Executive Function in Individuals With Subthreshold Autism Traits

Abstract

Recent research has documented increased psychosocial difficulties in individuals who report higher-than-typical autistic traits but without an Autism Spectrum Disorder (ASD) diagnosis. Less is known, however, regarding the cognitive profile of individuals with subthreshold autism symptomatology. The objective of the present study was to provide additional insight into this issue and examine whether young adults who report higher degrees of autism traits also report experiencing increased difficulties with executive control.
The Behavior Rating Inventory of Executive Function was utilized to evaluate behavioral aspects of executive functioning in 66 and 28 individuals who endorsed high and low subthreshold levels of autism symptomatology, respectively.
After accounting for Attention Deficit/Hyperactivity Disorder (ADHD) symptomatology at both the group and individual participant levels, we found that autism traits continued to explain a significant amount of variance in participants' overall level of executive function (Global Executive Composite) as well as within most individual executive domains. Interestingly, the high and low trait groups did not differ on the inhibitory control and organization of materials scales, areas of functioning that appears to be largely spared in individuals with ASD as well.
Findings from the present study are consistent with past research linking ASD and executive control impairment. In addition, ASD and ADHD traits were associated with unique contributions to the executive control profile of individuals with subthreshold autism symptomatology. This finding underscores the importance of accounting for ADHD symptomatology in studying ASD.

Full text

Executive Function in Individuals With Subthreshold Autism Traits
Shawn E. Christ and Stephen M. Kanne
University of Missouri Angela M. Reiersen
Washington University School of Medicine
Objective: Recent research has documented increased psychosocial difficulties in individuals who report
higher-than-typical autistic traits but without an Autism Spectrum Disorder (ASD) diagnosis. Less is
known, however, regarding the cognitive profile of individuals with subthreshold autism symptomatol-
ogy. The objective of the present study was to provide additional insight into this issue and examine
whether young adults who report higher degrees of autism traits also report experiencing increased
difficulties with executive control. Method: The Behavior Rating Inventory of Executive Function was
utilized to evaluate behavioral aspects of executive functioning in 66 and 28 individuals who endorsed high
and low subthreshold levels of autism symptomatology, respectively. Results: After accounting for Attention
Deficit/Hyperactivity Disorder (ADHD) symptomatology at both the group and individual participant levels,
we found that autism traits continued to explain a significant amount of variance in participants’ overall level
of executive function (Global Executive Composite) as well as within most individual executive domains.
Interestingly, the high and low trait groups did not differ on the inhibitory control and organization of materials
scales, areas of functioning that appears to be largely spared in individuals with ASD as well. Conclusions:
Findings from the present study are consistent with past research linking ASD and executive control
impairment. In addition, ASD and ADHD traits were associated with unique contributions to the executive
control profile of individuals with subthreshold autism symptomatology. This finding underscores the
importance of accounting for ADHD symptomatology in studying ASD.
Keywords: autism spectrum disorder, executive control, broader autism phenotype, attention deficit/
hyperactivity disorder, Behavior Rating Inventory of Executive Function
Autism may be best conceptualized as a spectrum disorder
characterized by varying degrees of social and communicative
impairment often coupled with a tendency to engage in repet-
itive behaviors and/or restricted interests (American Psychiatric
Association, 2000). Recent work suggests that affected individ-
uals may include not only those with autism, Asperger’s, and
Pervasive Developmental Disorder–Not Otherwise Specified
(PDD-NOS), but also individuals who exhibit higher-than-typ-
ical degree of autism symptomatology but who do not meet
formal diagnostic criteria.
Much of the evidence for the existence of a more general
autism phenotype comes from research involving relatives of
individuals with Autism Spectrum Disorder (ASD). For exam-
ple, Piven, Palmer, Jacobi, Childress, and Arndt (1997) reported
higher rates of social and communicative difficulties among
relatives of families with multiple ASD-diagnosed siblings as
compared to relatives of families with an offspring with Down’s
syndrome. Interestingly, the pattern of impairment reported for
the ASD relatives was similar to that observed in individuals
with autism, just more subtle. Landa, Holman, and Garrett-
Mayer (2007) documented a slight language delay in undiag-
nosed siblings of children with autism. Bishop et al. (2004)
found that parents of individuals with ASD scored significantly
higher than parents of individuals without ASD on the Autism-
Spectrum Quotient (AQ), a brief self-report questionnaire de-
signed to evaluate autism traits in individuals with normal
intelligence (Baron-Cohen, Wheelwright, Skinner, Martin, &
Clubley, 2001). Utilizing the Social Responsiveness Scale
(SRS), a questionnaire designed to assess the social difficulties
associated with ASD, Constantino et al. (2004) reported higher-
than-typical rates of subthreshold autism traits among undiag-
nosed siblings of children with ASD. Taken together, the find-
ings from these studies and others support the hypothesis that
relatives of individuals with autism may carry a genetic liability
for autism that leads to the expression of the broader autism
phenotype (BAP), a set of cognitive and behavioral character-
istics that are qualitatively similar to autism but less severe
(e.g., Piven & Palmer, 1999; Piven et al., 1997).
1
1
Traditionally, the term “broader autism phenotype” has been reserved
for use in discussing the cognitive and behavioral profile of individuals
with a genetic/familial liability for autism. As such, in the absence of
genetic data for the present participant sample, we have chosen to avoid
using this term to describe the current dataset and findings.
Shawn E. Christ, Department of Psychological Sciences, and Thompson
Center for Autism and Neurodevelopmental Disorders, University of Mis-
souri; Stephen M. Kanne, Department of Health Psychology, and Thomp-
son Center for Autism and Neurodevelopmental Disorders, University of
Missouri; Angela M. Reiersen, Department of Child Psychiatry, Washing-
ton University School of Medicine.
This research was supported by grants from the University of Missouri
Thompson Center for Autism and Neurodevelopmental Disorders (S.E.C.
and S.M.K.) and the University of Missouri Research Board (S.E.C.). We
thank Lauren Kruczyk, Kimberly Pope, Blaine McGuire, and Brittany
Waller for their assistance with data collection; and Amanda Savarese for
her assistance with manuscript preparation.
