Genetic and environmental influences on sexual orientation and its correlates in an Australian twin sample

We recruited twins systematically from the Australian Twin Registry and assessed their sexual orientation and 2 related traits: childhood gender nonconformity and continuous gender identity. Men and women differed in their distributions of sexual orientation, with women more likely to have slight-to-moderate degrees of homosexual attraction, and men more likely to have high degrees of homosexual attraction. Twin concordances for nonheterosexual orientation were lower than in prior studies. Univariate analyses showed that familial factors were important for all traits, but were less successful in distinguishing genetic from shared environmental influences. Only childhood gender nonconformity was significantly heritable for both men and women. Multivariate analyses suggested that the causal architecture differed between men and women, and, for women, provided significant evidence for the importance of genetic factors to the traits' covariation.

Further evidence against the environmental transmission of individual differences in neuroticism from a collaborative study of 45,850 twins and relatives on two continents

We examine the hypothesis that environmental transmission is a significant factor in individual differences for Neuroticism among 45,850 members of extended twin kinships from Australia (N = 20,945) and the United States (N = 24,905). To this large data set we fitted a model estimating genetic and environmental components of variance and gene-environmental covariance to examine the causes of individual differences in Neuroticism. For the combined sample we reject models including environmental transmission, shared environment, and a special twin environment in favor of more parsimonious genetic models. The best-fitting model involved only modest assortative mating, nonshared environment, and both additive and nonadditive genetic components. We conclude, first, that there is no evidence for environmental transmission as a contribution to individual differences in Neuroticism in these replicated samples, drawn from different continents, and, second, that a simple genetic structure underlies familial resemblance for the personality trait of Neuroticism. It is interesting that, despite the opportunity provided by the elaborate design and extensive power of our study, the picture revealed for the causes of individual differences in Neuroticism is little more complex than that found from earlier, simpler designs applied to smaller samples. However, this simplicity could not have been confirmed without using a highly informative design and a very large sample.

CYP17 promotor polymorphism and ovarian cancer risk

The CYP17 gene encodes the cytochrome P450c17alpha enzyme, which functions at 2 different points in the steroid biosynthesis pathway, and is considered a candidate susceptibility gene for endocrine-related tumors. A T to C substitution polymorphism exists in the 5' promoter region of this gene, and creates an additional Sp1-type motif. Several studies have examined this polymorphism as a risk factor for breast cancer, but results have been conflicting. We examined 319 cases of ovarian cancer and 298 unaffected controls for the T-C polymorphism. There was no significant difference between cases and controls for the allele frequencies (p = 0.6), or for genotype distribution (p = 0.9). The odds ratio (95% confidence interval) for ovarian cancer was 1.13 (0.70-1.82) for the putative "cancer susceptibility" CC genotype and 1.07 (0.77-1.48) for any C allele (CC or CT genotype). Results were little different after adjustment for age. Stratification of the ovarian cancer cases according to form (benign, low malignant potential or invasive), histology, grade or stage failed to reveal any heterogeneity with respect to CYP17 genotype. Our data provide no evidence for an association between ovarian cancer risk and the genotype defined by the CYP17 5' promoter region T-C polymorphism.

Effects of HFE C282Y and H63D polymorphisms and polygenic background on iron stores in a large community sample of twins

The aim of this study was to assess and to compare the role of HFE polymorphisms and other genetic factors in variation in iron stores. Blood samples were obtained from 3,375 adult male and female twins (age range 29-82 years) recruited from the Australian Twin Registry. There were 1,233 complete pairs (562 monozygotic and 571 dizygotic twins). Serum iron, transferrin, transferrin saturation with iron, and ferritin were measured, and the HFE C282Y and H63D genotypes were determined. The frequency of the C282Y allele was.072, and that of the H63D allele was.141. Significant sources of variation in the indices of iron status included age, sex, age-sex interaction, body-mass index, and both the C282Y and H63D genotypes. The iron, transferrin, and saturation values of CC and CY subjects differed significantly, but the ferritin values did not. After correction for age and body-mass index, 23% and 31% of the variance in iron, 66% and 49% of the variance in transferrin, 33% and 47% of the variance in transferrin saturation, and 47% and 47% of the variance in ferritin could be explained by additive genetic factors, for men and women, respectively. HFE C282Y and H63D variation accounted for <5% of the corrected phenotypic variance, except for saturation (12% in women and 5% in men). We conclude that HFE CY and HD heterozygotes differ in iron status from the CC and HH homozygotes and that serum transferrin saturation is more affected than is serum ferritin. There are highly significant effects of other as-yet-unidentified genes on iron stores, in addition to HFE genotype.

