Cannabis use, abuse, and dependence in a population-based sample of female twins

OBJECTIVE: The rate of cannabis use by women has been increasing in recent decades. This study examined the etiology of cannabis use and abuse among women and the possible role of genetic risk factors. METHOD: Unselected individual twins (N=1,934) from female-female pairs ascertained through a population-based registry, including both members of 485 monozygotic pairs and of 335 dizygotic pairs, were interviewed by telephone to assess lifetime cannabis use, heavy use, abuse, and dependence as defined by DSM-IV criteria. Biometric model fitting was performed with the Mx computer package. RESULTS: The prevalences of lifetime cannabis use, heavy use, abuse, and dependence were 47.9%, 6.7%, 7.2%, and 2.2%, respectively. Model fitting suggested that twins' resemblance for liability to cannabis use was due to both genetic and familial-environmental factors, while twins' resemblance for heavy cannabis use and abuse and symptoms of dependence resulted solely from genetic factors, with heritabilities ranging from 62% to 79%. The frequency of adolescent social contact between co-twins, which was greater among monozygotic than among dizygotic twins, predicted the twins' resemblance in cannabis use. However, further analyses suggested that the heritability of cannabis use was at most modestly inflated by such social factors. CONCLUSIONS: In women, genetic risk factors have a moderate impact on the probability of ever using cannabis and a strong impact on the liability to heavy use, abuse, and, probably, dependence. By contrast, the family and social environment substantially influences risk of ever using cannabis but plays little role in the probability of developing heavy cannabis use or abuse.     

Hereditary factors in basal cell carcinoma of the skin: a population-based cohort study in twins

The contribution of hereditary factors in basal cell carcinoma of the skin has not been well defined at the population level. We aimed to assess the hereditary component in basal cell carcinoma by comparing its occurrence in monozygotic and dizygotic twin pairs. The Finnish Twin Cohort, comprising 12,941 adult, like-sex twin pairs with established zygosity and resident in Finland in 1975, was linked with the Finnish Cancer Registry. We identified 335 twin pairs in which at least one twin had basal cell carcinoma diagnosed between 1953 and 1996. Standardized incidence ratios, concordances, tetrachoric correlations and pairwise relative risks were computed by standard methods. Components of variance in liability were estimated by structural equation modelling. There was an elevated risk of basal cell carcinoma for the co-twin of a diseased twin, but no difference in risk by zygosity. During the prospective follow-up in 1976-96, the probandwise concordance was 7.7% in monozygotic and 7.0% in dizygotic pairs. Model fitting indicated that genetic factors were not needed to account for the distribution of basal cell carcinoma in twin pairs. These results confirm the major role of environmental factors in the aetiology of basal cell carcinoma.     

Extrathymic and thymic origin of murine IEL: are most IEL in euthymic mice derived from the thymus?

Given the current explosion of knowledge of the genetics and molecular biology of cancer, the possibility of widespread testing for inherited predisposition to cancer has been raised. The main objective of this study was to assess the effect of inherited predisposition on cancer mortality among the National Academy of Sciences-National Research Council Twin Registry. The twins were white male United States veterans of World War II, who were born during the period 1917-1927. The follow-up period was from 1946 to 1990, and some cause of death was determined with the use of death certificates. We compared concordance for death from cancer among 5690 monozygotic twin pairs to that among 7248 dizygotic pairs. A possible effect of inherited predisposition to death from cancer was considered present if concordance for cancer mortality among monozygotic twin pairs was greater than it was among dizygotic twin pairs. Among monozygotic and dizygotic twins, a total of 1918 cancer deaths was observed. Concordance for death from cancer at all sites among monozygotic twins was higher than it was among dizygotic twins (overall rate ratio, 1.4; 95% confidence interval, 1.0-2.0). For each zygosity group, two or fewer pairs were observed to be concordant for death from cancer of a specific site, with the exception of lung cancer.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

The application of structural equation modeling to maternal ratings of twins' behavioral and emotional problems.