Correspondence concerning this article should be addressed to Shawn E.
Christ, Department of Psychological Sciences, 210 McAlester Hall, Uni-
versity of Missouri, Columbia, MO 65203. E-mail: christse@missouri.edu
Neuropsychology © 2010 American Psychological Association
2010, Vol. 24, No. 5, 590–598 0894-4105/10/$12.00 DOI: 10.1037/a0019176
590
This document is copyrighted by the American Psychological Association or one of its allied publishers.
This article is intended solely for the personal use of the individual user and is not to be disseminated broadly.

Subthreshold Autism Traits and the
General Population
Additional research suggests that the expression of subthreshold
autism traits may extend beyond those with a family history of
ASD and include the general population. In a study of university
students, Baron-Cohen et al. (2001) found that a subsample of
students (i.e., mathematicians) scored significantly higher on the
AQ as compared to other students (i.e., those studying the human-
ities and social sciences). Across separate studies involving a large
sample of twin pairs (Constantino & Todd, 2003) and child psy-
chiatric patients with and without ASD (Constantino et al., 2004),
Constantino and colleagues found evidence suggesting that autism
traits may lie on a continuum, with symptomatology being con-
tinuously distributed in the general population.
Within this context, a growing number of studies have begun to
investigate individuals with subthreshold autism symptomatology
in hopes of gaining additional insight into the nature of the diffi-
culties experienced by individuals with ASD. The resulting re-
search suggests that the subthreshold autism traits may be associ-
ated with increased risk for psychiatric and psychosocial problems.
For example, Jobe and White (2007) recently reported that in-
creased endorsement of autism-related symptomatology (as mea-
sured by the AQ) in young adults was associated with increased
loneliness and a decrease in the number and duration of friend-
ships. Utilizing the adolescent self-report version of the Behavioral
Assessment System for Children–2nd Edition (BASC-2; Reynolds
& Kamphaus, 2000), a comprehensive measure of psychosocial
and emotional adjustment, Kanne, Christ, and Reiersen (2009)
found evidence of autism trait-related increases across a wide
range of psychiatric and psychosocial problem areas including
depression/anxiety, interpersonal relationships, and personal ad-
justment in otherwise undiagnosed young adults. This finding
parallels past studies showing increased rates of anxiety and de-
pression in individuals with a diagnosed ASD (Kim, Szatmari,
Bryson, Streiner, & Wilson, 2000; Tantam, 2000).
Additional research has focused on whether individuals with
subthreshold autism traits are also at a greater risk for other
comorbid conditions such as Attention Deficit/Hyperactivity Dis-
order (ADHD) that have previously been linked to ASD. Indeed,
approximately 41–78% of individuals with ASD experience symp-
tomatology consistent with ADHD (Gadow, DeVincent, &
Pomeroy, 2006; Goldstein & Schwebach, 2004; Sturm, Fernell, &
Gillberg, 2004). Conversely, children with ADHD (especially
those with inattentive or combined type) have been found to have
elevated levels of autism-related symptomatology (Reiersen, Con-
stantino, & Todd, 2008; Reiersen, Constantino, Volk, & Todd,
2007). Recent research suggests that this commonality may also
extend to individuals with subthreshold traits. In a study involving
child twin pairs, Constantino, Hudziak, and Todd (2003) found
that scores on the Child Behavior Checklist (CBCL; Achenbach,
1991) explained 43% of the variance in SRS scores, with attention
problems contributing the most. Utilizing a self-report versions of
the SRS and an ADHD questionnaire, Reiersen and colleagues
(Reiersen, Constantino, Grimmer, Martin, & Todd, 2008) found a
significant correlation (r⫽.48) between autism traits and ADHD
symptomatology in an unselected sample of 699 Australian young
adult twins.
Executive Control
Both ASD and ADHD are associated with impairments in execu-
tive control (Barkley, 1997; Russell, 1997). Executive control refers to
a set of higher-order cognitive processes that allow for the flexible
modification of thought and behavior in response to changing cogni-
tive or environmental contexts (Stuss, 1992). It encompasses cogni-
tive skills such as planning, strategy use, cognitive flexibility, inhib-
itory control, and working memory. These abilities are considered
“executive” in that they are said to require the integration and pro-
cessing of information from a wide range of internal and external
sources. Executive difficulties in ASD and ADHD are relatively
well-documented. ASD is generally associated with impairments in
cognitive flexibility and shifting (Geurts, Verte, Oosterlaan, Roeyers,
& Sergeant, 2004; Hill, 2004; Kenworthy, Yerys, Anthony, & Wal-
lace, 2008) whereas ADHD is associated more so with inhibitory
control difficulties (Geurts et al., 2004; Pennington & Ozonoff, 1996).
In contrast, much less is known regarding the integrity of executive
control in individuals with subthreshold autism symptomatology.
Past studies on this topic have focused primarily on parents and
siblings of individuals with ASD and have yielded conflicting
results. For example, Wong, Mayberry, Bishop, Maley, and Hall-
mayer (2006) reported that ASD parents and siblings performed
comparable to their control counterparts on the Tower of London
test (a measure of planning and sequencing ability). Other studies
utilizing similar tasks, however, have documented impaired per-
formance for parents and siblings (Parents: Hughes, Leboyer, &
Bouvard, 1997; Piven & Palmer, 1997; Siblings: Hughes, Plumet,
& Leboyer, 1999; Ozonoff, Rogers, Farnham, & Pennington,
1993). The findings on other aspects of executive control such as
cognitive flexibility are also mixed, with some studies reporting
intact performance in first-degree relatives (e.g., Ozonoff et al.,
1993; Szatmari et al., 1993), and others reporting impaired perfor-
mance (e.g., Hughes et al., 1997; Hughes et al., 1999). Recent
research (e.g., Losh & Piven, 2007) suggests that subthreshold
autism traits are not necessarily evident in all first-degree relatives
of a proband and, consequently, inclusion of such “unaffected”
individuals in the aforementioned studies may have contributed to
the variability in findings.
