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Impact of Normal Sexual Dimorphisms on Sex Differences in Structural Brain Abnormalities in Schizophrenia Assessed by Magnetic Resonance Imaging
Jill M. Goldstein, PhD;
Larry J. Seidman, PhD;
Liam M. O'Brien, MS;
Nicholas J. Horton, ScD;
David N. Kennedy, PhD;
Nikos Makris, MD, PhD;
Verne S. Caviness, Jr, MD, DPhil;
Stephen V. Faraone, PhD;
Ming T. Tsuang, MD, PhD
Arch Gen Psychiatry. 2002;59:154-164.
ABSTRACT
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Background Previous studies suggest that the impact of early insults predisposing
to schizophrenia may have differential consequences by sex. We hypothesized
that brain regions found to be structurally different in normal men and women
(sexual dimorphisms) and abnormal in schizophrenia would show significant
sex differences in brain abnormalities, particularly in the cortex, in schizophrenia.
Methods Forty outpatients diagnosed as having schizophrenia by DSM-III-R were systematically sampled to be comparable within sex with
48 normal comparison subjects on the basis of age, ethnicity, parental socioeconomic
status, and handedness. A comprehensive assessment of the entire brain was
based on T1-weighted 3-dimensional images acquired from a 1.5-T magnet. Multivariate
general linear models for correlated data were used to test for sex-specific
effects regarding 22 hypothesized cortical, subcortical, and cerebrospinal
fluid brain volumes, adjusted for age and total cerebrum size. Sex x
group interactions were also tested on asymmetries of the planum temporale,
Heschl's gyrus, and superior temporal gyrus, additionally controlled for handedness.
Results Normal patterns of sexual dimorphisms were disrupted in schizophrenia.
Sex-specific effects were primarily evident in the cortex, particularly in
the frontomedial cortex, basal forebrain, cingulate and paracingulate gyri,
posterior supramarginal gyrus, and planum temporale. Normal asymmetry of the
planum was also disrupted differentially in men and women with schizophrenia.
There were no significant differential sex effects in subcortical gray matter
regions or cerebrospinal fluid.
Conclusion Factors that produce normal sexual dimorphisms may be associated with
modulating insults producing schizophrenia, particularly in the cortex.
INTRODUCTION
NUMEROUS STUDIES have demonstrated sex differences in the phenomenology
and genetic transmission of schizophrenia (see review by Goldstein and Lewine1). Although one's sex modifies the phenotypic expression
of schizophrenia, there is some debate about whether these differences have
etiologic implications.1 Recent research has
begun to examine whether sex differences in brain abnormalities in schizophrenia
contribute to explaining the heterogeneous phenotypic illness expression.
This is a reasonable expectation, since other neurodevelopmental disorders
have shown sex-mediated neurobehavioral and neuroanatomic consequences.2 One question of interest has been whether sex differences
in schizophrenia are similar, but exaggerated, normal sex differences in the
brain, or whether one's sex is a risk factor for the illness per se, since
there is a slightly but significantly higher incidence among men.3-4
Relatively few previous studies have been designed to test for sex differences
in structural brain abnormalities in schizophrenia, and there was a tendency
among them to find greater abnormalities among the men.5
Magnetic resonance (MR) imaging and postmortem studies showed that men had
larger lateral and third ventricles6-7
and anterior temporal horn,8 and smaller medial
temporal volume, eg, hippocampus and amygdala,8-9
Heschl's gyrus,10-11 superior
temporal gyrus,9-10 and overall
frontal12 and temporal13
lobe volumes (findings not wholly consistent).14-15
In addition, more left-lateralized abnormalities among men were reported,7-8,13 such as smaller volumes
of the left planum temporale (PT),16-19
left Heschl's gyrus,16 left superior temporal
gyrus,20 and left hippocampus.8, 21
Other abnormalities more likely to be found in men with schizophrenia, eg,
greater sulcal volume22 and smaller thalamic
size,6 suggested somewhat more pervasive brain
damage in men than women.5
However, recent work with the use of more refined measures of the cortex
have reported smaller volumes among women as well as men, depending on the
cortical region assessed. Some have reported smaller volumes of heteromodal
association areas among women with schizophrenia (eg, dorsolateral prefrontal
cortex and superior temporal gyrus23 and orbital
prefrontal cortex24). However, others found
smaller volumes of superior temporal gyrus in men10, 20, 25
and similar abnormalities in men and women in dorsolateral prefrontal cortex.24 A recent study,24
which involved a large sample and refined segmentation of prefrontal regions,
demonstrated different differences between men and women with schizophrenia
compared with their normal counterparts, depending on the particular prefrontal
region assessed. The inconsistencies across studies may be, in part, due to
methodologic and sample size differences and to a relative dearth of conceptual
models tested in studies of sex differences.
