Some currently available insecticides and their comparative efficacy on louse-infested, long-woolled sheep

The comparative efficacy of 13 of the sheep dips currently registered in New Zealand was investigated using sheep infested with the louse Bovicola ovis and carrying wool which was about 10 cm long at the shoulder. With the exception of one synthetic pyrethroid pour-on formulation, all products were able to effect a significant reduction in louse populations, relative to untreated controls, for 37 days after treatment. Only four products proved capable of eradicating lice and preventing their re-establishment up to 37 days after treatment. Variations in manufacturers' recommendations relating to the length of wool at dipping, and mode of application of dips are discussed in relation to the results.

An evaluation of two cypermethrin-based pour-on formulations on sheep infested with the biting louse,Bovicola ovis

Two synthetic pyrethroid (cypermethrin) based pour-on insecticide formulations, with high cis/trans isomer ratios (80:20) but differing in their respective active ingredient concentrations and solvent component(s), were applied to sheep infested with the biting-louse, Bovicola ovis. All treated sheep were penned with louse-infested sheep 9,12 and 15 weeks after the insecticide was applied. The 2% cypermethrin formulation achieved a higher level of control than the 1.25% cypermethrin formulation at each challenge interval when applied 12 weeks after shearing. The 2% cypermethrin formulation provided 97-100% control of lice from 4 to 16 weeks after application on sheep shorn 6 or 12 weeks prior to treatment. The 1.25% cypermethrin formulation provided 85% control of lice 4 weeks after application on sheep shorn 12 weeks prior to treatment, the level of control increasing to a maximum of 100% by week 9, and declining thereafter. The 2% cypermethrin formulation may provide a better level of control in long-woolled sheep than 1.25% cypermethrin, by compensating for the diluent effect of lipid.

Major depression and generalized anxiety disorder. Same genes, (partly) different environments?

Bivariate twin analysis can determine the extent to which two disorders share common genetic, familial environmental, or individual-specific environmental risk factors. We applied this method to lifetime diagnoses of major depression and generalized anxiety disorder as assessed at personal interview in a population-based sample of 1033 pairs of female same-sex twins. Three definitions of generalized anxiety disorder were used that varied in minimum duration (1 vs 6 months) and in the presence or absence of a diagnostic hierarchy. For all definitions of generalized anxiety disorder, the best-fitting twin model was the same. Familial environment played no role in the etiology of either condition. Genetic factors were important for both major depression and generalized anxiety disorder and were completely shared between the two disorders. A modest proportion of the nonfamilial environmental risk factors were shared between major depression and generalized anxiety disorder. Within the limits of our statistical power, our findings suggest that in women, the liability to major depression and generalized anxiety disorder is influenced by the same genetic factors, so that whether a vulnerable woman develops major depression or generalized anxiety disorder is a result of her environmental experiences.

Bulimia nervosa and major depression: a study of common genetic and environmental factors

A genetic analysis of the co-occurrence of bulimia and major depression (MD) was performed on 1033 female twin pairs obtained from a population based register. Personal interviews were conducted and clinical diagnoses made according to DSM-III-R criteria. Additive genes, but not family environment, are found to play an important aetiological role in both bulimia and MD. The genetic liabilities of the two disorders are correlated 0.456. While unique environmental factors account for around half of the variation in liability to both bulimia and MD, these risk factors appear to be unrelated, i.e., each disorder has its own set of unique environmental risk factors. Thus, the genetic liability of bulimia and MD is neither highly specific nor entirely non-specific. There is some genetic correlation between the two disorders as well as some genetic and environmental risk factors unique to each disorder. Limitations and directions for future research are discussed.

Evidence for genetic influences on personality from self-reports and informant ratings

Self-report data on Extraversion (E) and Neuroticism (N), together with ratings by the co-twin, were obtained from a sample of 826 adult female twin pairs ascertained through a population-based twin register. Data were analyzed using a model that allowed for the contributions to personality ratings of the rater's personality (rater bias) as well as of the personality of the person being rated. For E, but not for N, significant rater bias was found, with extraverted respondents tending to underestimate, and introverted respondents tending to overestimate, the Extraversion of their co-twins. Good agreement between self-reports and ratings by the respondent's co-twin was found for both E and N. Substantial genetic influences were found for both personality traits, confirming findings from genetic studies of personality that have relief only on self-reports of respondents.

Pathways to hysterectomy: insights from longitudinal twin research

OBJECTIVE

We hypothesized that genetic influences act on "liability" to hysterectomy, that secular influences might differentially affect relative importance of genetic and environmental influences, and that the sources of genetic influences could be identified from reported risk factors.