Do individual differences in sociosexuality represent genetic or environmentally contingent strategies? Evidence from the Australian twin registry

Although men are substantially more interested than women in casual sex, there is ample variation in this trait (sociosexuality) within both sexes. One theory hypothesizes that within-sex sociosexual variation results from genetic variation maintained by frequency-dependent selection. If so, sociosexuality should be substantially heritable. A competing theory is that children acquire their mating strategy after observing their parents' relationship. By this theory, sociosexuality should reveal a strong shared environmental component. The authors studied genetic and environmental influences on sociosexuality using a large, representative volunteer twin sample. Parental marital instability was modestly associated with sociosexuality, but this could have been due to either genetic or environmental factors. Consistent with genetic theory, familial resemblance appeared primarily due to additive genetic rather than shared environmental factors.

Monoamine oxidase: associations with alcohol dependence, smoking and other measures of psychopathology

BACKGROUND

Many reports have appeared on associations between platelet monoamine oxidase (MAO) activity and susceptibility to psychiatric conditions; principally alcohol dependence but also conduct disorder, other drug use and depression. Recently, it has become apparent that MAO activity is inhibited by some component of cigarette smoke, and smokers have low platelet MAO activity. Since the prevalence of smoking is higher in many of the conditions in which MAO has been implicated, the MAO susceptibility associations may be partly, or entirely, false.

METHODS

We have measured platelet MAO in 1551 subjects, recruited from the Australian NHMRC Twin Registry, who have provided information on alcohol use and dependence, smoking, conduct disorder, depression, attempted suicide, panic disorder and social phobia.

RESULTS

Current smoking reduced platelet MAO activity in a significant and dose-related manner, with no evidence of lower MAO in ex-smokers or in non-smoking subjects with co-twins who smoked. Alcohol use and lifetime DSM-III-R alcohol dependence history were not associated with MAO activity when smoking was taken into account. Depression, panic disorder and social phobia showed no significant associations with platelet MAO activity. Subjects with a history of serious attempts at suicide had low platelet MAO activity; but although the difference from controls was as great as the reduction associated with smoking it was not significant after correction for smoking effects.

CONCLUSIONS

Although synaptic MAO activity undoubtedly plays a role in psychopathology, the concept that platelet MAO activity is a direct genetic marker of vulnerability to alcohol dependence cannot be sustained.

Genetic and environmental influences on sexual orientation and its correlates in an Australian twin sample

We recruited twins systematically from the Australian Twin Registry and assessed their sexual orientation and 2 related traits: childhood gender nonconformity and continuous gender identity. Men and women differed in their distributions of sexual orientation, with women more likely to have slight-to-moderate degrees of homosexual attraction, and men more likely to have high degrees of homosexual attraction. Twin concordances for nonheterosexual orientation were lower than in prior studies. Univariate analyses showed that familial factors were important for all traits, but were less successful in distinguishing genetic from shared environmental influences. Only childhood gender nonconformity was significantly heritable for both men and women. Multivariate analyses suggested that the causal architecture differed between men and women, and, for women, provided significant evidence for the importance of genetic factors to the traits' covariation.

Prevalence of gyrA, gyrB, parC, and parE mutations in clinical isolates of Streptococcus pneumoniae with decreased susceptibilities to different fluoroquinolones and originating from Worldwide Surveillance Studies during the 1997-1998 respiratory season

From 8,419 worldwide clinical isolates of Streptococcus pneumoniae obtained during 1997-1998, 69 isolates with reduced susceptibility or resistance to fluoroquinolones (FQs) were molecularly characterized. For the isolates in this prevalence study, only parC (Ser-79-->Tyr) and gyrA (Ser-81-->Phe or Tyr) mutations, especially in combination, were found to contribute significantly to resistance. These mutations influenced the FQ MICs to varying degrees, although the rank order of activity remains independent of mutation type, with ciprofloxacin the least active, followed by levofloxacin, gatifloxacin/grepafloxacin/moxifloxacin/sparfloxaci n/trovafloxacin, and clinafloxacin/sitafloxacin. Efflux likely plays a crucial role in reduced susceptibility for new hydrophilic FQs.