In this study, we propose a heuristic framework for examining sex effects
in schizophrenia that we will begin to test indirectly. Our initial premise,
based on numerous studies, is that the risk for schizophrenia is initiated
during prenatal (especially second and third trimesters) and perinatal development.26-31
Furthermore, animal studies have demonstrated that the critical early period
of the sexual differentiation of the brain, so-called organizational effects
of gonadal hormones, also occurs in second- and third-trimester and early
postnatal development (for review see Kawata32).
We thus hypothesized that the organizational effects of gonadal hormones,
occurring during the same developmental period as risk factors for schizophrenia,
would modify brain abnormalities differentially in males and females who later
developed schizophrenia. We hypothesized that the cortex would be more vulnerable
to sex-specific brain abnormalities, since animal studies have shown that
the cortex has a high density of gonadal hormone receptors only during these
early critical periods of development, which then primarily recede postnatally.33-35 This is an extension
of previous findings by our group,36 in which
sex differences in brain volumes in normal adults (subsequently referred to
as normal sexual dimorphisms) were more often found in homologous regions
in humans that were implicated in animal studies to have a high density of
gonadal hormone receptors in these early periods of development compared with
regions that had not been so identified. The largest sex differences were
in the cortex.36
Those findings on normal sexual dimorphisms were consistent with a number
of previous imaging and postmortem studies of normal subjects. Compared with
men, relative to cerebrum size, women have been found to have relatively larger
volumes of Broca's area,36-37
superior temporal cortex,36-39
hippocampus,36, 40-42
caudate,40, 42 thalamic nuclei,42 anterior cingulate gyrus,36, 43
dorsolateral36, 38 and orbital
prefrontal36 cortices, inferior parietal lobe,36, 44 and overall cortical gray matter
volume.36, 45 Cell packing density,
or number of neurons per unit volume, in the PT was also greater in women
than men.46 Compared with women, men have been
found to have larger volumes, relative to cerebrum size, in the amgydala,36, 41 hypothalamus,36, 47-48
paracingulate gyrus,36, 43 medial
prefrontal cortex,36 and CSF (lateral ventricles49-50 or sulcal volume45).
Abnormalities in these brain regions have been implicated in schizophrenia,
thus suggesting that normally sexually dimorphic brain regions may be particularly
affected in schizophrenia. Thus, we hypothesize that factors affecting normal
sexual dimorphisms have implications for understanding brain abnormalities
in schizophrenia.
This study will analyze regions that have been found in animal studies
to have a high density of sex steroid receptors prenatally and perinatally33-34,51-52 and
found to be abnormal in schizophrenia, which include middle frontal gyrus;
frontomedial and fronto-orbital cortices; basal forebrain; anterior, posterior,
and paracingulate gyri; insula; parahippocampal gyrus; posterior parietal
cortex (angular and supramarginal gyri); primary auditory cortex (Heschl's
gyrus); and subcortical regions: amygdala, hippocampus, dorsal medial thalamic
nuclei, and the caudate, putamen, and globus pallidum. We hypothesized that
significant sex-specific effects in schizophrenia (ie, disturbed normal sexual
dimorphisms) would be more likely in cortical than subcortical regions. In
exploratory analyses, we were also interested in testing whether sex differences
in normal asymmetries, reported in Heschl's gyrus, superior temporal gyrus,
PT, and Broca's area,10, 53-55
would be disturbed in schizophrenia.