It remains unclear whether executive control is adversely af-
fected in individuals with subthreshold autism traits. In the present
study, we sought to further investigate this issue and examine
whether young adults who report higher degrees of autism traits
also report experiencing increased difficulties with executive con-
trol. Whereas the majority of previous studies have utilized groups
defined based on familial relationship (parent, sibling) to a pro-
band, the present study focused on the relationship between exec-
utive control and subthreshold autism traits within the general
population. We hypothesized that higher levels of autism traits
would be associated with increased executive problems. We also
hypothesized that this relationship would remain significant even
after accounting for variability in executive performance related
ADHD symptomatology.
Method
Participants
A total of 1,847 undergraduate students (Age: M(SD)⫽18.4
(0.97); Sex: 37.3% men) were enrolled in an introductory psychol-
591SUBTHRESHOLD AUTISM TRAITS & EXECUTIVE DYSFUNCTION
This document is copyrighted by the American Psychological Association or one of its allied publishers.
This article is intended solely for the personal use of the individual user and is not to be disseminated broadly.

ogy course and completed a self-report screening version of the
SRS and a brief ADHD symptom questionnaire as part of a larger
survey in return for course credit. (See below for detailed descrip-
tions of both questionnaires.) Additional demographic information
for the participant sample is included in Table 1.
Responses on the screening SRS were then used to identify 85
individuals who reported a higher-than-typical degree of autism-
related traits (top 5th percentile; Total SRS score ⫽⬎13; high trait
group) as compared to their peers. We also identified a comparison
group of 259 individuals who were matched to the high trait group
for age and sex, but who reported few if any autism-related traits
(Total SRS score ⫽⬍6; low trait group). Consistent with previous
research (Reiersen, Constantino, Grimmer, et al., 2008), prelimi-
nary analyses of the present dataset revealed a positive correlation
(r⫽.44, p⬍.0001) between scores on the SRS and the ADHD
questionnaire. As such, the selected groups were also matched on
ADHD score thus allowing us to focus on possible executive
difficulties above and beyond those associated with comorbid
attention symptomatology.
A sample of 45 and 75 individuals from the aforementioned
high and low trait groups, respectively, agreed to also complete an
extended neuropsychological battery in return for additional
course credit. (The current study was just one of several possible
studies that students had the option of choosing to participate in to
receive their course credit. As such, the disparity between the
number of “identified” potential participants and those that actu-
ally participated does not reflect attrition in the traditional sense.)
Because of the length of time between completing the survey
and participating in the remainder of the study (i.e., ⬃2–3 months),
and to guard against the possibility that their initial responses were
biased for inclusion in later studies (e.g., class credit), these 120
participants were readministered the screening SRS at the time of
the neuropsychological testing session. The correlation between
the initial and later SRS was significant (r⫽.78, p⬍.05).
Participants were excluded if their group membership changed
based on their second SRS score or if their score overlapped with
the other group (e.g., no participant in the high trait group had a
lower 2nd SRS score than a participant in the low trait group;
n⫽16).
Participants were also screened for significant psychiatric or
medical history related to ASD, ADHD, or other neurological
conditions. Ten additional individuals were excluded on this basis
(8 ⫽ADHD; 1 ⫽Anxiety Disorder, 1 ⫽Depression). None of the
participants (across both groups) reported that they had received a
diagnosis of ASD. The final sample comprised 28 individuals in
the high trait group and 66 individuals in the low trait group.
The study battery included measures of overall intellectual
ability (i.e., Wechsler Abbreviated Scale of Intelligence; WASI),
autism symptomatology (i.e., SRS, AQ), ADHD symptomatology
(i.e., a 12-item questionnaire described below), psycho-emotional
adjustment (i.e., BASC-2), and executive functioning (i.e., Behav-
ior Rating Inventory of Executive Function; BRIEF). Administra-
tion of the entire battery took ⬍2 hr, during which time partici-
pants were offered frequent breaks. The test of intellectual ability
(which was presumed to be more susceptible to potential fatigue
effects than the other measures) was administered first, followed
by the questionnaire measures.
Data from the study battery related to psycho-emotional adjust-
ment has been reported elsewhere (Kanne et al., 2009). Presently,
we focused on the previously unreported data related to executive
functioning in these individuals.
Measures
SRS. The SRS (Constantino, Davis, et al., 2003) is a parent/
teacher report measure that assesses autistic traits. The question-
naire includes 65 items that assess the child’s engagement in
reciprocal social interactions, understanding of emotional and so-
cial cues, and motivation to engage with others. Although the SRS
focuses on social behaviors, it includes items related to all three
autism symptom domains of social impairment, communication
impairment, and stereotyped/repetitive behaviors.
Psychometric studies of the SRS indicate that scores are con-
tinuously distributed across the general population, and that the
SRS shows good test–retest reliability (Constantino, Davis, et al.,
2003; Constantino, Przybeck, Friesen, & Todd, 2000; Constantino
& Todd, 2000, 2003), interrater reliability (Pine, Luby, Abbacchi,
& Constantino, 2006), discriminant validity (Constantino et al.,
2000; Constantino & Todd, 2000, 2003), and concurrent validity
(Constantino et al., 2003).