Dimensions of psychological masculinity-femininity in adult twins from opposite-sex and same-sex pairs

Male and female twins with opposite-sex co-twins were compared to twins with same-sex co-twins on three independent dimensions of masculinity-femininity, in order to examine the hypothesis that the hormones of the co-twin might have an effect on prenatal masculinization. The analysis was originally carried out for an older cohort from the Australian Twin Registry (2647 pairs, mean age 41.2), and then repeated in a younger cohort (1503 pairs, mean age 23.2). For women, the results on two of the three scales support and extend that of an earlier large study in Finland by Rose et al. (1994), who found no effect of sex of co-twin on feminine interests. One of the two scales contrasted worried and calm individuals, the other, confiding and reserved ones. The third scale, willingness to break or bend rules, showed a small effect of shared environmental influence, and it lay in the expected direction for a prenatal hormonal effect--females with a male co-twin scored higher (more like males). Most previous studies have not looked at the effect of sex of co-twin on males. The present study detected several such effects, although all were small in magnitude. The pattern was complex: sometimes the effect was in the masculine direction, sometimes in the feminine direction; sometimes there was agreement between the older and younger cohorts, sometimes not. Overall, the results suggest that no simple masculinization hypothesis--prenatal or postnatal--will adequately account for all the evidence. Age, sex, and aspect of masculinity-femininity must be taken into account.

Interface dimensions of CEREC-2 MOD inlays

OBJECTIVES

To quantify the width of the cement interface between ceramic inlays generated by the CEREC-2 CAD-CAM system and the tooth, and to determine the effect of cement viscosity on the interface width.

METHODS

Standardised MOD cavities were cut in 15 human premolar teeth using a custom paralleling device. A ceramic inlay was made with a CEREC-2 CAD-CAM machine for each tooth. The inlays were cemented using one of three resin-based composite systems of varying viscosity; a hybrid microfilled posterior composite, a compomer restorative and a dual-cure luting composite. The teeth were subsequently sectioned and measurements were taken at 21 key points with the aid of an image-analysis light microscopy system.

RESULTS

Statistical significance tests were applied to examine for difference in interface dimensions at specific points within each of the cement-groups and amongst groups. The interface space at the occlusal walls has a distinct wedge shape, being narrower at the external interface (50 microns, SD 15) than internally (211 microns, SD 38). There is no statistically significant difference in the interface dimensions of the gingival floor between the boxes that lie above and below the CEJ. There is no statistically significant difference in the width of the interface at any given point between the three cement groups.

SIGNIFICANCE

There is a significant improvement in the fit of CEREC-2 restorations when compared with the original CEREC system. Cements of varying viscosity (within the measured range) may be used for cementation of these inlays, without adversely affecting the width of the interface. Caution must be exercised with light-activated composite cements to ensure adequate transmission of light through the ceramic and the underlying composite cement.

Birth weight and age at menopause in Australian female twin pairs: exploration of the fetal origin hypothesis

In a twin sample where duration of gestation can be controlled, a specific example of the fetal origins hypothesis concerning association between low birth weight and early age at menopause is explored. The hypothesis is based on the physiologically plausible path from intrauterine growth retardation and reduced numbers of primary follicles to an earlier menopause. The sample comprised 323 Australian female twin pairs where both co-twins had reached menopause naturally and reported on their weight at birth. Regression analysis showed no linear association between the two variables (P = 0.371, r(2) = 0.0009). Intra-pair differences in age at menopause were investigated in the context of relative birth weight of co-twins. In 265 pairs an intra-pair birth weight difference was reported. In monozygotic (MZ) pairs (n = 168) this allowed for control of genetic effects as well as gestation duration. No significant differences dependent on birth weight relative to co-twin were found for age at natural menopause in either MZ or dizygotic (DZ) twin pairs, even in pairs whose birth weights differed markedly. There was some indication that twins with premature ovarian failure were heavier at birth than twins with normal or later menopausal age. We conclude that the hypothesis that lower birth weight is associated with earlier menopause is not supported by our data.

