64 Genetic Basis of Personality Structure
share the same loci. Unlike statistical pleiotropism, biological
pleiotropism unequivocally links actual genes to behavior.
PHENOTYPIC STRUCTURE AND GENETIC
ARCHITECTURE OF PERSONALITY
A critical issue for understanding the etiological structure of
personality and for the use of multivariate genetic analyses to
clarify personality structure is the degree to which the pheno-
typic organization of traits reflects an underlying biological
structure as opposed to the influence of environmental fac-
tors. The evidence indicates that the phenotypic structure of
traits closely resembles the underlying genetic architecture
and to a lesser degree environmental structure. The evidence
also suggests that environmental factors do not appreciably
influence trait covariation. These conclusions are based on
comparisons of the factors extracted from matrices of pheno-
typic, genetic, and environmental correlations computed
among traits comprising a given model or measure.
In one of the earliest studies of this kind, Loehlin (1987)
analyzed the structure of item clusters from the California
Psychological Inventory (CPI; Gough, 1989) in samples of
MZ and DZ twins. Three matrices were derived that repre-
sented the covariance among different traits due to genetic,
shared environmental, and nonshared environmental factors.
When these matrices were examined with factor analysis,
four factors emerged from analyses of genetic covariance that
could be interpreted as representing Neuroticism, Extraver-
sion, Openness, and Conscientiousness (few items related to
the fifth factor, Agreeableness, are included in the CPI; see
McCrae, Costa, & Piedmont, 1993). Analysis of shared envi-
ronmental effects yielded two factors: family problems and
masculinity-femininity. The former is not an aspect of per-
sonality per se, and the latter is probably an artifact of the ex-
clusive use of same-sex twins (Loehlin, 1987). It should be
noted, however, that shared environmental effects make rela-
tively little contribution to the variance of personality traits.
Hence, the important finding is the structure of nonshared en-
vironmental effects. Analysis of the nonshared environmen-
tal covariance matrix yielded three interpretable factors that
resembled Neuroticism, Extraversion, and Conscientious-
ness. Thus, the structure of nonshared environmental influ-
ences largely mirrored genetic influences. This is not an
isolated finding: Livesley et al. (1998) found similar struc-
tures in genetic and nonshared environmental components of
traits related to personality disorder.
Livesley and colleagues (1998) examined the congru-
ence of genetic and phenotypic factor structures and com-
pared phenotypic structure across samples of personality
disordered patients and two samples recruited from the gen-
eral population. The clinical sample consisted of 602 patients
with personality disorder. The general population samples
consisted of 939 volunteer general population participants
and 686 twin pairs. The twin sample allowed the computation
of matrices of genetic and environmental correlations that
could be compared against the phenotypic structures from all
three samples. Personality was assessed with the Dimen-
sional Assessment of Personality Pathology (DAPP; Livesley
& Jackson, in press). This measure assesses 18 traits underly-
ing personality disorder diagnoses that were identified in pre-
vious studies using a combination of clinical judgments,
rational methods, and psychometric procedures (Livesley,
1986; Livesley, Jackson, & Schroeder, 1992).
Phenotypic correlations were computed in all three sam-
ples separately, and genetic and environmental correlations
were computed on the twin sample. The phenotypic, genetic,
and environmental correlation matrices were subjected to
separate principal components analyses with rotation to
oblimin criteria. Phenotypic structure was similar across all
samples. Four factors were extracted from all five matrices
(see Tables 3.1 and 3.2).
The first factor, Emotional Dysregulation, represents un-
stable and reactive affects and interpersonal problems. The
factor resembled neuroticism as measured by the NEO-PI-R
(Costa & McCrae, 1992; Schroeder, Wormworth, & Livesley,
1992) or the Eysenck Personality Questionnaire (EPQ; Jang &
Livesley, 1999) and theDSM-IVdiagnosis of borderline per-
sonality disorder. The second factor, Dissocial Behavior, was
negatively correlated with NEO-PI-R Agreeableness. It de-
scribed antisocial traits and resembled theDSM-IVCluster BTABLE 3.1 Rotated Principal Component Factor Loadings:
DAPP-BQ Dimensions (clinical sample)
Factor
Dimension 1 2 3 4
Submissiveness 0.85
Cognitive Dysregulation 0.64
Identity Problems 0.81
Affective Instability 0.64
Stimulus Seeking 0.76
Compulsivity 0.93
Restricted Expression 0.75
Callousness 0.81
Oppositionality 0.64 −0.47
Intimacy Problems 0.85
Rejection 0.78
Anxiousness 0.86
Conduct Problems 0.74
Suspiciousness 0.50
Social Avoidance 0.76
Narcissism 0.41
Insecure Attachment 0.70 −0.44