Because of time constraints, limitations were placed on the
questionnaire length that could be included in the large initial
survey. Within this context, we utilized a brief, self-report screen-
ing version of the SRS that was recently developed and adminis-
tered as part of a separate study of young adult Australian twins
(Reiersen, Constantino, Grimmer, et al., 2008). This screening
version consisted of 11 Self-Report SRS items wherein respon-
dents rated items on a 4-point Likert Scale (0 ⫽False, not at all
true; 1 ⫽Slightly true; 2 ⫽Mainly true; 3 ⫽Very true) covering
a range of ASD traits. The original versions of these 11 SRS items
(based on SRS items 6, 15, 16, 18, 24, 29, 35, 37, 39, 42, and 58)
all had high loadings on the first unrotated factor of a principal
components analysis completed in a sample of children and ado-
lescents, and items from each of the three autism symptom do-
Table 1
Demographics, Screening SRS Scores, AQ Scores, and IQ
Estimates of Low and High Trait Groups and the Total Sample
Low trait
(n⫽66) High trait
(n⫽28) Total sample
(N⫽1847)
Age
Mean (SD) 18.2 (0.55) 18.7 (0.95) 18.4 (0.97)
Range 18–21 17–21 17–33
Sex (% men) 47.0 50.0 37.3
Ethnicity (% White) 92.4 82.1 88.1
Screening SRS total score
Mean (SD) 2.2 (1.7) 17.6 (3.5) 4.6 (4.3)
Range 0–5 14–25 0–25
Screening ADHD total score
Mean (SD) 14.2 (5.6) 14.3 (6.3) 9.3 (6.6)
Range 1–32 2–25 0–36
AQ total score
Mean (SD) 13.2 (4.8) 24.3 (4.4) —
Range 3–23 16–35 —
Estimated IQ
a
Mean (SD) 106.3 (8.5) 110.1 (7.5) —
Range 83–126 93–130 —
a
Based on the WASI (Psychological Corporation, 1999).
592 CHRIST, KANNE, AND REIERSEN
This document is copyrighted by the American Psychological Association or one of its allied publishers.
This article is intended solely for the personal use of the individual user and is not to be disseminated broadly.

mains (social impairment, language impairment, and stereotyped/
repetitive behaviors) were included. The item wording was mod-
ified for self-report, and higher scores indicate more severe
symptomatology.
ADHD questionnaire. A 12-item self-report measure of
DSM–IV ADHD inattentive and impulsive symptoms was also
administered. (Regretfully, time constraints related to the larger
initial survey again prohibited the use of a more comprehensive
measure.) This questionnaire has been used previously to examine
the relationship between self-report SRS and ADHD symptom-
atology in young adult Australian twins (for more detailed descrip-
tion, see Reiersen, Constantino, Grimmer, et al., 2008). Similar to
the self-report SRS, respondents rated items on a 4-point Likert
Scale (0 ⫽False, not at all true; 1 ⫽Slightly true; 2 ⫽Mainly
true; 3 ⫽Very true). Higher scores reflect more severe symptom-
atology.
AQ. The AQ (Baron-Cohen et al., 2001) is a self-report mea-
sure that assesses the presence of autistic traits in adults with
normal intelligence. The report consists of 50 items assessing traits
associated with ASD including social skills, attention switching,
attention to detail, communication, and imagination. Psychometric
study of the AQ indicated good test–retest reliability and internal
consistency (Baron-Cohen et al., 2001) as well as good discrimi-
native validity (Woodbury-Smith, Robinson, Wheelwright, & Bar-
on-Cohen, 2005). Higher scores reflect more severe symptomatol-
ogy.
WASI. The Vocabulary and Matrix Reasoning subtests from
the WASI (Psychological Corporation, 1999) were administered to
estimate general intellectual ability.
BRIEF. The BRIEF is a standardized questionnaire designed
to assess executive function within the context of an individual’s
day-to-day environment (Gioia, Isquith, Guy, & Kenworthy, 2000;
Gioia, Isquith, Kenworthy, & Barton, 2002). Presently, we utilized
the standardized adult self-report version (Roth, Isquith, & Gioia,
2005). (Parent/teacher report versions are also available for use
with younger samples.)
The questionnaire consists of 75 items assessing behavioral
manifestations of executive problems in daily life. Items comprise
nine nonoverlapping clinical scales reflecting different aspects of
executive function including inhibitory control, self-monitoring
ability, planning and organizational skill, emotional control, and
working memory. In addition, two broader indices (Behavioral
Regulation Index, BRI; Metacognition Index; MI) as well as an
overall index reflecting overall executive ability (Global Executive
Composite; GEC) can be computed. The Inhibit, Shift, Emotional
Control, and Self-Monitor clinical scales contribute to the BRI;
and the Initiate, Working Memory, Plan/Organize, Task Monitor,
and Organization of Materials clinical scales contribute to the MI.
The BRI and MI are then used to compute the GEC. The tscores
for each index score were computed (Roth et al., 2005) and served
as the dependent variable.
Results
Subthreshold Autism Traits
SRS score correlated highly with AQ total score, r⫽.75, p⬍
.001. The SRS and AQ scores for the high trait group (M⫽17.6
and 24.3, respectively) were significantly higher than those for the
low trait group (M⫽2.2 and 13.2, respectively), t(92) ⫽28.8
and 10.4, respectively, p⬍.001 in both instances.
Demographic Variables and Our Statistical Approach
The high and low trait groups were well-matched for sex,
Mann–Whitney U⫽896.0, p⫽.79. Although the groups differed
slightly on estimated IQ (High trait group: M⫽110; Low trait
group: M⫽106), t(92) ⫽2.06, p⬍.05, IQ did not correlate with
ADHD score or any of the BRIEF indices (p⬎.15 in all in-
stances). Consequently, sex and IQ were excluded from further
analyses.
Consistent with past research that indicated a strong association
between ADHD symptomatology and executive ability, scores on
the ADHD questionnaire within both groups were significantly
correlated with 11 of the 12 BRIEF indices (r⬎.25, p⬍.05 in all
instances). We adopted a conservative approach in the current
analysis by including ADHD scores in the subsequent statistical
model in addition to the initial matching between high and low
trait groups on ADHD scores. Using regression analyses allowed
us to (1) account for variability in executive control related to
individual differences in ADHD symptomatology and (2) evaluate
whether the relationship between autism traits and executive con-
trol varies with respect to the severity of ADHD symptomatology
(i.e., an interaction between ADHD score and trait group).
A series of hierarchical regression analyses were conducted,
with each BRIEF index score serving as the dependent variable in
turn. ADHD score was entered in the first step of the model,
followed by group (high trait and low trait) in the next step. The
interaction variable (ADHD score X Group) was entered in the
third step. By utilizing this approach, we were able to partial out
variability in executive control related to ADHD symptomatology.