Kinematic synergy adaptation to microgravity during forward trunk movement

The aim of the present investigation was to see whether the kinematic synergy responsible for equilibrium control during upper trunk movement was preserved in absence of gravity constraints. In this context, forward trunk movements were studied during both straight-and-level flights (earth-normal gravity condition: normogravity) and periods of weightlessness in parabolic flights (microgravity). Five standing adult subjects had their feet attached to a platform, their eyes were open, and their hands were clasped behind their back. They were instructed to bend the trunk (the head and the trunk together) forward by approximately 35 degrees with respect to the vertical in the sagittal plane as fast as possible in response to a tone, and then to hold the final position for 3 s. The initial and final anteroposterior center of mass (CM) positions (i.e., 200 ms before the onset of the movement and 400 ms after the offset of the movement, respectively), the time course of the anteroposterior CM shift during the movement, and the electromyographic (EMG) pattern of the main muscles involved in the movement were studied under both normo- and microgravity. The kinematic synergy was quantified by performing a principal components analysis on the hip, knee, and ankle angle changes occurring during the movement. The results indicate that 1) the anteroposterior position of the CM remains minimized during performance of forward trunk movement in microgravity, in spite of the absence of equilibrium constraints; 2) the strong joint coupling between hip, knee, and ankle, which characterizes the kinematic synergy in normogravity and which is responsible for the minimization of the CM shift during movement, is preserved in microgravity. It represents an invariant parameter controlled by the CNS. 3) The EMG pattern underlying the kinematic synergy is deeply reorganized. This is in contrast with the invariance of the kinematic synergy. It is concluded that during short-term microgravity episodes, the kinematic synergy that minimizes the anteroposterior CM shift is surprisingly preserved due to fast adaptation of the muscle forces to the new constraint.

Smoking and the genetic contribution to alcohol-dependence risk

Genes influence a person's risk of becoming a smoker as well as the risk of alcohol dependence. Because substantially higher rates of smoking are observed in alcoholics than in control groups, uncovering the mechanisms underlying this association may have important implications for both treatment and prevention. Data analyses from the 1981 Australian twin panel cohort confirm a positive genetic correlation between regular smoking and the risk of alcohol dependence that remains significant, even when sociodemographic and personality variables as well as histories of other psychopathologies are taken into account. Acute or chronic effects of smoking on subjective responses to alcohol may play a role in this association.

Mass spectra of new substituted 2-amino-4H-pyrans: a retro-Diels-Alder reaction pattern

New substituted 2-amino-3-cyano-4H-pyrans have been studied by electron ionization (EI), chemical ionization (CI) and electrospray ionization (ESI) mass spectrometry. The retro-Diels-Alder reaction (RDA) is the main fragmentation pattern observed in the EI spectra forming an unsaturated ketone as the diene fragment. In contrast, a different RDA reaction takes place yielding an unsaturated amide as diene fragment together with the unsaturated ketone in the CI spectra. The MS/MS spectra obtained using an ESI source reveal that the favoured fragmentation by collision induced dissociation (CID) is the elimination of the substituent at the C4 position with formation of a stable pyrilium cation.

Early sexual abuse and lifetime psychopathology: a co-twin-control study

BACKGROUND

This study was designed to determine lifetime prevalence of psychiatric disorders among twins who reported childhood sexual abuse (CSA), and to compare these rates with those among non-abused co-twins. The contribution of familial and individual-specific factors to reported sexual abuse was also examined.

METHOD

Information about lifetime psychopathology and substance use was obtained by structured telephone interviews with 5995 Australian twins. Twins who reported a history of childhood sexual abuse (CSA) were contrasted on lifetime psychopathology with subjects without such a history; in addition, comparisons were made between same-sex twin pairs discordant for CSA.

RESULTS

A history of CSA was reported by 5.9% of the women and 2.5% of the men. In the sample as a whole, those reporting CSA were more likely to receive lifetime diagnoses of major depression, conduct disorder, panic disorder and alcoholism, and were more likely to report suicidal ideation and a history of suicide attempt. Abused women, but not men, were also more likely to report social phobia. When comparisons were restricted to non-abused co-twins, no differences in psychopathology were seen. However, rates of major depression, conduct disorder and suicidal ideation were higher if both co-twins were abused than if the respondent alone reported CSA. Model-fitting indicated that shared environmental factors influenced risk for reported CSA in women, but not in men.