SUBJECTS AND METHODS
SUBJECTS
Cases were recruited from 3 public psychiatric hospitals in the Boston,
Mass, area serving primarily psychotic patients.56-58
The sample included subjects described previously for the cortex59
and for subcortical regions and cerebrospinal fluid (CSF).60
Inclusion criteria for recruitment consisted of subjects between the ages
of 23 and 68 years at MR imaging, who had at least an eighth-grade education,
English as their first language, and an estimated IQ of 70 or more. Exclusion
criteria for subjects were substance abuse within the past 6 months; history
of head injury with documented cognitive sequelae or loss of consciousness
for longer than 5 minutes; neurologic disease or damage; mental retardation;
and medical illnesses that significantly impair neurocognitive function. (Only
3 subjects had past substance dependence, and analyses were run with and without
them.) Written informed consent was obtained after a complete description
of the study was given to the subjects.
Normal comparison subjects were recruited through advertisements in
the catchment areas and notices posted on bulletin boards at the hospitals
from which the patients were ascertained. They were selected to be proportionately
comparable to patients on age, sex, ethnicity, parental socioeconomic status,
and handedness. They were screened for current psychopathology by means of
a short form of the Minnesota Multiphasic Personality Inventory61
and family history of psychoses or psychiatric hospitalizations. We excluded
potential controls if they had current psychopathology or lifetime history
of any psychosis, family history of psychosis, or psychiatric hospitalization,
or if any Minnesota Multiphasic Personality Inventory clinical or validity
scale score, except Masculinity-Femininity, was above 70.
The case sample consisted of probands with a DSM-III-R diagnosis of schizophrenia (n = 40), based on the Schedule for Affective
Disorders and Schizophrenia62 and a systematic
review of the medical record. Interviews were obtained by masters-level interviewers
with extensive diagnostic interviewing experience. Senior investigators (J.M.G.
and L.J.S.) reviewed the interview and medical record to determine the consensus,
best-estimate, lifetime diagnosis. Blindness of assessments was maintained
among MR imaging data and psychiatric status and subject's sex.
Cases had an average age at MR imaging of 45 years and parental education
of 12 years (Table 1). They were
primarily Caucasian, from middle to lower-middle socioeconomic backgrounds,
with an average of some college education. Measures of premorbid and current
IQ were in the average range. There were no significant differences in age,
parental education, ethnicity, parental socioeconomic status, single word
reading ability, or handedness by sex. There was a small, but significant,
sex difference in IQ and patient education, ie, lower among men, which is
typical of schizophrenia.
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Table 1. Sociodemographic and Clinical Characteristics of the Men and
Women*
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Patients primarily had undifferentiated or paranoid subtypes (Table 1). All cases were clinically stable,
and only 5 of 40 were ascertained as inpatients. They were rated as having
mild to moderate negative and positive symptoms, on the basis of the Schedules
for Positive and Negative Symptoms63-64
(Table 1). The patients were a
chronically disabled group, as seen in Table 1, and their conditions were maintained with an average chlorpromazine-equivalent
neuroleptic daily dose of 600 to 700 mg, not significantly different by sex.