The portion of remaining variance attributable solely to sub-autism
traits could then be identified (i.e., partial correlation; pr
2
). To
protect against an increase in the likelihood of a Type I error
related to multiple comparisons, we confirmed a significant group
effect on GEC before proceeding to analyzing the contributing
index scores (BRI and MI). Similarly, significant group effects on
BRI and MI were confirmed before analyzing the contributing
clinical scales.
Mean BRIEF scores for both groups are shown in Figure 1. The
results of the regression analyses are summarized in Table 2.
Contribution of ADHD Symptomatology to
Executive Control
As can be seen in Table 2, ADHD scores accounted for a
significant portion of individual variability in all three composite
executive control indices (GEC, BRI, and MI) and all but one of
the clinical scales (Shift scale: R
2
⫽0.02, p⫽.14; all other
instances p⬍.05). The largest effect sizes were observed for the
Plan/Organize scale (R
2
⫽0.30, p⬍.001) and the Working
Memory scale (R
2
⫽0.27, p⬍.001).
Autism Traits and Executive Control
The high trait group scored significantly higher than the low trait
group on all three executive control composite indices, F(1,
91) ⬎15.5, p⬍.001 in all instances. Trait group membership
593SUBTHRESHOLD AUTISM TRAITS & EXECUTIVE DYSFUNCTION
This document is copyrighted by the American Psychological Association or one of its allied publishers.
This article is intended solely for the personal use of the individual user and is not to be disseminated broadly.

accounted for 24.2, 23.8, and 14.6% of the variance in GEC, BRI,
and MI scores, respectively, after removing the contributions of
ADHD scores.
Group-related differences were also apparent on seven of the
nine clinical scales, F(1, 91) ⬎6.6, p⬍.05 in all instances. The
largest effect size was observed for the Shift scale with trait group
accounting for 33.6% of the variance above and beyond that
associated with ADHD scores, F(1, 91) ⫽46.2, p⬍.001. As can
be seen in Figure 2, 36% of the high trait group scored within the
‘clinically significant’ range (tscore ⬎65) on the Shift scale as
compared to 0% of the low trait group. Conversely, group mem-
bership did not contribute significantly to scores on the Inhibit and
Organization of Materials scales, F(1, 91) ⬍1, p⬎.5 in both
instances.
An interaction variable was also included in the present statis-
tical model to determine if group-related differences in executive
control varied as a function of the level of ADHD symptomatology
reported. An interaction between trait group and ADHD score was
not present for any of the BRIEF scores (p⬎.05 in all instances).
As can be seen in Figure 3, a similar relationship between ADHD
score and GEC composite index was observed for both trait groups
(high and low).
Additional Confirmatory Analyses
Additional analyses confirmed that substitution of raw SRS or
AQ scores (in place of high/low trait group membership) in the
previously described regression model yielded comparable results.
Figure 1. Mean BRIEF index scores shown separately for each group (low trait, high trait). Error bars represent
SEM.
Table 2
Hierarchical Regression Analysis Predicting BRIEF Index Scores From ADHD Score and Group Membership
(High Trait and Low Trait)
Dependent variable
Step 1 Step 2
ADHD score Group
R
2
⌬F(1, 92) R
2
⌬R
2
pr
2
⌬F(1, 91)
Global Executive Composite 0.32 43.86
ⴱⴱⴱ
0.49 0.16 0.24 29.00
ⴱⴱⴱ
Behavioral Regulation Index 0.18 20.80
ⴱⴱⴱ
0.38 0.19 0.24 28.40
ⴱⴱⴱ
Metacognition Index 0.33 44.70
ⴱⴱⴱ
0.43 0.10 0.15 15.53
ⴱⴱⴱ
Clinical scales
Inhibit 0.22 25.53
ⴱⴱⴱ
0.22 0.006 0.007 ⬍1
Shift 0.02 2.17 0.35 0.33 0.34 46.17
ⴱⴱⴱ
Emotional Control 0.07 6.38
ⴱ
0.28 0.21 0.23 27.05
ⴱⴱⴱ
Self-Monitor 0.21 24.38
ⴱⴱⴱ
0.29 0.08 0.10 9.84
ⴱⴱ
Initiate 0.17 19.28
ⴱⴱⴱ
0.33 0.15 0.18 20.39
ⴱⴱⴱ
Working Memory 0.27 33.72
ⴱⴱⴱ
0.32 0.05 0.07 6.65
ⴱ
Plan/Organize 0.30 39.35
ⴱⴱⴱ
0.40 0.10 0.14 14.69
ⴱⴱⴱ
Task Monitor 0.25 30.04
ⴱⴱⴱ
0.39 0.14 0.19 20.89
ⴱⴱⴱ
Organization of Materials 0.16 17.28
ⴱⴱⴱ
0.17 0.008 0.009 ⬍1
ⴱ
p⬍.05.
ⴱⴱ
p⬍.005.
ⴱⴱⴱ
p⬍.001.
594 CHRIST, KANNE, AND REIERSEN
This document is copyrighted by the American Psychological Association or one of its allied publishers.
This article is intended solely for the personal use of the individual user and is not to be disseminated broadly.

Consistent with findings from the group-based analysis, SRS/AQ
score accounted for a significant amount of variance in all three
BRIEF composite indices and seven of the nine clinical scales (all
⌬R
2
s⬎0.04, p⬍.05 in all instances). The largest effect size
continued to be observed for the Shift scale (⌬R
2
s⬎0.33, p⬍
.001 in both instances). Conversely, neither SRS score nor AQ
score contributed significantly to the Inhibit or Organization of
Materials scales (all ⌬R
2
s⬍0.01, p⬎.2 in all instances).
To rule out the possibility that the observed relationships be-
tween SRS and BRIEF scores were due simply to an overlap in
item content (e.g., both measures include items assessing attention
shifting); we also repeated the regression analysis using a com-
posite score comprising only “noncognitive” SRS items (SRS
Items 24, 35, and 58 were omitted). The findings were virtually
identical to those described previously, and the relationship be-
tween the noncognitive SRS subscore and the BRIEF Shift scale
remained strong (⌬R
2
⫽0.32, p⬍.001). Similar results were also
found when substituting in the AQ social skill subscore (i.e., sum
score of items 1, 11, 13, 15, 22, 36, 44, and 45; Baron-Cohen et al.,
2001).
