24Twin Research and Human Genetics Volume 9 Number 1 pp. 24–29The objective of this study was to estimate the mag-nitude of genetic and environmental influences tovariation in adolescent neuroticism as a function of ageand sex. Neuroticism was assessed using theAmsterdamse Biografische Vragenlijst (ABV): a self-report personality instrument similar in content to theEysenck Personality Questionnaire. Genetic modelingprocedures, including age as modifier, were fitted tothe total sample of 3301 Dutch adolescent twins aged12 to 17 years (mean age 15.5). Significant influencesof additive genetic factors (.59, 95% confidence inter-vals [CI] .54–.63) and unshared environmental factors(.41, 95% CI .37–.45) were found. Our data did notsupport a role of shared environment. Results showedthat different genes may influence variation in neuroti-cism between girls and boys. No interaction wasfound between the variance components and age.Results generally support prior findings in adults andyoung children that neuroticism is influenced princi-pally by additive genetic and unique environmentalfactors. The magnitude of the genetic componentappears higher in the present sample of adolescentsthan in most studies of adults. The present study sug-gests that, in adolescence, different genes areexpressed in boys and girls. The personality trait of neuroticism refers to the rela-tive tendency to experience negative emotions such asfear, sadness, and anger. Over the years, this trait hasbeen variably referred to as neuroticism (Costa &McCrae, 1985; Eysenck & Eysenck, 1975), negativeaffectivity (Rothbart et al., 2000), or emotionality(Buss & Plomin, 1984), among others. The existenceof this dimension has been well supported, and neu-roticism has been studied extensively in part becauseof its links to psychopathology, particularly anxietyand depression (Middeldorp et al., in press).The current diagnostic nomenclature presup-poses the association between personalitydimensions and Axis II but not Axis I disorders(American Psychiatric Association, 1994). Despitethis theoretical conceptualization, however, strongassociations have been found both with personality dis-orders (Jang et al., 1996; Svrakic et al., 1993; Warner etal., 2004) and the ‘major’ Axis I disorders (Caspi et al.,1996; Frick, 2004), shedding doubt about this historicaldistinction. Debate remains, however, as to whether it isbest to conceptualize neuroticism as an important riskfactor for psychopathology or as different points along acommon continuum (Hettema et al., 2004; Nigg &Goldsmith, 1998; Rettew & McKee, 2005). Clarifyingthe relations between personality and psychopathologycould be a major step towards the critical task of pheno-typic refinement on which all of clinical researchdepends (Hudziak, 2002).Research has demonstrated moderate genetic influ-ence of neuroticism in line with most other majorpersonality dimensions (Johnson et al., 2004; Loehlin,1992; Riemann et al., 1997). However, most of thesestudies have been carried out in adults. A Finnishsample of approximately 15,000 twins aged 18 to 59found heritabilities of .17 to .54 for men and .34 to .53for women across different age groups with evidence ofhigher heritabilities in women and decreasing heritabil-ities from late adolescence into early adulthood (Vikenet al., 1994). In perhaps the most comprehensive adultstudy to date involving more than 45,000 individualsin an extended twin design, Lake and coworkers (Lakeet al., 2000) found evidence for the influence of bothadditive (.25 males, .28 females) and nonadditivegenetic factors (.10 males and .13 females) in additionto nonshared environment (.65 males, .58 females).Noteworthy from this study was the finding thatdespite the study’s statistical power to test moreThe Genetic Architecture of Neuroticism in 3301 Dutch Adolescent Twins as a Function of Age and Sex: A Study From the Dutch Twin RegisterDavid C. Rettew,1Jacqueline M. Vink,2Gonneke Willemsen,2Alicia Doyle,1James J. Hudziak,1and Dorret I. Boomsma21 Department of Psychiatry, University of Vermont College of Medicine, Burlington,Vermont, United States of America2Department of Biological Psychology, Vrije University, Amsterdam, the NetherlandsReceived 20 June, 2005; accepted 21 September, 2005.Address for correspondence: Dr David Rettew, Department ofPsychiatry, University of Vermont College of Medicine, 89 BeaumontAvenue, Given Building Room B227, Burlington, Vermont 05405,USA. E-mail: [email protected] models of transmission, this relatively simplemodel, similar to studies using less complicated designs,provided the best fit.While there have been fewer studies of the geneticand environmental influence on neuroticism in childrenand adolescents, mainly additive genetic influences havebeen found in small samples (Graham & Stevenson,1985). Buss and Plomin reported some evidence ofgenetic dominance in an early study of 400 pairs of 5-year-old twins (Buss & Plomin, 1984). The extremelylow correlations reported between dizygotic (DZ) twinscould also have represented a contrast effect (Buss &Plomin, 1984) rather than nonadditive genetic effects.Data in infants and toddlers aged 14 to 36 months fromthe MacArthur Longitudinal Twin Study (Saudino et al.,2001) showed heritability coefficients of .11–.37 withthe remainder of variance primarily due to unsharedenvironmental factors (.47–.89) when using the parent-rated Colorado Childhood Temperament Inventory(Rowe & Plomin, 1977).Among older children, a study of 198 same-sextwin pairs aged 8 to16 found the best fitting model forneurotic symptoms, as measured by the Rutter Aparent scale (Rutter et al., 1970), included additivegenetic (.52) and unshared environmental (.48) factorswith no contribution of shared environment (Thapar& McGuffin, 1996). Gillespie and colleagues (2004)studied a group of 540 Australian adolescent twinpairs age 12 to 16 using the Junior EysenckPersonality Questionnaire (Eysenck & Eysenck,1975). Again, the best fitting models included additivegenetic (.28–.53) and unshared environmental compo-nents (.51–.70). There was some evidence of sharedenvironmental influence for 16-year-old twins,although the authors reported insufficient power totest that hypothesis. In addition, there were also datasupporting higher estimates of additive genetics formales at age 12 in comparison to other ages.In summary, most studies of the genetic architectureof neuroticism have found additive genetic
View Full Document
Unlocking...