MR IMAGING PARAMETERS AND SEGMENTATION PROCEDURES
The MR images were acquired at the NMR Center of the Massachusetts General
Hospital, Boston, with a 1.5-T scanner (Signa; General Electric Co, Milwaukee,
Wis). Contiguous 3.1-mm coronal spoiled gradient echo images of the entire
brain were obtained by means of the following parameters: repetition time,
40 milliseconds; echo time, 8 milliseconds; flip angle, 50°; field of
view, 30 cm; matrix, 256 x 256; and averages, 1. The MR images were
processed and analyzed at the Massachusetts General Hospital Center for Morphometric
Analysis. Images were positionally normalized by imposing a standard 3-dimensional
coordinate system on each 3-dimensional MR image with the use of the midpoints
of the decussations of the anterior and posterior commissures, and the midsagittal
plane at the level of the posterior commissure, as points of reference for
rotation and (nondeformation) transformation.40, 67
Scans were then resliced into the normalized 3.1-mm coronal scans. Positional
normalization overcomes potential problems caused by variation in head position
across subjects during scanning.
Each slice of the T1-weighted, positionally normalized 3-dimensional
coronal scans was segmented into gray and white matter and ventricular structures
by means of a semiautomated intensity contour mapping algorithm and signal
intensity histogram distributions. This technique, described in previous reports40, 59, 67-69
and illustrated in Figure 1, yields
separate compartments of neocortex, subcortical gray nuclei, white matter,
and ventricular system subdivisions, generally corresponding to the natural
tissue boundaries distinguished by signal intensities in the T1-weighted images.
The neocortex, defined by the gray-white matter segmentation procedure, was
subdivided into bilateral parcellation units, based on the system described
by Caviness et al67 and applied by Goldstein
et al59 to patients with schizophrenia. This
is a comprehensive system for neocortical subdivision, designed to approximate
architectonic and functional subdivisions, and based on specific topographic
anatomic landmarks present in virtually all brains (see detailed anatomic
definitions67-68 and Figure 1). The diencephalon was partitioned
into dorsal thalamus and epithalamus above and hypothalamus and subthalamus
below by a transaxial plane positioned on the z-axis at the level of the anterior
commissure–posterior commissure line, which approximates the diencephalic
fissure.70 The dorsal thalamus was further
subdivided along the y-axis into anterior, medial, lateral-anterior, lateral-posterior,
and posterior topographic parcellation units, described by Makris et al70 and applied to schizophrenia by Seidman et al.60 Volumes, measured in cubic centimeters, were calculated
for each brain region by multiplying the slice thickness by the region's area
measurements on each slice, and summing all slices on which the region appeared.
Very good interrater and intrarater reliability of the cortical, subcortical,
and CSF regions has been established in previous studies.59, 67, 69
Furthermore, the concurrent, discriminant, and predictive validity of these
techniques has been demonstrated in numerous studies of normal subjects and
various patient populations.40, 59, 69, 71-73
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Figure 1. Segmentation and parcellation.
Cortical abbreviations: AG indicates angular gyrus; BF, basal forebrain; CGa,
cingulate gyrus, anterior division; CGp, cingulate gyrus, posterior division;
CN, cuneus; CO, central operculum; F1, superior frontal gyrus; F2, middle
frontal gyrus; F3t, inferior frontal gyrus, pars triangularis; F3o, inferior
frontal gyrus, pars opercularis; FMC, frontomedial cortex; FOC, fronto-orbital
cortex; FP, frontal pole; H1, Heschl's gyrus; INS, insula; JPL, juxtaparacentral
lobule; OLi, occiptal lateral gyri, inferior division; OLs, occipital lateral
gyri, superior division; OP, occipital pole; PAC, paracingulate cortex; PCN,
precuneus; PHa, parahippocampal gyrus, anterior division; POG, postcentral
gyrus; PP, planum polare; PRG, precentral gyrus; PT, planum temporale; SC,
subcallosal cortex; SGa, supramarginal gyrus, anterior division; SGp, supramarginal
gyrus, posterior division; SMC, supplementary motor cortex; SPL, superior
parietal lobule; T1, superior temporal gyrus; T1a, superior temporal gyrus,
anterior division; T1p, superior temporal gyrus, posterior division; T2a,
middle temporal gyrus, anterior division; T2p, middle temporal gyrus, posterior
division; T3a, inferior temporal gyrus, anterior division; T3p, inferior temporal
gyrus, posterior division; TFa, temporal fusiform gyrus, anterior division;
TFp, temporal fusiform gyrus, posterior division; T02, middle temporal gyrus,
temporo-occipital division; T03, inferior temporal gyrus, temporo-occipital
division; and TP, temporal pole. Subcortical abbreviations: A Thal indicates
anterior thalamic division; AL Thal, anterior lateral thalamic division; M
Thal, medial dorsal thalamic division; PL Thal, posterior lateral thalamic
division; P Thal, posterior thalamic division; and VentDC, ventral diencephalon.