STUDY DESIGN

Hysterectomy data from an Australia-wide volunteer sample of female adult monozygotic and dizygotic twins are reported. In 1980 through 1982 a mailed questionnaire was completed by 1232 monozygotic female twin pairs and 751 dizygotic female twin pairs (3966 women) from the Australian Twin Register (wave 1). The same twins were surveyed by questionnaire 8 years later (wave 2).

RESULTS

A total of 366 had undergone hysterectomy by wave 1 and a further 198 at wave 2. The twin-pair correlations for liability to hysterectomy at wave 1 (0.61 +/- 0.06 for monozygotic and 0.20 +/- 0.11 for dizygotic) and wave 2 (0.65 +/- 0.05 for monozygotic and 0.32 +/- 0.09 for monozygotic) indicated a substantial genetic contribution. Reported risk factors accounted for only 15% of total variance.

CONCLUSION

Genetic influences on liability to hysterectomy were substantial and stable across birth cohorts, but the important sources of genetic influence on liability to hysterectomy are yet to be identified.

Genetic differences in psychomotor performance decrement after alcohol: a multivariate analysis

We reanalyzed data on the decline in performance on a battery of psychomotor tests, after a standard dose of ethanol (0.75 g/kg body weight), of 206 same-sex twin pairs. Principal components analysis identified two orthogonal factors. The first factor was strongly associated with increased body sway, self-rated intoxication and unwillingness to drive, and reported low average weekly alcohol consumption, but showed a very weak association with blood alcohol concentration. The second factor had high loadings on tests assessing psychomotor coordination, was strongly associated with blood alcohol concentration, but was unrelated to willingness to drive or self-rated intoxication. Multivariate genetic analysis indicated independent genetic and environmental determination of differences in sensitivity to the effects of alcohol on these two factors.

Generalized anxiety disorder in women. A population-based twin study

Little is known about the role of familial and genetic factors in the etiology of generalized anxiety disorder (GAD), a new disorder first proposed in DSM-III. We examine this question in 1033 female-female twin pairs from a population-based registry. Both members in each twin pair were "blindly" assessed by structured psychiatric interview. Our results suggest the following: (1) GAD is a moderately familial disorder; (2) the tendency for GAD to run in families seems to be due largely or entirely to genetic factors shared between relatives rather than to the effects of the familial environment; (3) the heritability of GAD, estimated at around 30%, is modest, with the remainder of the variance in liability resulting from environmental factors not shared by adult twins; (4) the heritability of GAD cannot be explained solely by the occurrence of GAD only during episodes of major depression or panic disorder; and (5) the etiologic role of genetic factors is probably similar in GAD with a 1- vs a 6-month minimum duration of illness.

A population-based twin study of major depression in women. The impact of varying definitions of illness

Although depression aggregates in families, the degree to which this aggregation results from genetic vs environmental factors remains uncertain. We examined this question in 1033 female-female twin pairs from a population-based registry. Both members of each twin pair were "blindly" assessed by structured psychiatric interview. Nine commonly used definitions of major depression, which produced life-time prevalence rates ranging from 12% to 33%, were examined. For all definitions, the results of model fitting to twin correlations suggested that the liability to depression results from genetic factors and environmental experiences unique to the individual. For seven of the definitions, the estimated heritability of liability was similar, ranging from 33% to 45%. For the two definitions that included only primary cases of depression, the heritability was lower (21% to 24%). The results document that in women (1) genetic factors play a substantial, but not overwhelming, role in the cause of depression; (2) the tendency for depression to aggregate in families results largely from shared genetic and not from shared environmental factors; (3) except for definitions that exclude secondary cases, the magnitude of genetic influence is similar in broadly and narrowly defined forms of major depression; and (4) most environmental experiences of causative importance for depression are those not shared by members of an adult twin pair.

The genetic epidemiology of phobias in women. The interrelationship of agoraphobia, social phobia, situational phobia, and simple phobia

In 2163 personally interviewed female twins from a population-based registry, the pattern of age at onset and comorbidity of the simple phobias (animal and situational)--early onset and low rates of comorbidity--differed significantly from that of agoraphobia--later onset and high rates of comorbidity. Consistent with an inherited "phobia proneness" but not a "social learning" model of phobias, the familial aggregation of any phobia, agoraphobia, social phobia, and animal phobia appeared to result from genetic and not from familial-environmental factors, with estimates of heritability of liability ranging from 30% to 40%. The best-fitting multivariate genetic model indicated the existence of genetic and individual-specific environmental etiologic factors common to all four phobia subtypes and others specific for each of the individual subtypes. This model suggested that (1) environmental experiences that predisposed to all phobias were most important for agoraphobia and social phobia and relatively unimportant for the simple phobias, (2) environmental experiences that uniquely predisposed to only one phobia subtype had a major impact on simple phobias, had a modest impact on social phobia, and were unimportant for agoraphobia, and (3) genetic factors that predisposed to all phobias were most important for animal phobia and least important for agoraphobia. Simple phobias appear to arise from the joint effect of a modest genetic vulnerability and phobia-specific traumatic events in childhood, while agoraphobia and, to a somewhat lesser extent, social phobia result from the combined effect of a slightly stronger genetic influence and nonspecific environmental experiences.