CONCLUSION

The association between CSA and psychopathology arises at least in part through the influence of shared familial factors on both risk of victimization and risk of psychopathology.

Genetic and environmental causes of variation in basal levels of blood cells

The genetic and environmental determinants of variation in blood cell size and number were investigated in 392 pairs of 12-year-old twins. The following blood cell indices were measured: haemoglobin, red blood cell count, haematocrit, mean corpuscular volume, platelet number, total white cell count, level of neutrophils, monocytes, eosinophils, total lymphocytes, CD3+ lymphocytes, CD4+ lymphocytes, CD8+ lymphocytes, CD19+ lymphocytes, CD56+ lymphocytes and CD4+/CD8+ ratio. Genetic factors contributed significantly to all blood cell measures accounting for between 61 and 96% of variance. Heritability estimates did not differ significantly between males and females, although the sample size of the present study was not large enough to exclude the possibility of sex-limited gene expression. Common environmental factors were important in determining red blood cell count and haematocrit, but were not important in determining basal levels of any white blood cell type.

Perceptual variation in grading hand, hip and knee radiographs: observations based on an Australian twin registry study of osteoarthritis

OBJECTIVE

The radiographic diagnosis of osteoarthritis (OA) in the peripheral skeleton is dependent on the skilled examination of several morphological characteristics of the condition as visualised on plain radiographs. However, the process is perceptual and generally enhanced by comparison against photographic standards. This study assessed the intra-rater and inter-rater reliability of radiologists experienced in reporting hand, hip and knee films derived from a community-based sample when using the photographic atlas recently developed by Burnett et al.

METHODS

This study was part of a multifaceted diagnostics protocol, evaluating methodological issues, in the conduct of genetic research in osteoarthritis. From a cohort of 118 twin pairs, registered with the Australian Twins Registry (ATR), standard clinical examinations were performed on 74 complete and 11 incomplete pairs of twins over age 50 years, followed by standard AP hand, AP pelvis and AP standing radiographs of the knees. The pairs were selected both to represent twin pairs who had previously self reported a diagnosis of OA, as well as those who had not. Radiologists read the films blind to the original self reported diagnosis and without reference to their pairing. The films were read by comparison against photographic standards and were scored according to specific features. All films were read independently by two consultant radiologists blind to one another's assessments, and selected films were thereafter assigned for rereading. Inter-rater and intra-rater agreement were different for different features, different anatomic areas, and, for the former, were different for the two radiologists.

RESULTS

Inter-rater agreement was different for different anatomic areas, different radiographic features, and the two radiologists. Intra-rater agreement for the presence or absence of OA was as follows: actual observed agreement = 0.79 to 0.97 and 0.83 to 0.98; adjusted kappa statistic = 0.58 to 0.94 and 0.67 to 0.96; inter-rater agreement was as follows: actual observed agreement = 0. 77 to 0.97; adjusted kappa statistic = 0.54 to 0.94. Agreement was generally high in most of the principal target joints for OA: DIP, PIP, 1st CMC, hip and knee.

CONCLUSIONS

Although assessor agreement was not perfect, it is concluded that for genetic epidemiology purposes, while duplicate assessments may be advantageous, it is possible for radiographs to be examined accurately by a single experienced assessor. However, for less experienced assessors independent examinations should be made by at least two assessors and either a consensus reached on disparate examinations or an algorithm developed to adjudicate any discrepancies.

Production of sulfur flavors by ten strains of Geotrichum candidum

Ten strains of Geotrichum candidum were studied on a liquid cheese model medium for the production of sulfur compounds which contribute to the aroma of cheeses. The volatile components produced by each cultured strain were extracted by dynamic headspace extractions, separated and quantified by gas chromatography (GC), and identified by GC-mass spectrometry. It was shown that four strains of this microorganism produced significant quantities of S-methyl thioacetate, S-methyl thiopropionate, S-methyl thiobutanoate, S-methyl thioisobutanoate, S-methyl thioisovalerate, and S-methyl thiohexanoate. This is the first example of the production of these compounds by a fungus. In addition, dimethyldisulfide, dimethyltrisulfide, dimethylsulfide, and methanethiol, which are more commonly associated with the development of cheese flavor in bacterial cultures, were also produced by G. candidum in various yields, depending on the strain selected. The potential application of these strains in cultured microbial associations to produce modified cheeses with more desirable organoleptic properties is discussed.