Regarding correction for head tilt, the interpolation used in the positional
normalization step is trilinear. Reformatting may cause "interpolation error,"
ie, attenuation of high spatial frequency in the processed image data. However,
measurement of brain regions requires "secondary" segmentation definitions
that require the use of anatomically specified "cutting lines." To standardize
these anatomic definitions, which are dependent on the orientation of the
brain within the data matrix, we force the image data into a common orientation.
The "loss" of precision due to interpolation error is less than the "gain"
of reliability and reduction of systematic volumetric variability caused by
the use of a standard orientation.
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STATISTICAL ANALYSES
Significant interaction effects of sex and group (ie, patients with
schizophrenia vs normal control subjects) were hypothesized for cortical regions:
middle, medial, and orbital prefrontal cortices; basal forebrain; cingulate
and paracingulate gyri; parahippocampal gyrus; posterior parietal cortex (operationalized
as supramarginal and angular gyri); and Heschl's gyrus. Subcortical and CSF
regions included the hippocampus, amygdala, medial dorsal thalamic nuclei,
and basal ganglia. Lateral and third ventricles were also included in the
analyses, since earlier studies found significant sex differences (see introduction).
We tested the hypothesis that significant sex x group interactions would
be more likely in hypothesized cortical than subcortical or CSF regions. To
conduct this 2-group comparison, a normalized summary measure, the absolute
value of the t statistic, was calculated for sex
x group interactions for each brain area. This estimated the mean magnitude
of a different difference in volumes for female and male cases compared with
their normal counterparts. A permutation test74
was conducted to examine whether the distribution of these 22 standardized
scores significantly differed on the basis of the dichotomous grouping. Specifically,
a t statistic was calculated by means of the observed
22 scores; the magnitude of this test was compared with 20 000 iterations
in which the brain regions were randomly regrouped. Under the null hypothesis
that there was no difference in the significance of sex x group effects
for the cortical vs subcortical distinction, the observed t statistic was not expected to be extreme when compared with the permutation
distribution. We have applied this method successfully to our normal control
sample.36
Multivariate general linear models for correlated data were also used
for cortical and subcortical or CSF regions separately; controlled for age,
given a large age range; and total cerebral volume, given that men have larger
cerebrums than women. The model was appropriate because tests of normality
showed that the brain volumes were, in general, normally distributed. Significance
levels were based on P values of .05 or less. Effect
sizes,75 based on volume differences relative
to cerebrum size, were estimated as follows: adjusted mean female brain volume
minus adjusted mean male brain volume, divided by the pooled SD of male and
female volumes. Effect sizes are unaffected by sample size and thus can be
compared across studies.
In a separate general linear model for analyses of asymmetries, we tested
sex x group interaction effects on asymmetries of Heschl's gyrus, superior
temporal gyrus, PT, and Broca's area, additionally controlled for handedness
and handedness x group interaction effects. The subject had to score
5 of 6 items on the Annett scale, including writing hand, to be considered
right- or left-handed. Asymmetries were measured76
with the use of 2 times left hemisphere volume minus right hemisphere volume
divided by left plus right hemisphere volumes. Thus, a positive value represented
greater left-sided volume; a negative value, greater right-sided volume; and
around 0, symmetry.
