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

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.

Temperament and major depression in 11 to 16 year olds

Temperament (EAS teacher and parent questionnaire) and mental state (modified DISC-C interview with adolescent) was systematically assessed in 193 11 to 16 year olds (112 girls, 81 boys) screened for major depression in the community. Sex differences in the structure of temperament were noted from both parent and teacher reports. High (negative) emotionality alone was associated with major depression, particularly (but not exclusively) in girls.

The phenotypic and genetic relationships among measures of cognitive ability, temperament, and scholastic achievement

The covariance among measures of cognitive ability, temperament, and scholastic achievement was examined in a subsample of 326 (89 Monozygotic, 74 Dizygotic) twins drawn from the Western Reserve Twin Project. Both phenotypic and behavioral genetic models were fit to the data. Univariate analyses indicate significant genetic influences on cognitive, achievement, and temperament variables. Common environmental influences also affected cognition and achievement but not temperament. Multivariate analyses indicate that both genetic and common environmental influences contribute to the covariance among all three variables. Cognition and achievement are highly genetically correlated. In contrast, achievement and temperament are highly correlated for common environmentality, while cognition and temperament are not.

Depression in 11-16-year-old girls: the role of past parental psychopathology and exposure to recent life events

Interviews with parents of a non-referred sample of 11-16-year-old girls (n = 82) revealed that a significantly greater proportion of mothers with a lifetime history of any psychiatric disorder also reported one or more recent undesirable life events focused on the adolescent compared with mothers with no such history. Lifetime episodes of maternal depression and recent undesirable life events exerted significant additive effects on the likelihood of depression occurring in the previous 12 months in adolescent girls. Some families may be "life event prone" as a consequence of lifetime episodes of parental psychopathology.

Does reading make you smarter? Literacy and the development of verbal intelligence

The studies reported here represent the first steps in the development of a new research paradigm for studying the unique cognitive correlates of literacy. Reading experience exhibits enough isolable variance within a generally literate society to be reliably linked with cognitive differences. Research on such links is therefore facilitated because the consequences of engaging in literacy activities can be studied without necessarily obtaining totally illiterate samples or setting up cross-cultural comparisons. Issues that are at least analogous issues to those raised in cross-cultural research can be studied within literate societies with a paradigm such as this, and therefore the speed with which we can answer questions about the cognitive consequences of literacy may be greatly increased because more studies can be carried out, larger samples can be studied, and the range of the cognitive domains tapped can be widened. Research in this area appears to have been stifled because of the widespread acceptance of the most extreme interpretations of the outcome of Scribner and Cole's (1981) investigation--interpretations that have slowly diffused throughout the literature without being accompanied by any new data. These conclusions are fueled by a powerful social critique that advances the argument that the positive cultural and economic effects of literacy have been overstated--indeed, that literacy is, if anything, a repressive force (Auerbach, 1992; Street, 1984, 1988; Stuckey, 1991). Educational theorists such as Frank Smith accused the educational establishment of "overselling" literacy and have argued that "Literacy doesn't generate finer feelings or higher values. It doesn't even make anyone smarter" (1989, p. 354). The data reported herein appear to indicate that these theorists could well be wrong in this conclusion. If "smarter" means having a larger vocabulary and more world knowledge in addition to the abstract reasoning skills encompassed within the concept of intelligence, as it does in most laymen's definitions of intelligence (Stanovich, 1989; Sternberg, 1990), then reading may well make people smarter. Certainly our data demonstrate time and again that print exposure is associated with vocabulary, general knowledge, and verbal skills even after controlling for abstract reasoning abilities (as measured by such indicators as the Raven).(ABSTRACT TRUNCATED AT 400 WORDS)

Genetic contribution to risk of smoking initiation: comparisons across birth cohorts and across cultures