The application of structural equation modeling to twin data is used to assess the impact of genetic and environmental factors on children's behavioral and emotional functioning. The models are applied to the maternal ratings of behavior of a subsample of 515 monozygotic and 749 dizygotic juvenile twin pairs, ages 8 through 16 yrs, obtained through mailed questionnaires as part of the Medical College of Virginia Adolescent Behavioral Development Twin Project. The importance of genetic, shared, and specific environmental factors for explaining variation is reported for both externalizing and internalizing behaviors, as well as significant differences in the causes of variation in externalizing behaviors among young boys and girls. The usefulness of applying structural equation models to data on monozygotic and dizygotic twins and the potential implications for addressing clinically relevant questions regarding the causes of psychopathology are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mitogenic activity of neu differentiation factor/heregulin mimics that of epidermal growth factor and insulin-like growth factor-I in human mammary epithelial cells

BACKGROUND: Twin registers provide a valuable source for research into disease causation. The existing population-based registers comprise mostly old twins. In order to be able to study diseases which occur in childhood and youth a new Danish twin register has been established. METHODS: The register is based on the Danish Civil Registration, with information on number of twin births from the Danish Vital Statistics Office as the source of validation. All twins resident in Denmark at 1 March 1991 were sent a one-side questionnaire asking about diabetes, willingness to participate in other research projects and similarity in the twins. RESULTS: The register, comprising 20,888 twin pairs, covers 74.4% of all twin pairs born 1953-1967 (incl.) and 97.4% of those born 1968-1982 (incl.). The response rate to the questionnaire study was 92.3%. The responders represented 19,180 twin pairs distributed as 5304 monozygotic pairs, 6861 same-sex dizygotic pairs, 6244 opposite-sex dizygotic pairs and 771 pairs of unknown zygosity. Of the respondent twins, 96% declared their willingness to participate in additional studies. An analysis of trends in the twinning rates for the years 1968-1982 showed that the rate of monozygotic twinning is increasing and the twinning rate of opposite-sex twin pairs is decreasing. CONCLUSIONS: Earlier estimated trends in twinning rates have been confirmed. Due to the high response rate and opportunities for linkage with other Danish registers, the present material provides a valuable resource for twin studies in diseases and human traits.     

Sources of variability in sex-linked personality attributes: A twin study.

31 pairs of monozygotic (MZ) and 28 pairs of dizygotic (DZ) same-sex, adolescent twins completed Spence and Helmreich's Personal Attributes Inventory, which contains separate scales tapping Masculinity (instrumental traits), Femininity (expressive traits), and bipolar Masculinity–Femininity. Sex-adjusted intraclass correlations were computed for the MZ and DZ twin pairs. Significant twin-pair resemblance was found for Masculinity and Femininity, but not for Masculinity–Femininity. MZ resemblance for Masculinity was greater than DZ resemblance, suggesting a genetic component to masculinity development, but no genetic influence was detected in Femininity. All 3 traits showed substantial within-families variability, and it is concluded that future research should give equal attention to nonshared developmental influences that operate to make siblings dissimilar and to shared developmental influences. (10 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Is caffeine addictive? The most widely used psychoactive substance in the world affects same parts of the brain as cocaine

Caffeine is the most widely used psychoactive substance in the world. In Western society, at least 80 per cent of the adult population consumes caffeine in amounts large enough to have an effect on the brain. Is this due to caffeine dependence? The article reviews the abuse potential of caffeine in relation to its mechanisms of action. Caffeine affects the same parts of the brain as cocaine, but in completely different ways. There is evidence for caffeine withdrawal symptoms, and caffeine does act as a weak reinforcer, but neither effect is as pronounced as those associated with cocaine. Nor does caffeine use appear to pose any threat to the individual or to society. There is thus no need to add diagnosis "caffeine dependence" to the psychiatric manuals.     

Genetic architecture of learning and delayed recall: A twin study of episodic memory.