RESULTS
Consistent with numerous studies, the total cerebrum was larger in men
than women within both groups, and not significantly different between the
sexes across groups. In contrast, the total cortex, relative to cerebrum size,
was larger in women than men, again regardless of group status (Table 2). Overall cortical gray matter in female and male cases
compared with their normal counterparts was smaller, with women showing a
larger, but nonsignificant, effect size than the men (Table 3, effect sizes).
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Table 2. Brain Volumes, Adjusted for Cerebrum Size, in Men and Women
With Schizophrenia and Normal Control Subjects: Sex x Group Interactions
and Effect Sizes*
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Table 3. Brain Volumes, Unadjusted for Cerebrum Size, in Men and Women
With Schizophrenia and Normal Control Subjects: Sex x Group Interactions
and Effect Sizes*
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We tested the hypothesis that significant sex x group interactions
would be more likely in hypothesized cortical than subcortical or CSF regions.
The permutation test74 (see "Subjects and Methods"
section for explanation) showed that only 86 of 20 000 iterations yielded
a more extreme value than the observed data (P =
.004; SE [P] = .0005; 95% confidence interval, .003-.005).
Thus, there was a significantly greater likelihood of the presence of a sex
x group interaction effect for the cortical regions than the subcortical
or CSF regions, which was consistent with the significant overall F test resulting
from the general linear model for correlated data for the cortex only (sex
x area x group interaction: F12,87 = 2.59, P = .005; see Table 3).
As seen in Table 2 and Table 3, in which the order of the brain
regions was based on the size (ie, largest effects first) of the significance
of the sex x group interaction effects, male patients compared with
male comparison subjects had smaller volumes of frontomedial and middle frontal
cortices, paracingulate gyrus, insula, Heschl's gyrus, and Broca's area, and
larger volumes of the posterior cingulate gyrus and basal forebrain than in
female patients compared with their normal counterparts. Female cases compared
with female normal subjects had smaller volumes of fronto-orbital cortex,
basal forebrain, anterior cingulate gyrus, and posterior supramarginal gyrus,
and larger volumes of the angular gyrus and right PT than in men compared
with their normal counterparts. The univariate t
tests for sex-specific effects were significant (at P .05)
for the cingulate and paracingulate gyri, frontomedial cortex, basal forebrain,
posterior supramarginal gyrus, and PT (Table 2). There were no significant sex differences in volumetric
abnormalities in the hypothesized subcortical or CSF regions. Sex effects
for cortical and subcortical regions are illustrated in Figure 2.
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Figure 2. Sex x group interaction
effects in subjects with schizophrenia vs normal control subjects: cortical
normal sexual dimorphisms disrupted. Sample sizes were as follows: normal
men (n = 27), normal women (n = 21), men with schizophrenia (n = 27), women
with schizophrenia (n = 13). Permutation test of significant sex x group
interactions in cortical vs subcortical/cerebrospinal fluid regions, demonstrating
significant sex x group effects only in the cortex: P =
.004; SE (P) = .0005; 95% confidence interval, .003-.005).
Overall F test from general linear models for correlated data for sex x
group x area interaction in the cortex: F12,87 = 2.59, P = .005; for subcortical regions: F = 0.30, P = .95. The color coding of the brain regions refers to the following:
pink and red indicate that women have relatively larger volumes (ie, relative
to cerebrum size) than men; light and dark blue indicate that men have relatively
larger volumes than women. The darker the red or blue coloring, the larger
the t value (seen in Table 3). The gray color indicates that men and women were approximately
equivalent in relative volume size. See legend to Figure 1 for explanation
of abbreviations.
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In addition, there were no significant sex differences in asymmetries,
except for the PT. Consistent with previous studies, normal men and women
showed larger left than right-sided PT volumes (mean ± SD, 0.20 ±
0.26 vs 0.17 ± 0.26, respectively; t46 = 0.37; P = .71). Male patients had smaller
volumes on the right, resulting in greater leftward PT asymmetry, than male
normal subjects (0.25 ± 0.23 vs 0.20 ± 0.26; t52 = -0.85; P = .40). The
right side was larger among female patients, resulting in greater symmetry,
than female normal subjects (0.06 ± 0.22 vs 0.17 ± 0.26; t32 = 1.23; P = .23).