Self-report data on smoking initiation (whether the respondent admitted ever having smoked) were obtained from three large adult twin samples (Australia, N = 3,808 pairs; Virginia, N = 2,145 pairs; AARP, N = 3,620 pairs). Data were broken down into birth cohorts, and genetic models were fitted to test whether the decline, in more recent birth cohorts, in the percentage of individuals becoming smokers has led to a change in the relative contributions of genes and environment to risk of becoming a smoker. Despite a marked change in the proportion of male respondents who reported ever having smoked, we found no evidence for cohort differences in genetic and environmental effects (no Genotype x Cohort interaction). Significant differences in genetic and environmental parameters were found between sexes, and between the Australian and the two U.S. samples. In the U.S. samples, estimates of the genetic contribution to risk of becoming a smoker were 60% in men, 51% in women. In the Australian sample, heritability estimates were 33% in men, but 67% in women. Significant shared environmental effects on smoking initiation also were found, accounting for 23% of the variance in U.S. men, 28% of the variance in U.S. women, 39% of the variance in Australian men, and 15% of the variance in Australian women. In models that allowed for the environmental impact of cotwin smoking on a twin's risk of smoking initiation, estimates of the direct genetic contribution to risk of smoking initiation were comparable or higher (49-58% in U.S. women and 71% in Australian women; 58-61% in U.S. men, and 37% in Australian men).

An adoption and a cross-fostering study of the Minnesota Multiphasic Personality Inventory (MMPI) Psychopathic Deviate Scale

The first of two complementary studies compared biological and adoptive parents of teenage adoptees with either higher (n = 21) or low (n = 51) MMPI Psychopathic Deviate (Pd) scale scores. In comparison to biological mothers of the low-Pd adoptees, biological mothers of the high-Pd adoptees obtained significantly higher MMPI scores on six of eight clinical scales. Fewer differences existed between the corresponding groups of adoptive mothers, but adoptive mothers of the high Pd's did obtain significantly higher scores on the Pd and Hypomania scales. Substantial genetic correspondences also existed for Harris-Lingoes content subscales, with fewer correspondences between adoptees and their adoptive mothers. There were indications that adoptive mothers of the high-Pd children had personality traits which may have made them less effective in attenuating early signs of antisocial behavior. The second study employed a cross-fostering design dividing all biological and adoptive mothers (n = 138 each) by their respective median Pd raw scores to examine effects on offspring. Results confirmed the effect of biological mother Pd score, but only a trend suggested an adoptive mother effect, with no hint of an interaction.

Nature/nurture and the nature of nurture in the etiology of hypertension

Four reviews on the the role of developmental factors in hypertension are introduced and set in historical context. Recent research in the laboratory rat has shown that the preweaning environment makes an important contribution to the level of blood-pressure reached in adult life in genetic models of hypertension. Both of the most commonly used models of hypertension, the SHR and SS/Jr rat strains, exhibit lower BP in adult life, if they are fostered shortly after birth to mothers from their normotensive control strains. It has been suggested that it is the idiosyncratic maternal behavior of the hypertensive mothers which contributes to the elevated BP of their offspring, and it has been amply demonstrated that there is an association between a constellation of behaviors emitted by rat mothers and the adult BP of their offspring in a wide variety of genetic groups (inbred hypertensive animals, F1's and F2's). In addition to the above, maternal environment has been demonstrated to have a significant impact on the pathophysiological response of hypertensive animals to a high salt diet. Being raised by an SHR mother, versus an SS/Jr mother, increases the magnitude of BP increases to a high salt diet, susceptibility to hemorrhagic stroke, body weight loss and the risk of mortality. A variety of physiological systems are undergoing rapid change during the preweaning period and may mediate the effects of differences in the maternal environment. These include the renin-angiotensin system and the peripheral sympathetic nervous system. Nutritional factors may be involved in all of the phenomena referred to above. Thus, any physiological mechanisms that are proposed to link maternal behavior to its effects on the physiology of adult animals should recognize the involvement of nutritional factors. Research on the role of developmental factors such as maternal behavior in genetic models of hypertension is at the interface of two growing disciplines: behavior genetics and developmental psychobiology. The methodological and conceptual contributions of these fields to advancing our understanding of these phenomena is emphasized.

Psychosocial stressors: Concepts, causes and effects

Key advances in life events research included recognition of the need to differentiate events that were independent of disorder; to take the social context of events into account; to assess life events in terms of the long term threat rather than degree of life change; to determine the temporal linkage between life events and onset of psychiatric disorder; to appreciate the importance of long term difficulties as well as acute events; and to examine the role of vulnerability and protective mechanisms in determining individual differences in response to life events. Stress effects in childhood are considered in terms of possible mediating mechanisms; of turning points in life trajectory; of individual differences in response; of difficulties in the concept and measurement of onset of psychiatric disorder; of possible additivity of negative life events; and of the origins of individual differences in exposure to negative life experiences.