Genetic and environmental factors in the aetiology of menstrual, premenstrual and neurotic symptoms: a population-based twin study

Symptoms during the premenstrual and menstrual phases of the female reproductive cycle were assessed in 827 pairs of female same-sex twins from a population-based registry. By conventional factor analysis, premenstrual and menstrual symptoms were relatively independent of one another and of baseline 'neurotic' symptoms (i.e. anxiety, depression and somatization). Familial resemblance for menstrual and premenstrual symptoms was due solely to genetic factors with heritability estimates of 39.2% and 35.1%, respectively. Multivariate genetic analysis revealed distinct genetic and environmental factors for menstrual, premenstrual and neurotic symptoms. The genes and individual-specific experiences that predispose to premenstrual symptoms appear to be largely distinct from those which predispose either to menstrual or to neurotic symptoms. The generalizability of these results may be limited because only a modest number of premenstrual and menstrual symptoms were assessed, all by retrospective self-report.

Childhood parental loss and adult psychopathology in women. A twin study perspective

We examine the relationship between parental loss prior to age 17 years and adult psychopathology in 1018 pairs of female twins from a population-based registry. The relationship between loss and adult psychopathology varied as a function of the kind of loss (death vs separation), the parent involved, and the form of psychopathology. Increased risk for major depression and generalized anxiety disorder was associated with parental separation but not parental death and with separation from either mother or father. Panic disorder was associated with parental death and maternal, but not paternal, separation. Increased risk for phobia was associated with parental death and not parental separation. Risk for eating disorder was unrelated to the experience of parental loss. A model that includes parental loss as a form of "specified" family environment shows that, if it is truly an environmental risk factor for adult psychopathologic conditions, it can account for between 1.5% and 5.1% of the total variance in liability to these disorders and is responsible for between 7.0% and 20.5% of the tendency for these disorders to aggregate in siblings.

Using multidimensional scaling on data from pairs of relatives to explore the dimensionality of categorical multifactorial traits

An accurate specification of the dimensionality and ordering of categorical multifactorial phenotypes (e.g., smoking status, including heavy, moderate, light, and nonsmokers) is an important prerequisite for the genetic analysis of these traits. Typically, phenotypic dimensionality and ordering are determined by comparing the relative fits of alternative parametric threshold models. Here, a method of analysis is described which addresses the same issue of trait dimensionality but does not require parametric assumptions. Specifically, we detail how nonmetric multi-dimensional scaling (MDS), applied to contingency tables which cross-classify the phenotypes or responses of one relative with another, may be used to explore trait dimensionality. Scaling results from deterministic simulation studies indicate that the latent structure of categorical phenotypes can be recovered with nonmetric MDS. Results from stochastic simulations, however, indicate that the accuracy of recovery, as well as the rejection of models of incorrect dimensionality, are strongly dependent upon sample size and the latent liability correlation between relatives. As an application of the method, the dimensionality of a measure of smoking status in 1,656 pairs of monozygotic twins ascertained through the American Association of Retired Persons is considered. The MDS results indicate that the onset of the smoking habit and the quantity smoked in this aging population represent a unidimensional process. The implication this finding has for subsequent genetic analysis is discussed.

Evidence for genetic influences on personality from self-reports and informant ratings

Self-report data on Extraversion (E) and Neuroticism (N), together with ratings by the co-twin, were obtained from a sample of 826 adult female twin pairs ascertained through a population-based twin register. Data were analyzed using a model that allowed for the contributions to personality ratings of the rater's personality (rater bias) as well as of the personality of the person being rated. For E, but not for N, significant rater bias was found, with extraverted respondents tending to underestimate, and introverted respondents tending to overestimate, the Extraversion of their co-twins. Good agreement between self-reports and ratings by the respondent's co-twin was found for both E and N. Substantial genetic influences were found for both personality traits, confirming findings from genetic studies of personality that have relief only on self-reports of respondents.