Heritability of social cognitive skills in children and adolescents

BACKGROUND

Social cognitive skills are those which enable understanding of social situations; they are relevant to a variety of psychiatric disorders including autism, schizophrenia and externalizing behaviour problems in children.

AIMS

To examine the heritability of social cognitive skills.

METHOD

Using a population-based sample of twins aged 5-17, the genetic and environmental influences on social cognitive skills were examined.

RESULTS

Male scores were higher than female scores (P < 0.001), indicating poorer social cognition among males. A heritability of 0.68 (95% CI 0.43-0.78) was found, with shared environmental influences accounting for only 0.05 of the variance (95% CI 0.00-0.28). This could be removed from the model without worsening the fit. There were no significant differences in genetic effects between the genders, but age-related changes were found, with younger twins showing greater genetic influence on social cognition.

CONCLUSIONS

Social cognition appears to be under considerable genetic influence in the population and shows significant male-female differences. No gender differences in genetic influences on the variance of scores were found, but the effects of age were significant.

Perceptual variation in categorizing individuals according to American College of Rheumatology classification criteria for hand, knee, and hip osteoarthritis (OA): observations based on an Australian Twin Registry study of OA

OBJECTIVE

The American College of Rheumatology (ACR) classification criteria for osteoarthritis (OA) permit the categorization of individuals for hand, knee, and hip OA and are of defined sensitivity and specificity. They depend on both clinical and radiographic aspects of OA. The clinical diagnosis of OA in the peripheral skeleton is dependent on the skilled examination of several clinical features characteristic of the condition, while the interpretation of radiographs is a perceptual skill based on appreciating specific structural features on plain radiographs. We investigated the interrater reliability of the ACR classification criteria for OA when applied in a community based sample.

METHODS

The study was part of a multifaceted diagnostics protocol, evaluating methodologic issues, in the conduct of genetic research in OA. From a cohort of 118 pairs of twins registered with the Australian Twins Registry (ATR), standard clinical examinations of hands, knees, and hips were performed on 74 complete and 11 incomplete pairs of twins over age 50 years. The pairs were selected to represent both twin pairs who had previously self-reported a diagnosis of OA, as well as those who had not. Rheumatologists who performed the assessments were blind to the original self-report. All subjects were examined independently by one of 2 pairs (NB/AK or NB/KM) of consultant rheumatologists, blind to one another's assessments. Each rheumatologist separately assessed the hands, knees, and hips, rating them clinically by ACR criteria for OA. The observations were made without reference to any radiographic or serologic information.

RESULTS

Interrater agreement was different for the 3 different anatomic areas and was different for the 2 pairs of rheumatologists. The actual (observed) interrater agreements based on ACR clinical criteria were as follows: hand OA NB/AK = 0.92, NB/KM = 1.00; knee OA NB/AK = 0.94, NB/KM = 0.92; hip OA NB/AK = 0.98, NB/KM = 0.97. Interrater agreement based on ACR clinical criteria, as assessed by the adjusted kappa statistic, was as follows: hand OA NB/AK = 0.84, NB/KM = 1.00; knee OA NB/AK = 0.87, NB/KM = 0.84; hip OA NB/AK = 0.95, NB/KM = 0.93.

CONCLUSION

Since clinical agreement was extremely high in all 3 anatomic sites, and for both pairs of assessors, we conclude that for genetic epidemiology purposes, subjects can be examined by a single experienced rheumatologist using the ACR classification criteria.

The genetics of smoking persistence in men and women: a multicultural study

Using a correlated liability dimensions model, we examined the extent to which the same genetic and environmental factors influence both initiation of regular cigarette smoking and maintenance of the smoking habit in men and women. We analyzed questionnaire survey data obtained from large samples of male and female like-sexed twins from three countries, Australia (N = 1535 pairs), Sweden (N = 5916 pairs), and Finland (N = 4438 pairs), subdivided into three age bands (18-25, 26-35, and 36-46 years of age). We found that familial influences on risk for persistence in smoking cannot be entirely explained by the same factors responsible for risk of smoking initiation. Total genetic variance for smoking persistence varied little by age band and sex (range, 39-49% in women and 42-45% in men); however, even among twins in the youngest group (18-25 years of age), who on average have the fewest years of cigarette use, less than 40% of the total genetic variance in smoking persistence was accounted for by the same genetic factors that increased risk of smoking initiation, and this percentage decreased to less than 10% in the 36-46 year olds.