Lastly, consistent with the present focus on subthreshold autism
traits, none of the included participants reported having been
previously diagnosed with an ASD. Two of the participants in the
high trait group, however, scored above the clinical cutoff (32⫹)
for autism traits as measured by the AQ (Baron-Cohen et al.,
2001). Whereas a score above the cutoff does not necessarily mean
there is a diagnosable disorder (i.e., a diagnosis would be merited
only if the symptoms gave rise to significant distress in the pa-
tient’s day-to-day life), in the absence of a full diagnostic assess-
ment it remains possible that these two individuals may have met
diagnostic criteria for an ASD. With this in mind, the regression
analyses were repeated while excluding data from these partici-
pants. The resulting pattern of findings as well as the magnitude of
the observed relationships between autistic traits and BRIEF
scores remained largely unchanged (e.g., GEC: ⌬R
2
⫽0.18, p⬍
.001; Shift scale: ⌬R
2
⫽0.32, p⬍.001).
Unlike with the AQ, a cutoff score has not yet been established
for the screening version of the SRS. As can be seen in Figure 2,
however, the inclusion of individuals who scored exceptionally
high on the SRS screening measure also does not appear to be
driving the relationship between scores on this measure and the
BRIEF either. Taken together, this observation and the previously
described analyses argue against the possibility that the present
findings are attributable to the unintentional inclusion of individ-
uals with a diagnosable ASD in the present participant sample.
Discussion
Whereas the cognitive difficulties experienced by individuals
with ASD are well documented, much less is known regarding the
cognitive profile of individuals with subthreshold autism traits. In
the present study, we evaluated executive functioning, an area of
cognitive skill that is particularly impaired in individuals with
ASD (Hill, 2004; Russell, 1997), in individuals with subthreshold
autism traits.
As noted earlier, prior research (Reiersen, Constantino, Grim-
mer, et al., 2008; Ronald, Simonoff, Kuntsi, Asherson, & Plomin,
2008; Sturm et al., 2004) suggests that ASD and ADHD may share
a common genetic influence, and that this relationship may extend
to individuals within the more general autism phenotype (Con-
stantino, Hudziak, et al., 2003; Reiersen, Constantino, Grimmer, et
al., 2008). Consistent with this, we found a robust correlation (r⫽
.44) between the degree of autistic and ADHD symptomatology
among participants in the present study.
Past studies have also documented executive control impairment
in individuals with ADHD (for review, see Willcutt, Doyle, Nigg,
Faraone, & Pennington, 2005). For example, utilizing the parent-
and teacher-report versions of the BRIEF, Gioia et al. (2002) found
that children with ADHD-Combined Type exhibited increased
Figure 3. A scatter plot showing each participant’s Global Executive
Composite (GEC) index score as a function of his or her ADHD question-
naire score. Each group (low trait, high trait) and corresponding linear
regression lines (solid and dashed, respectively) are shown separately.
Figure 2. A scatter plot showing each participant’s BRIEF Shift clinical
scale score as a function of his or her SRS screening questionnaire score.
Each group (low trait, high trait) is shown separately. The dashed reference
line denotes a t score of 65; scores above this threshold are considered
‘clinically significant’ (Roth et al., 2005).
595SUBTHRESHOLD AUTISM TRAITS & EXECUTIVE DYSFUNCTION
This document is copyrighted by the American Psychological Association or one of its allied publishers.
This article is intended solely for the personal use of the individual user and is not to be disseminated broadly.

executive difficulties as compared to typically developing children
across all of the BRIEF scales. Children with ADHD-Inattentive
Type were found to show significant problems in all domains
except for the ability to shift freely from one problem/situation to
another (i.e., Shift Index). In the present study utilizing adult
self-report versions of the BRIEF and an ADHD questionnaire, we
also found that increased ADHD symptomatology was associated
with increased executive difficulties across all domains except the
Shift Index.
2
Within this context, it remains unclear to what extent concom-
itant ADHD symptomatology may contribute to potential execu-
tive difficulties experienced by individuals with sub-autism traits.
To address this issue, we recruited two groups of participants who
were matched on their degree of ADHD symptoms but who
reported either a high or low amount of autism-related symptom-
atology. After accounting for ADHD symptomatology at both the
group and individual participant levels, we found that autism traits
continued to explain a significant amount of variance in partici-
pants’ overall level of executive function (Global Executive Com-
posite) as well as within several individual executive domains.
Increased endorsement of autism traits was associated with in-
creased difficulties with shifting from one problem/situation to
another (Shift Index); appropriately modulating emotional re-
sponses (Emotional Control Index); initiating new tasks or activ-
ities (Initiate Index); planning, organizing, and setting goals (Plan/
Organize Index); and making careless errors and completing work
(Task Monitor Index). Working memory and the ability to monitor
one’s own behavior were also related to autism symptomatology
but to a lesser degree. In contrast, inhibitory control, or the ability
to control impulses and inhibit inappropriate behavior, was not
associated with responses on the autism questionnaire. The ten-
dency to keep one’s work space and materials orderly (Organiza-
tion of Materials Index) was also unrelated to autism symptom-
atology.
The present pattern of results is generally consistent with the
existing literature on executive control and ASD. Prior research on
working memory and inhibitory control in individuals with ASD
suggests that ASD-related impairments in these areas are not
pervasive but rather appear to be circumscribed to particular as-
pects of inhibition and working memory (e.g., Christ, Holt, White,
& Green, 2007; Luna et al., 2002). With regards to the Organiza-
tion of Materials Index, findings from previous ASD studies uti-
lizing the parent-report version of the BRIEF (e.g., Gilotty, Ken-
worthy, Sirian, Black, & Wagner, 2002; Gioia et al., 2002; Zandt,
Prior, & Kyrios, 2009) suggest that scores for children with ASD
may be less elevated on this scale as compared to the other index
scores. As such, the finding of weaker relationships between these
executive domains and the degree of autism symptomatology is
not surprising.