Objective: Although episodic memory is often conceptualized as consisting of multiple component processes, there is a lack of understanding as to whether these processes are influenced by the same or different genetic determinants. The aim of the present study was to utilize multivariate twin analyses to elucidate the degree to which learning and delayed recall, two critical measures of episodic memory performance, have common or different genetic and environmental influences. Method: Participants from the Vietnam Era Twin Study of Aging (314 monozygotic twin pairs, 259 dizygotic twin pairs, and 47 unpaired twins) were assessed using the second edition of the California Verbal Learning Test. Mean age at the time of the evaluation was 55.4 years (SD = 2.5). Results: Model fitting revealed the presence of a higher-order latent factor influencing learning, short- and long-delay free recall, with a heritability of .36. The best-fitting model also indicated specific genetic influences on learning, which accounted for 10% of the overall variance. Given that learning involves the acquisition and retrieval of information, whereas delayed recall involves only retrieval, we conclude that these specific effects are likely to reflect genes that are specific to acquisition processes. Conclusion: These results demonstrate that even in nonclinical populations, it is possible to differentiate component processes in episodic memory. These different genetic influences may have implications for gene association studies, as well as other genetic studies of cognitive aging and disorders of episodic memory such as Alzheimer's disease or mild cognitive impairment. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Sex differences and nonadditivity in heritability of the Multidimensional Personality Questionnaire Scales.

A sex-limitation model was applied to the Multidimensional Personality Questionnaire (MPQ) data from the Minnesota Twin Family Registry. The sample included 626 monozygotic (MZ) twin pairs, 517 same-sex dizygotic (DZ) twin pairs, and 114 opposite-sex DZ twin pairs ranging in age from 27 to 64 years (mean age?=?37.8). In addition, whenever possible, family members of the twins were also assessed: 1,690 spouses, 495 parents, 322 siblings, and 535 offspring. The goals of the present investigation were to analyze the covariance matrices to determine whether (a) there was evidence for sex limitation of heritability of the MPQ scales and (b) there was evidence for nonadditive genetic influences on these scales. Significant sex differences in heritability were found for 3 of the scales: Alienation, Control, and Absorption. In addition, evidence for dominance was found for all scales except Traditionalism and Absorption. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Parkinson disease in twins: an etiologic study

CONTEXT: The cause of Parkinson disease (PD) is unknown. Genetic linkages have been identified in families with PD, but whether most PD is inherited has not been determined. OBJECTIVE: To assess genetic inheritance of PD by studying monozygotic (MZ) and dizygotic (DZ) twin pairs. DESIGN: Twin study comparing concordance rates of PD in MZ and DZ twin pairs. SETTING AND PARTICIPANTS: A total of 19842 white male twins enrolled in the National Academy of Sciences/National Research Council World War II Veteran Twins Registry were screened for PD and standard diagnostic criteria for PD were applied. Zygosity was determined by polymerase chain reaction or questionnaire. MAIN OUTCOME MEASURE: Parkinson disease concordance in twin pairs, stratified by zygosity and age at diagnosis. RESULTS: Of 268 twins with suspected parkinsonism and 250 presumed unaffected twin brothers, 193 twins with PD were identified (concordance-adjusted prevalence, 8.67/1000). In 71 MZ and 90 DZ pairs with complete diagnoses, pairwise concordance was similar (0.129 overall, 0.155 MZ, 0.111 DZ; relative risk, 1.39; 95% confidence interval, 0.63-3.1). In 16 pairs with diagnosis at or before age 50 years in at least 1 twin, MZ concordance was 1.0 (4 pairs), and DZ was 0.167 (relative risk, 6.0; 95% confidence interval, 1.69-21.26). CONCLUSIONS: The similarity in concordance overall indicates that genetic factors do not play a major role in causing typical PD. No genetic component is evident when the disease begins after age 50 years. However, genetic factors appear to be important when disease begins at or before age 50 years.     

