Using univariate twin analyses of self-esteem and a repeated measurement twin model, we found that self-esteem is a moderately heritable trait (heritability = 52% in the repeated measurement model); environmental influences are also very important, and are probably mostly not shared by members of a twin pair.

CONCLUSIONS

Aetiological models of self-esteem which examine only psychosocial factors are incomplete; genetic factors need to be integrated.

Mother-child interaction and the cognitive and behavioural development of four-year-old children with poor growth

A whole population inner-city survey identified 23 stunted, otherwise healthy, children with persistently poor growth from infancy to 4 years. Their cognitive development was significantly retarded relative to a matched comparison group. Unstructured home observations were used to create transcripts of verbal and nonverbal mother-child interactions. In both groups child behavioural adjustment was linked to maternal negativity, and cognitive performance was correlated with quality of stimulation. The developmental delay associated with chronic failure to thrive appeared more likely to arise from other influences, perhaps a previous biological insult, than to contemporaneous parenting practices.

Surface Area of Human Cerebral Cortex and Its Gross Morphological Subdivisions:In VivoMeasurements in Monozygotic Twins Suggest Differential Hemisphere Effects of Genetic Factors

We measured the surEdce area of the cerebral cortex and its gross morphological subdivisions in 10 pairs of monozygotic twins. Cortical surface area was estimated in vivo using magnetic resonance imaging and threedimensional computer models of the intra- and extrasulcal pial surface. The means and standard deviations of regional (e.g., gyral), lobar, hemisphere, and total cortical surface area were tabulated for the entire population of 20 young, right-handed adults (10 females, 10 males). To determine whether genotypic differences were associated with morphometric differences, analyses of variance were carried out on each measure across unrelated twin pairs (genotype factor) and within co-twins (birth order factor). Across unrelated pairs, there was wide variation in regional cortical surface area for the left hemisphere (normalized by total cortical surface area, p ≤ 0.0001) but not for the right hemisphere (normalized, p = 0.12). More variation in lobar surface area was also observed for the left hemisphere (normalized, p = 0.05) than for the right (normalized, p = 0.48). Within co-twins, no signifcant variation in regional surface area or lobar surface area was found for the left or right hemisphere. Although normalized regional and lobar surface area in the left hemisphere differed across unrelated pairs, overall left hemisphere surface area normalized by total cortical surface area did not (p = 0.73). Total cortical surface area normallzed by body weight varied across unrelated pairs (p = 0.001) but not within co-twins (p = 0.39). The effects observed across unrelated pairs were not attributable to sex differences.

These results suggest: 1) both the total area and folding of the cortical surface are heavily influenced by genetic factors in humans; and 2) the cerebral hemispheres may be differentially affected by genetic influences on cortical morphogenesis, with the languagedominant left cerebral cortex under stronger genetic control than the right.

Genetics and children's experiences in the family

Genetic research may have its greatest impact for clinicians and developmental researchers in terms of understanding the environment and how the environment relates to children's development. This review focuses on one example at the interface between nature and nurture. Recent research using diverse genetic designs shows that family environment as it is currently assessed involves a substantial contribution from genetic factors. Genetic factors also contribute to correlations between measures of the family environment and developmental outcomes. Implications of these findings are discussed.