The present findings support the hypothesis that autism traits are
related to executive function above and beyond any association
with comorbid ADHD symptomatology. Further, each neurodevel-
opmental trait (autism and ADHD) is associated with a unique
pattern of sparing/impairment across executive domains. For ex-
ample, although the ability to shift from one problem/situation to
another was strongly associated with autism symptomatology
(⌬R
2
⫽0.33), there was little if any observed relationship between
this ability and ADHD score (R
2
⫽0.02, ns). Individual differ-
ences in autism trait score also explained a large amount of
variance in emotional control ability (⌬R
2
⫽0.21); however,
ADHD scores contributed only minimally to this area of function-
ing (R
2
⫽0.07). Conversely, whereas there was a strong relation-
ship between ADHD score and both inhibitory control and the
extent to which one is organized (R
2
⫽0.22 and 0.16, respec-
tively), the autism trait measure did not make a unique contribution
to either executive domain (⌬R
2
⬍0.01 in both cases, ns).
Of note, the current results documenting unique contributions to
executive function by autism and ADHD traits appear to parallel
recent findings in the behavioral genetics field. Specifically, a
handful of twin studies (Constantino & Todd, 2003; Reiersen,
Constantino, Grimmer, et al., 2008; Ronald et al., 2008) have
shown that, whereas autism and ADHD do indeed share common
genetic influences, there is also a unique genetic influence associ-
ated with each condition. One may postulate that the patterns of
autism- and ADHD-related sparing/impairment in executive func-
tion observed in the present study may represent the phenotypic
expression of the unique genetic influences related to autism and
ADHD that were documented in the aforementioned twin studies.
From a neurophysiological standpoint, the current findings are also
consistent with the theory that the executive impairments associ-
ated with autism and ADHD arise out of disruption of the same
general neural network (i.e., frontostriatal pathways) but that the
timing, severity, and precise locus of such damage may differ
between the two conditions (Bradshaw, 2001; Bradshaw & Shep-
pard, 2000) thus leading to partial but not complete overlap in their
neurocognitive profiles.
The current study focused on individuals with subthreshold
autism symptomatology. Consistent with this, none of the partic-
ipants had been previously diagnosed with an ASD (as per self-
report), and only two individuals (both in the high trait group)
scored above the high cutoff (32⫹) for autism traits as measured
by the AQ (Baron-Cohen et al., 2001). In contrast, 79% of the high
trait group (in comparison to only 33% of the low trait group)
scored in the ‘clinically significant’ range (tscore ⬎65) on two or
more BRIEF subscales. (For the Shift scale alone, the percentage
of clinical significant scores for the high and low trait groups
was 36 and 0%, respectively).
3
Although speculative, this finding
suggests that even in the absence of marked social and communi-
cative impairment (as would be evidenced by an ASD diagnosis),
individuals with subthreshold autism traits may be at greater risk
than the general population for cognitive difficulties.
Taken together, the current findings support the hypothesis that
individuals with diminished autism-related symptoms may experience
a similar pattern of executive dysfunction (albeit less severe) to that
experienced by individuals with ASD. Further, to the extent that
undiagnosed individuals with subthreshold autism traits tend to be
2
Given that (1) the brief ADHD questionnaire used in the present study
assessed primarily inattentive and impulsive symptoms, and (2) individuals
who had previously received a diagnosis of ADHD (as per self-report)
were excluded from participation; it is unlikely that the present sample
included individuals with severe ADHD-Combined Type.
3
There was an overall trend for higher BRIEF scores (i.e., more exec-
utive difficulties) across both ASD trait groups (low and high) as compared
to the general population. This is presumably related to the contribution of
ADHD traits to executive function and a higher-than-typical rate of ADHD
symptomatology among the participants. (The low trait group was matched
to the high trait group in terms of ADHD scores.)
596 CHRIST, KANNE, AND REIERSEN
This document is copyrighted by the American Psychological Association or one of its allied publishers.
This article is intended solely for the personal use of the individual user and is not to be disseminated broadly.

higher functioning and more tolerant of a structured testing envi-
ronment, a broader range of neurocognitive assessment tools and
approaches may be applied to the study of this population than
would otherwise be feasible in research involving only individuals
with diagnosed ASD. Thus, unique insight may be gained by
studying these individuals.
As detailed above, the present findings are consistent with past
research on executive function, ADHD symptomatology, and au-
tism traits. A possible limitation of the present study, however,
relates to its reliance on self-report measures to assess personality
traits and executive functioning in participants. The potential for
response bias is presumably greater when utilizing report measures
(self, parent, and/or teacher) than when the examiner directly
observes or assesses the behavior him or herself. The present
pattern of results (i.e., ADHD and ASD traits contribute separately
to distinct aspects of executive function), however, is inconsistent
with the presence of a general response bias (e.g., individuals who
report aberrant behavior on one measure are more likely to report
difficulties/pathology on other measures). Regardless, in the future
we plan to expand our testing battery to include both report and
behavioral measures, the latter of which is less susceptible to
response bias. In addition, to the extent that report and behavioral
measures may capture different aspects of functioning (Toplak,
Bucciarelli, Jain, & Tannock, 2009), inclusion of both types of
measure may provide additional insight into the complex contri-
butions of ADHD and ASD traits to cognitive functioning.
In closing, the results of the current study are consistent with
past research linking ASD and executive difficulties. In addition,
while ADHD and ASD traits appeared to share a common influ-
ence, there was evidence of a unique contribution of each to the
executive control profile of individuals with subthreshold autism
traits. This finding underscores the importance of accounting for
ADHD symptomatology in studying ASD. In addition, the present
study demonstrates the value of studying individuals with sub-
threshold autism traits in that this line of research has the potential
to significantly advance our understanding of ASD.