Parent-offspring and sibling adoption analyses of parental ratings of temperament in infancy and childhood

A first step toward understanding the etiology of personality is to investigate the relative impact of genetic and environmental factors using twin and adoption designs. Twin studies of infants and young children indicate substantial genetic influence for parental ratings of temperament in the preschool years. Adoption studies, however, have not previously been reported during the early years of life. We present parent-offspring comparisons for temperament (emotionality, activity, sociability, and impulsivity) for adopted and nonadopted children yearly from 1 to 7 years of age and their biological, adoptive, and nonadoptive parents. Also presented are correlations for adoptive and nonadoptive siblings when each child was 1, 2, 3, and 4 years of age. In contrast with twin results, little evidence is found for genetic influence. The average correlation between biological parents and their adopted-away children for data averaged over the 7 years is only .03. Similarly, the average parent-offspring correlation in nonadoptive families (.08) is no greater than in adoptive families (.12). Results for nonadoptive and adoptive siblings also indicate little genetic influence. The difference between the twin and adoption results may be due to environmental effects or to nonadditive genetic variance.

Quantitative trait loci and psychopharmacology: response to commentaries

The theme of our article was that a merger is needed between quantitative genetic and molecular genetic approaches in order to detect genes associated with psychopharmacological processes even when the genes account for small amounts of variance, so-called quantitative trait loci (QTL). The recombinant inbred (RI) QTL approach using the BXD RI series was discussed as a promising approach.The commentaries by Crabbe and by McGuffin and Buckland make several excellent points to which we have little to add. Goldman and Katz, on the other hand, disagree with some of our arguments and for this reason much of the limited space of our response to the commentaries is directed towards the commentary by Goldman and Katz. We focus on three general issues that they raise: the relationship between quantitative genetics and molecular genetics (single genes vs multiple genes), reverse genetics (anonymous markers) vs forward genetics (candidate genes) and heterogeneity (narrow vs broad assessment). Our response to Goldman and Katz is that these are false dichotomies-we do not need to choose sides between major- and multiple- gene approaches, reverse and forward genetics, or narrow and broad assessment. Rather than choosing sides, we should encourage the deployment of multiple research strategies in order to maximize the probability of identifying genes that affect behavior. A major strength of the RI QTL approach is that it can identify both major- and multiple-gene effects, it employs both reverse and forward genetics, and it can be applied to both narrow and broad assessment (and its multivariate extension is ideally suited to understanding the genetic interrelationships among different levels of assessment).After discussing these general issues raised by Goldman and Katz, we address two specific issues raised in the commentaries: multivariate analysis of multiple markers and the use of F(1) crosses between RI strains to increase power. We end by mentioning the establishment of an RI QTL collaborative registry which aims to facilitate RI QTL analyses.

Quantitative trait loci and psychopharmacology

Unlike simple Mendelian characteristics, individual differences in behavior, including behavioral responses to drugs, are generally distributed continuously, show substantial non-genetic as well as genetic influence, and appear to be influenced by many genes rather than one or two major genes. For these reasons, application of techniques of molecular biology to identify DNA sequences responsible for behavioral variation requires strategies that can detect genes that account for small amounts of variation, so-called quantitative trait loci (QTL). One such strategy involves analyses of association using recombinant inbred (RI) strains of mice. The RI QTL approach is especially valuable when researchers use the same RI series, such as BXD, which has 26 strains and more than 300 mapped genetic markers. Even when the progenitor inbred strains do not differ and when the strain distribution pattern of the RI strains is continuous, the approach can be used to identify and map QTL and estimate the extent to which the QTL account for genetic variance for a particular phenotype. A multivariate extension of this approach can assess genetic correlations among measures as well as the QTL underpinnings of these genetic correlations. The cumulative and integrative nature of such a program of research is the major benefit of the RI QTL approach for molecular genetic analysis of psychopharmacological processes, their physiological infrastructure, and their interface with other biological and behavioural systems.