Psychiatric genetics: research challenges and pathways forward

Lessons from past psychiatric genetic research, together with key issues in psychiatry requiring genetic investigation, are reviewed in order to consider the implications for the ways forward. It is argued that traditional quantitative genetics needs to use a combination of twin, adoptee, and family strategies, to examine continuities and discontinuities in psychopathology between childhood and adult life, to compare dimensions and categories, to employ adequate conceptualization and measurement of disorders, to use statistical techniques based on latent constructs, to use biological trait indicators where possible, to examine risk factors as well as diseases, to include good measures of postulated environmental risk variables, to study the interplay between genes and environment, and to study the key assumptions underlying genetic strategies. Molecular cytogenetics needs to consider both the general and specific psychopathological risks associated with chromosome abnormalities and to examine the mechanism involved, to examine the role of submicroscopic chromosomal deletions and of mitochondrial disorders, and to investigate the mechanisms involved in trinucleotide repeat amplifications that take place during intergenerational transmission. Molecular genetics needs to make greater use of smaller pedigrees in view of the concerns over phenotypic definition and genetic heterogeneity in very large extended dense pedigrees, to use sib-pair designs in view of the likelihood that most psychiatric disorder will prove to be multifactorial, to combine association strategies with linkage analyses, to pay careful attention to the definition of phenotypes in probands, to remain in close touch with other branches of biological psychiatry, and to make effective use of collaboration between centers. To date, transgenic models have had a rather limited application in psychiatry but, despite their difficulties, they are likely to provide an underpinning for gene therapy in disorders where that seems feasible.

The Emanuel Miller Memorial Lecture 1993. Genetic research and identification of environmental influences

As the importance of genetic influence in developmental psychopathology becomes widely accepted, we should not lose sight of the importance of genetic research for the investigation and identification of environmental influences. First, genetic research provides the best available evidence for the importance of nongenetic factors in behavioural development. Rarely does genetic influence account for more than half of the variance. Second, genetic research indicates that environmental effects on behavioural development largely involve nonshared environmental processes that make children in the same family different from one another. New research on this topic is presented and implications for research are discussed.

The genetic basis of complex human behaviors

Quantitative genetic research has built a strong case for the importance of genetic factors in many complex behavioral disorders and dimensions in the domains of psychopathology, personality, and cognitive abilities. Quantitative genetics can also provide an empirical guide and a conceptual framework for the application of molecular genetics. The success of molecular genetics in elucidating the genetic basis of behavioral disorders has largely relied on a reductionistic one gene, one disorder (OGOD) approach in which a single gene is necessary and sufficient to develop a disorder. In contrast, a quantitative trait loci (QTL) approach involves the search for multiple genes, each of which is neither necessary nor sufficient for the development of a trait. The OGOD and QTL approaches have both advantages and disadvantages for identifying genes that affect complex human behaviors.

Perceptions of nonshared childhood environment in bulimia nervosa

OBJECTIVE

The aim of this research was to identify perceptions of nonshared childhood environmental factors associated with bulimia nervosa and the comorbid personality traits associated with this disorder.

METHOD

Twenty-nine individuals with bulimia nervosa and 27 normal controls compared themselves to a sibling on a measure specifically designed to assess perceptions of nonshared environmental factors in parental, peer, and sibling relationships. Also, bulimic individuals' primary clinicians completed a series of ratings for each of the DSM-III personality disorders.

RESULTS

Bulimic individuals were more likely than controls to rate their fathers as showing less affection and more control toward them than toward their sibling. Among bulimic individuals, borderline personality disorder ratings were associated with the perception that both mother and father showed less affection toward the bulimic individual than toward her sibling. Avoidant and depressive personality ratings were associated with perceptions of unique experiences with peers.

CONCLUSION

These data provide preliminary evidence suggesting that the paternal relationship may be a source of nonshared environmental experience associated with bulimia nervosa. Borderline personality disorder among bulimics appears related to more pervasive within-family experiences across both the maternal and paternal relationship, while depressive and avoidant personality seems related to unique peer experiences.

Life events, social support and depression

This paper reviews current findings regarding social stress and support in clinical depression. Comparisons of recent life events at depressive onset and in general population controls show consistently raised event rates. The events span a range of threatening and undesirable experiences, with limited selectivity to exit events and interpersonal losses. Effects are similar in endogenous and non-endogenous symptom pictures, and there are suggestive findings in bipolar disorder, but these require further study. Events are also related to outcome and to relapse. Effects are moderate in degree, but relatively short-term of over six months to a year. For social support there are greater problems in the extent to which social support may be determined by the individual's own behaviour. Absence of social support appears to be associated with onset and relapse of depression, both acting independently and modifying effects of life events. Social stress findings have implications for prevention. The occurrence of major life events signals a period of increased risk when supportive interventions may prevent evolution of distress to disorder.