The sex x group interaction effect on PT was significant at P.05 (see Table 2).
COMMENT
Our findings show sex-specific effects in schizophrenia in cortical
regions found to be normally sexually dimorphic and abnormal in schizophrenia.
There were no significant differential sex effects in subcortical gray matter
regions or CSF, even though some of these regions have been shown to be normally
sexually dimorphic. This suggests that sex-specific effects in schizophrenia
may be confined primarily to the cortex.
The findings are consistent with, and extend, recent work demonstrating
sex differences in these brain regions.11, 24, 43, 77
This includes the same direction of the effects, such as smaller volumes of
the anterior cingulate gyrus in female patients43, 78
and Heschl's gyrus in male patients11 and larger
volumes of the inferior parietal lobe79 and
right PT77 in female patients. Consistent with
recent work,24 the middle frontal gyrus was
smaller in cases of both sexes, even though we found a larger effect size,
although nonsignificant, among the men. Furthermore, abnormal asymmetry of
the PT in males is consistent with numerous imaging17, 25, 53, 77, 80
and postmortem19-20 studies, and
in females, with right-sided abnormalities.53, 77
The main limitation of this study is the relatively small sample size,
particularly the women; thus, replication is necessary. However, we would
argue that the question of adequate statistical power, and thus the validity
of our negative results, is addressed by the significant overall test of the
cortical sex x group interaction effects, sex differences in effect
sizes, and consistency of findings with previous studies, even the variable
direction of the sex effects. We would argue that low statistical power does
not explain the lack of significant sex differences in hippocampal, basal
ganglia, and ventricular volumes, for which there was adequate power to test
for interaction effects.60 Furthermore, although
3-mm scans were analyzed in this study compared with recent acquisitions of
1.5 mm, our findings are consistent with studies using 1.5 mm. Finally, we
had the unique advantage of simultaneously analyzing, within the same person,
a large number of brain regions, in particular, across the entire cortex,
allowing for tests of the specificity of abnormalities across the cerebrum
in men and women. We have extended previous work by providing a heuristic
model for examining sex differences across the entire brain.
Sex-specific effects in the cortex are interesting, since we found significant
normal sexual dimorphisms in these cortical regions.36
This suggests that factors that contribute to producing normal sexual dimorphisms
may be the same factors that modulate brain abnormalities in schizophrenia.
The impact of sex steroid hormones on brain development, particularly during
late gestation and early postnatal sexual differentiation of the brain,33, 81 may contribute to understanding the
mechanisms responsible for these sex-specific cortical effects, since this
is the same developmental timing implicated in schizophrenia and the initiation
of cortical differentiation. Potential mechanisms32
include epigenetic hormonal factors (eg, secretion of testicular testosterone),
sex-specific genetic programs affecting early sexual brain differentiation,
regulation of apoptosis by androgens, and the colocalization of gonadal receptors
with neurotransmitters, such as the monoamines and  -aminobutyric acid,
and nerve growth factors.
We are not proposing that the fetal or early postnatal periods are the
only periods that may contribute to understanding sex effects in schizophrenia,
since, for example, "activational effects" of circulating hormones, occurring
later in development, eg, during puberty, may or may not potentiate neural
circuits laid down during early development.32
This may be particularly important for the cortex, since it fully develops
later than do subcortical regions. It is interesting that the sex-specific
abnormalities for the dorsolateral and orbital prefrontal cortices were not
as large as for other hypothesized cortical regions. Animal studies have shown
that the level of sex steroid receptors in these two regions does not recede
as dramatically as that in other cortical regions postnatally.33-34
This suggests that there may be relatively greater continuing hormonal effects
on these brain regions influencing plasticity than on other cortical regions.