A comparison of digital luminescence mammography and conventional film - screen system: preliminary results of clinical evaluation

The heritability of total plasma testosterone levels, determined from blood samples, was examined in 160 adolescent twin pairs and their parents. Subjects were tested as part of a larger study of cardiovascular risk factors, conducted in Amsterdam. Each subject provided a sample of blood which was assayed to measure testosterone concentrations. Correlations of testosterone in monozygotic twins were higher than in dizygotic twins. No resemblance was found between testosterone values in fathers and those in their children and a moderate correlation was seen between mothers and their daughters. The lack of resemblance between family members of opposite sex suggests that different genetic factors influence plasma testosterone concentrations in men and women. In adolescent men, approximately 60% of the variance in testosterone levels is heritable. The lack of father-son resemblance suggests that different genetic factors may be expressed in adolescence and adulthood. In women, 40% of the variance in testosterone levels is heritable, both in adolescence and in adulthood.     

Genetic influences on memory performance in adulthood: Comparison of Minnesota and Swedish twin data.

Results from 2 twin studies of aging differ concerning the heritability of memory performance in adulthood. Heritability estimates from the Minnesota Twin Study of Adult Development and Aging (MTSADA; D. Finkel & M. McGue, see record 1994-17107-001) are larger than estimates from the Swedish data (N. L. Pedersen, R. Plomin, J. R. Nesselroade, & G. E. McClearn; see record 1993-20499-001). Memory data were available from MTSADA on a sample of 112 monozygotic (MZ) twin pairs and 111 dizygotic (DZ) twin pairs ages 27 to 88 years and from the Swedish study on a sample of 86 MZ and 110 DZ twin pairs who were reared together and were ages 27 to 85 years. Univariate and multivariate behavior genetic analyses were conducted to determine the significance and source of differences in heritability across studies. No significant age differences were found in either study. Study differences were found at the level of specific memory measures, but not at the level of a general memory factor. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Manual performance and laterality in twins of known chorion type

Manual performance, direction, and degree of laterality were tested in monozygotic (MZ) twins (8-12 years old) of known chorion type and dizygotic (DZ) twins. Three manual tasks rarely employed in twin studies were used; dot-filling, tapping, and peg-moving tasks. No chorion effect was observed: the monochorionic and dichorionic MZs differed neither for frequency of discordant pairs nor for handedness, laterality measurements, and manual performance. The pooled MZs and DZs were then compared in a classic twin design. The within-pair resemblance was not higher in MZs than in DZs for variables measuring level of manual performance. For laterality scores intraclass correlations were close to zero in MZ and DZ twin groups.     

The structure of self-concept in female preadolescent twins: a behavioral genetic approach

Two hundred and forty-three female monozygotic (MZ) and 164 female dizygotic (DZ) twin pairs, aged 11 and 12 years, who participated in the ongoing Minnesota Twin Family Study, completed six specific scales of the Piers-Harris Children's Self-Concept Scale (P-H). Model-fitting analyses yielded three major conclusions. First, approximately 30% of the variance in specific self-concepts in female preadolescents was due to genetic factors, with the remaining variance being accounted for primarily by nonshared environmental factors and measurement error. Second, the underlying common genetic, shared environmental, and nonshared environmental factors influenced specific facets of self-concept directly and independently, rather than through an intervening phenotypic general self-concept. Finally, whereas genetic, shared environmental, and nonshared environmental factors were necessary to explain the commonality among the specific self-concept scales, only genetic and nonshared environmental factors were sufficient to explain the specificity of those scales.     

Age and the self-perception of ability: A twin study analysis.

2,974 adults, including 678 monozygotic and 547 dizygotic twin pairs (aged 27–86 yrs), self-rated ability on 6 factors: Interpersonal Competence, Workplace Skills, Trade Skills, Intellectual and Cultural, Domestic Skills, and Athletic Competition. Age accounted for no more than 2% of the variance on any factor, and, although there were significant gender effects, no significant Age?×?Gender interactions were observed. Twin similarity did not vary significantly with age, and biometrical variance component estimates were statistically homogeneous across age, with talent factor variance being apportioned approximately equally to genetic and nonshared environmental factors. Consistent failure to find age effects as well as consistent observation of significant heritability support the conclusion that self-concept crystallizes early in adulthood and reflects genetically influenced psychological characteristics. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Familial resemblance in infant mental development.