Religion and education as mediators of attitudes: a multivariate analysis

The transmission of social attitudes has been investigated as a possible model of cultural inheritance in a sample of 3810 twin pairs from the Australian National Health and Medical Research Twin Registry. Six social attitude factors were identified and univariate genetic models fitted to scores on each factor. A joint multivariate genetic analysis of the six attitude factors, church attendance, and education indicated that the attitudes were correlated--the same genes and shared environments influenced more than one attitude factor. A current controversy regarding social attitudes is whether the significant loadings on this shared environmental component represent true cultural influences or are actually the genetic consequences of phenotypic assortative mating for church attendance and educational attainment (Martin et al., 1986). In our data, church attendance is almost entirely due to the impact of the shared environment. The large shared environmental component on church attendance also accounts for a substantial part of the family resemblance in social attitudes, suggesting that not all of the apparent cultural effects found in earlier studies can be ascribed to the genetic effects of assortative mating. However, church attendance and education do not completely account for the cultural component. Therefore, effects in addition to church attendance, education, and assortative mating for church attendance and education must be involved in the cultural component of the inheritance of attitudes.

The family history method: whose psychiatric history is measured?

OBJECTIVE

The family history method, in which an informant is asked about the history of psychiatric illness in relatives, is widely used in psychiatric research. Previous research has examined the influence on family history information of characteristics of the relative. In this report, the authors seek to clarify the impact on family history reporting of the psychiatric history of the informant.

METHOD

Both members of female twin pairs from a population-based twin registry were asked about the history of major depression, generalized anxiety disorder, and alcoholism in their mother and father. The authors examined twin pairs discordant for each of the three diagnoses and predicted that the affected twin would report higher rates of the same disorder in her parent than would the unaffected twin.

RESULTS

Twins with a history of major depression or generalized anxiety disorder but not twins with alcoholism were significantly more likely to report the same disorder in their parents than were their unaffected co-twins.

CONCLUSIONS

For major depression and generalized anxiety disorder, a family history diagnosis appears to reflect the psychiatric history of both the relative and the informant. Caution may be needed in the interpretation of results based on the family history method, although the magnitude of this problem may be attenuated by the use of multiple informants.

The inheritance of alcohol consumption patterns in a general population twin sample: II. Determinants of consumption frequency and quantity consumed

Genetic models were fitted to self-report data on frequency of alcohol consumption and average quantity consumed when drinking, from 3,810 adult Australian twin pairs. Frequency of consumption is determined both by an abstinence dimension, which is strongly influenced by shared environmental effects but not by genetic effects, and by an independent frequency dimension, which is influenced by genetic effects in both sexes and possibly by shared environmental affects in men. Quantity of alcohol consumed is likewise determined by an environmental abstinence dimension and by an independent and partly heritable quantity dimension. The best-fitting model allowed for two routes to abstinence: those who were not abstainers by virtue of their position on the abstinence dimension could nonetheless become abstainers by their position on the second, frequency (or quantity) dimension. Heritability estimates were 66% in women and 42-75% in men, for frequency; and 57% in women and 24-61% in men, for quantity.

The inheritance of alcohol consumption patterns in a general population twin sample: I. Multidimensional scaling of quantity/frequency data

Quantity/frequency data on alcohol consumption were obtained by mailed questionnaire from 2,903 same-sex monozygotic and dizygotic Australian twin pairs. Nonmetric multidimensional scaling was applied to these data. A three-dimensional solution was required to account for the observed pattern of twin concordances for alcohol consumption. These results suggest separate determination of abstinence, frequency of consumption and quantity consumed when drinking, rather than inheritance of a single continuum of overall consumption level.

Estimating genetic influences on the age-at-menarche: a survival analysis approach

A survival analysis regression model is described for analyzing twin data on the age-at-menarche. The model includes latent genetic and environmental covariates and allows one to test hypotheses regarding the nature of familial aggregation for age-at-onset. Additionally, the model accommodates a variety of baseline survival distributions and therefore may be used to test different developmental hypotheses. Model-fitting results indicate that a survival model with a baseline gamma distribution gives an adequate fit to recalled age-at-menarche of 1,888 pairs of Australian female monozygotic and dizygotic twins. Further, results show that additive genetic and dominance genetic effects contribute to shared variation in age-at-menarche. If there are common environmental influences on the timing of menarche, they are completely obscured by nonadditivity in genetic factors, and information from other relationships would be required to detect their effect.