It is difficult to hypothesize the directions of the sex effects across
the entire brain, since they may depend differentially on the timing of the
insult, the interconnections between brain regions, and their differential
plasticity to early insults (affected by circulating hormones82-83).
Variation in the sex effects may also be due to tissue differences across
brain regions and the fact that the modulations of the impact of early brain
insults by differential gonadal hormone mechanisms may be nonlinear, ie, modified
only given a particular level or threshold of hormonal exposure in a particular
brain region or specific nuclei within it. Although this is not a study of
developmental mechanisms, the results suggest potential hypotheses about sex
effects, timing of insults, and consequences for brain morphologic features
that can be tested in animal models in future studies. Thus, an understanding
of sex-specific brain abnormalities in schizophrenia may lead to etiologic
clues, in addition to understanding the normal properties of the male and
female brain in the face of disease.
Finally, sex differences in cortical abnormalities must be related to
cognitive and symptomatologic differences between men and women with schizophrenia.24, 45, 77-78,84-86
For example, Heschl's gyrus, PT, and Broca's area are brain regions involved
in, among other things, primary auditory processing, language comprehension,
and verbal learning, respectively. We and others have showed some preservation
of function in language and verbal memory in women with schizophrenia,7, 56 which may be related to sex differences
in brain abnormalities.24, 45, 77, 85
Our future work will relate volumetric sex differences reported in this study
to sex differences in cognitive function.
In summary, we report herein that sex-specific volumetric brain abnormalities
are primarily in the cortex. These brain regions are normally sexually dimorphic
and abnormal in schizophrenia. This finding suggests that factors that produce
normal sex differences in brain morphologic features may be modulating insults
producing schizophrenia. Furthermore, the specificity for the cortex may implicate
fetal or early postnatal timing, since this is similar to the timing of risk
factors for schizophrenia, the beginnings of sexual differentiation of the
brain, and the initiation of cortical differentiation.
AUTHOR INFORMATION
Accepted for publication August 13, 2001.
This study was supported by grant RO1 MH56956 (Dr Goldstein) (which
was, in part, supported by the National Institutes of Health Office of Research
on Women's Health) and Merit Awards MH 43518 and 46318 (Dr Tsuang) from the
National Institute of Mental Health, Bethesda, Md.
An earlier version of this work was presented in part at the International
Congress on Schizophrenia Research, Santa Fe, NM, April 19, 1999.
We thank Andrea Boehland, Camille McPherson, and Jason Tourville for
the assessments of brain volumes; Andrea Boehland for figure presentations;
Christine Fetterer for manuscript preparation; and Stuart Tobet, PhD, for
his insightful comments on an earlier version of the manuscript.
Corresponding author and reprints: Jill M. Goldstein, PhD, Massachusetts
Mental Health Center, Harvard Institute of Psychiatric Epidemiology and Genetics,
74 Fenwood Rd, Boston, MA 02115 (e-mail: jill_goldstein{at}hms.harvard.edu).
From the Harvard Medical School Department of Psychiatry at Massachusetts
Mental Health Center, Boston (Drs Goldstein, Seidman, Faraone, and Tsuang);
Veterans Affairs Boston Healthcare System, Brockton, Mass (Drs Goldstein,
Seidman, Faraone, and Tsuang); Harvard Institute of Psychiatric Epidemiology
and Genetics (Drs Goldstein, Seidman, Faraone, and Tsuang); Departments of
Biostatistics (Mr O'Brien) and Epidemiology (Dr Tsuang), Harvard School of
Public Health; Department of Epidemiology and Biostatistics, School of Public
Health, and School of Medicine, Boston University (Dr Horton); and Departments
of Neurology and Radiology Services, Center for Morphometric Analysis, Harvard
Medical School, Massachusetts General Hospital (Drs Kennedy, Makris, and Caviness),
Boston.
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