Compared the scores on a scale of mental development (N. Bayley) of 151 sets of 8-mo-old twins and 2,481 other sibling pairs in the Collaborative Perinatal Project. Intraclass correlation coefficients between scores of twins were high (.84, monozygotic; .55, dizygotic), suggesting a substantial genetic influence; however, the average correlation between scores of other siblings was only .22. The discrepancy between the values for dizygotic twins and other sibling pairs may have resulted from the twins' greater environmental similarity. The high heritability estimate derived from the difference between monozygotic and dizygotic correlations was due to the higher concordance for severe retardation in monozygotic pairs. It is noted that since infant twins are a unique sample in terms of retardation frequency as well as birth weight and gestational age, it may be inappropriate to generalize infant twin study results to singleton populations. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Nutrient intake and food group consumption of 10-year-olds by sugar intake level: the Bogalusa Heart Study

We studied the occurrence of nocturnal enuresis (bedwetting) after the age of 4 years, using a questionnaire in a well-defined population, the Finnish Twin Cohort, which consists of 11,220 subjects aged 33-60 years, including 1298 monozygotic and 2419 dizygotic twin pairs. Structural equation modeling techniques were used to estimate variance components to compare different genetic models. Females reported enuresis in childhood "often" in 3.4% (males in 4.0%) and "sometimes" in 5.7% (8.0%). As adults, females had experienced enuresis "weekly" in 0.3% (males in 0.2%) and "monthly" in 0.07% (0.1%). Those who had experienced enuresis in childhood had had "at least sometimes" enuresis as adults in 5.4% of males and in 5.5% of females. Among those who reported they never had experienced enuresis as adults, 70.8% of males and in 77.9% of females had never experienced enuresis in childhood. For enuresis in childhood, the probandwise concordance rate was 0.43 for monozygotic and 0.19 for dizygotic pairs, and in adults 0.25 and 0, respectively. The proportion of total phenotypic variance attributed to genetic influences (due to dominance) was 67% in males (95% confidence interval 57-76%) and 70% in females (61-78%) in childhood enuresis. In conclusion, nocturnal enuresis is common in childhood and rare in adulthood. Our results confirm the central role of genetic liability in enuresis.     

Zygosity and intrauterine growth of twins

Six hundred seventy-eight sonar measurements of the fetal biparietal diameter (BPD) were used to assess the intrauterine growth of 182 twins between 18 and 40 weeks' gestation. These values, as well as the weight and body length at birth, were related to the zygosity, which was determined by sex of the infants, histologic examination of placenta, or blood grouping. The mean BPD of twin 1 was larger than that of twin 2 in both monozygotic and dizygotic pairs throughout the study period (P less than .001). The size of BPD of the dizygotic infants exceeded that of the monozygotic among both twin 1 (P less than .001) and twin 2 (P less than .001). The absolute intrapair differences of birth length and weight were larger among dizygotic than among monozygotic twins. These findings suggest that in late pregnancy a substantial one-way intertwin transfusion among monochorial twins does not occur frequently enough to mask the inherent genetically determined similarity between the twins. The appearance already in the second trimester of the difference in the longitudinally monitored BPD between monozygotic and dizygotic twins suggests that the discrepancy is determined early in gestation.     

Genetic association between atopy and behavioral symptoms in middle childhood

The relationship of atopic and behavioral symptoms in a community sample of 66 monozygotic and 141 dizygotic twin pairs, ages 4-11 years, was investigated via mother report questionnaires. Within-person correlation between atopic symptoms and Child Behavior Checklist internalizing symptoms (CBCL-INT) was .21 (p < .001) for the total sample. Cross-correlations between atopy and CBCL-INT were .26 for monozygotic and .04 for dizygotic twins. A common and specific factor model applied to the data revealed that the cross-correlation between atopy and CBCL-INT was mainly due to genetic influences (77% of the covariance). This study supports the hypothesis that there is a shared genetic risk for atopy and internalizing symptoms.