Coping: a genetic epidemiological investigation

This study examines data on self-report coping behaviour, life events and symptoms of anxiety and depression in a general population sample of 827 female twin pairs. Factor analysis identified three almost uncorrelated coping factors: turning to others; problem solving; and denial. Turning to others and problem solving were negatively and denial was positively related to levels of anxiety and depression. Turning to others and problem solving buffered the depressogenic and anxiogenic effects of stressful life events, while denial exacerbated the anxiogenic effects of life events. Structural equation model-fitting indicated that twin resemblance in turning to others and problem solving could be explained entirely by genetic factors with an estimated heritability of 30 and 31%, respectively. For denial, twin resemblance could be best explained by familial-environmental factors accounting for 19% of the total variation. Genes may affect the vulnerability to psychiatric disorders in part by influencing coping behaviour.

Intoxication after an acute dose of alcohol: an assessment of its association with alcohol consumption patterns by using twin data

We examined the hypothesis that genetically determined differences in sensitivity to alcohol explain some of the genetic variation in alcohol consumption pattern. Self-report data on average weekly alcohol consumption and self-ratings of intoxication after a standard dose of ethanol (0.75 g/kg body weight), used as an index of sensitivity, were obtained on 206 Australian twin pairs. Significant genetic covariance between weekly consumption and level of intoxication after alcohol intake was found in males, lower ratings of intoxication being associated with increased consumption. However, when direction of causation models were fitted to the male twin data, the hypothesis that decreased sensitivity was a cause of increased consumption was rejected. The major causal effect was that of weekly consumption on level of sensitivity. A similar, although nonsignificant, trend was observed in females. The strength of the association between self-report of average weekly consumption and level of intoxication after a standard dose of alcohol supports the validity of the former measure.

Personality and reproductive fitness

The relationship between reproductive success (number of biological children) and personality was explored in 1101 postmenopausal females from the Australian twin registry. The quadratic response surface relating fitness to extraversion (E) and neuroticism (N) showed a saddle point at intermediate levels of E and N. Selection was shown to be stabilizing, i.e., having an intermediate optimum, along the axis low E, low N-high E, high N and more mildly disruptive, having greater fitness in the extremes, along the axis low N, high E-high N, low E. Neither dimension of personality considered by itself showed a significant linear or quadratic relationship to reproductive success. Sections through the fitness surface, however, show selection tends to favor high neuroticism levels in introverts and low neuroticism levels in extroverts.

Evidence for genetic influences on sleep disturbance and sleep pattern in twins

The etiologic role of genotype and environment in sleep pattern (daytime napping, habitual bedtime, and sleep duration) and subjective sleep quality and sleep disturbance was examined using a general population sample of 3,810 adult Australian twin pairs, aged 17-88 years. Genetic differences accounted for at least 33% of the variance in sleep quality and sleep disturbance and 40% of the variance in sleep pattern. There was no evidence for a decline in the importance of genetic predisposition with age. Short-term environmental fluctuations accounted for as much as 30% of the variance, and more stable nonfamilial environmental effects accounted for the remainder. No effect of shared family environment on sleep characteristics was found.

Religious affiliation in twins and their parents: testing a model of cultural inheritance

The transmission of religious affiliation is analyzed in a sample of 3810 Australian twin pairs and their parents. Twins were classified by sex, zygosity, and whether they were living together or apart. Analysis of twin, spousal, and parent-offspring resemblance shows that several different forms of cultural inheritance operate jointly in the transmission of religious affiliation. Model-fitting methods show that (1) the environmental influence of mothers is significantly greater than fathers; (2) there is a substantial amount of assortative mating for religious affiliation; (3) there is a substantial environmental component shared by twins which does not depend on parental religious affiliation; (4) religious affiliation attributed to parents by their children is biased by the religious affiliation of the children; (5) nongenetic effects on the expression of religious affiliation are much greater in twins living together; and (6) a moderate genetic effect on religious affiliation is expressed in females but only when twins live apart. Implications of the method and findings are discussed for other aspects of family resemblance, including the analysis of social and occupational mobility.

Psychoticism as a dimension of personality: A multivariate genetic test of Eysenck and Eysenck's psychoticism construct

In this study, we applied multivariate genetic analysis, a generalization of factor analysis and behavior genetic analysis, to responses to items of the Psychoticism scale of the Eysenck Personality Questionnaire by 2,903 adult same-sex Australian twin pairs. Item loadings on genetic, shared environmental, and nonshared environmental common and specific factors were estimated. The genetic factor structure differed considerably from the environmental structures, particularly in men. The genetic correlation between suspiciousness items and items reflecting unconventional or tough-minded attitudes or hostility to others was negative, but the environmental correlation was positive. Thus, conventional behavior genetic studies that have reported significant heritability of psychoticism, on the basis of analyses of scale scores, are misleading as to what trait is being inherited.