An assessment of the genetic relationship between alcohol metabolism and alcoholism risk in Australian twins of European ancestry

The present analyses examined genetic influences on alcohol metabolism and their possible relationship to risk of alcohol dependence. Subjects were 206 Australian twin pairs who participated in an alcohol challenge protocol in 1979-1981, in which they were given a 0.75 g/kg dose of alcohol; blood alcohol concentrations (BACs) measured at five times over a 3-hr period after alcohol ingestion were examined. Structural equation modeling, fitting a combined autoregressive and common factor model, indicated significant heritabilities for both men and women (h2 range = 0.19-0.71), with significant parameter heterogeneity as a function of gender. In 1992-1993, both twins from 159 of the alcohol challenge pairs completed a telephone-administered psychiatric diagnostic interview. Repeated-measures MANOVAs were used to examine whether respondent's or cotwin's DSM-III-R alcohol dependence status, or parental history of alcohol problems, was associated with variation in alcohol metabolism. There was some evidence that individuals at increased genetic risk of alcohol dependence [with either a paternal history of alcohol problems (women) or an MZ male cotwin who reported a history of alcohol dependence by 1992-1993] showed lower initial BACs than other groups. However, this effect was not seen in those who themselves had a history of alcohol dependence by interview follow-up, perhaps because this relationship was already masked by a history of excessive drinking at baseline.

Genetic and social determinants of initiation and age at onset of smoking in Australian twins

Retrospective data on age at onset of smoking, reported by 3810 adult Australian twin pairs, were analyzed to determine the role of genetic and environmental factors in the onset of smoking. Results of nonmetric multidimensional scaling supported a two-process model in which different etiologic factors determined which individuals were at risk of becoming smokers and the age at onset of smoking in those who were at risk. Parametric model-fitting confirmed this difference. For female twins and younger male twins (aged 30 years or less), the onset of smoking was strongly influenced by genetic factors, with shared and nonshared environmental effects having a more modest impact. For older male twins, shared environmental influences on onset of smoking were very important, and the influence of genetic predisposition was slight. The age at which smoking onset occurred, however, was influenced by both genetic and nonshared environmental effects, but not by shared environmental effects, in both sexes and both cohorts.

Arm raising in humans under loaded vs. unloaded and bipedal vs. unipedal conditions

The aim of the present experiment was to study the central organization of equilibrium control during arm raising in the frontal plane. Nine adult subjects (five seniors and four young adults) were asked to raise their right arm to a horizontal position in the frontal plane in two support conditions (bipedal vs. unipedal) and two load conditions (unloaded vs. a 3.5-kg load added on the moving hand). No instructions were given concerning the movement speed. The movements were performed at about half the maximum speed achievable under reaction time conditions. The final lateral center of mass (CM) position 1 s after the movement offset, and the time course of the CM shift during the movement were studied in the four experimental conditions, using a CM compensation index. The electromyographic (EMG) pattern of the main muscles involved in the movement performance and in the postural control were studied in three out of nine subjects during movements performed at two velocities (at the preferred speed and as fast as possible). The results indicate that (1) the CM shift remains minimized in the frontal plane during the time course of the arm movement and during the final stabilization of the arm regardless of the stance and load conditions; (2) the time course of the CM compensation index remains stable during the first 400 ms after the movement onset, decreasing late in the movement and increasing again at the end of the stabilization stage. A modelisation suggests that the time course is the result of the interaction of two controls: a first one, putative feedforward, starting early and decreasing with time and a second one, putative feedback, starting late in the movement and increasing with time; (3) both early and late index values are influenced by the support and load conditions, the highest index values being observed during unipedal stance and load conditions; (4) activation of quadratus lomborum (QL) contralateral to the raising arm is time locked with the deltoidus activation of the raising arm in both fast and slow movements: this contralateral QL activation corresponds to an anticipatory postural adjustment (APA) aimed at minimizing the CM shift.