References
Achenbach, T. (1991). Manual for the Child Behavior Checklist/4–18 and
1991 profile. Burlington, VT: Department of Psychiatry, University of
Vermont.
American Psychiatric Association. (2000). Diagnostic and statistical man-
ual of mental disorders (4th ed., text revision). Washington, DC: Author.
Barkley, R. A. (1997). Behavioral inhibition, sustained attention, and
executive functions: Constructing a unifying theory of ADHD. Psycho-
logical Bulletin, 121, 65–94.
Baron-Cohen, S., Wheelwright, S., Skinner, R., Martin, J., & Clubley, E.
(2001). The autism-spectrum quotient (AQ): evidence from Asperger
syndrome/high-functioning autism, males and females, scientists and
mathematicians. Journal of Autism and Developmental Disorders, 31,
5–17. doi: 10.1023/A:1005653411471
Bishop, D. V., Maybery, M., Maley, A., Wong, D., Hill, W., & Hallmayer, J.
(2004). Using self-report to identify the broad phenotype in parents of
children with autistic spectrum disorders: A study using the Autism-Spec-
trum Quotient. Journal of Child Psychology and Psychiatry and Allied
Disciplines, 45, 1431–1436. doi: 10.1111/j.1469-7610.2004.00325.x
Bradshaw, J. (2001). Developmental disorders of the frontostriatal system:
Neuropsychological, neuropsychiatric, and evolutionary perspectives.
Philadelphia: Psychology Press.
Bradshaw, J., & Sheppard, D. (2000). The neurodevelopmental frontos-
triatal disorders: Evolutionary adaptiveness and anomalous lateraliza-
tion. Brain and Language, 73, 297–320. doi: 10.1006/brln.2000.2308
Christ, S., Holt, D., White, D., & Green, L. (2007). Inhibitory control in
children with autism spectrum disorder. Journal of Autism and Devel-
opmental Disorders, 37, 1155–1165. doi: 10.1007/s10803-006-0259-y
Constantino, J. N., Davis, S. A., Todd, R. D., Schindler, M. K., Gross, M. M.,
Brophy, S. L.,...Reich, W. (2003). Validation of a brief quantitative
measure of autistic traits: Comparison of the social responsiveness scale
with the autism diagnostic interview-revised. Journal of Autism and Devel-
opmental Disorders, 33, 427–433. doi: 10.1023/A:1025014929212
Constantino, J. N., Gruber, C. P., Davis, S., Hayes, S., Passanante, N., &
Przybeck, T. (2004). The factor structure of autistic traits. Journal of
Child Psychology and Psychiatry and Allied Disciplines, 45, 719–726.
doi: 10.1111/j.1469-7610.2004.00266.x
Constantino, J. N., Hudziak, J. J., & Todd, R. D. (2003). Deficits in
reciprocal social behavior in male twins: Evidence for a genetically
independent domain of psychopathology. Journal of the American Acad-
emy of Child and Adolescent Psychiatry, 42, 458–467. doi: 10.1097/
01.CHI.0000046811.95464.21
Constantino, J. N., Przybeck, T., Friesen, D., & Todd, R. D. (2000).
Reciprocal social behavior in children with and without pervasive de-
velopmental disorders. Journal of Developmental and Behavioral Pedi-
atrics, 21, 2–11.
Constantino, J. N., & Todd, R. D. (2000). Genetic structure of reciprocal
social behavior. American Journal of Psychiatry, 157, 2043–2045. doi:
10.1176/appi.ajp.157.12.2043
Constantino, J. N., & Todd, R. D. (2003). Autistic traits in the general
population: A twin study. Archives of General Psychiatry, 60, 524–530.
doi: 10.1001/archpsyc.60.5.524
Gadow, K. D., DeVincent, C. J., & Pomeroy, J. (2006). ADHD symptom
subtypes in children with pervasive developmental disorder. Journal of
Autism and Developmental Disorders, 36, 271–283. doi: 10.1007/
s10803-005-0060-3
Geurts, H., Verte, S., Oosterlaan, J., Roeyers, H., & Sergeant, J. (2004).
How specific are executive functioning deficits in attention deficit hy-
peractivity disorder and autism? Journal of Child Psychology & Psy-
chiatry, 45, 836–854. doi: 10.1111/j.1469-7610.2004.00276.x
Gilotty, L., Kenworthy, L., Sirian, L., Black, D. O., & Wagner, A. E. (2002).
Adaptive skills and executive function in autism spectrum disorders. Child
Neuropsychology, 8, 241–248. doi: 10.1076/chin.8.4.241.13504
Gioia, G., Isquith, P., Guy, S., & Kenworthy, L. (2000). Behavior rating
inventory of executive function. Odessa, FL: Psychological Assessment
Resources.
Gioia, G., Isquith, P., Kenworthy, L., & Barton, R. (2002). Profiles of
everyday executive function in acquired and developmental disorders.
Child Neuropsychology, 8, 121–137. doi: 10.1076/chin.8.2.121.8727
Goldstein, S., & Schwebach, A. J. (2004). The comorbidity of Pervasive
Developmental Disorder and Attention Deficit Hyperactivity Disorder: Re-
sults of a retrospective chart review. Journal of Autism and Developmental
Disorders, 34, 329–339. doi: 10.1023/B:JADD.0000029554.46570.68
Hill, E. (2004). Evaluating the theory of executive dysfunction in autism.
Developmental Review, 24, 189–233.
Hughes, C., Leboyer, M., & Bouvard, M. (1997). Executive function in
parents of children with autism. Psychological Medicine, 27, 209–220.
doi: 10.1017/S0033291796004308
Hughes, C., Plumet, M., & Leboyer, M. (1999). Towards a cognitive
phenotype for autism: Increased prevalence of executive dysfunction
and superior spatial span amongst siblings of children with autism.
Journal of Child Psychology & Psychiatry, 40, 705–718. doi: 10.1017/
S0021963099004023
Jobe, L., & White, S. (2007). Loneliness, social relationships, and a
broader autism phenotype in college students. Personality and Individ-
ual Differences, 42, 1479–1489. doi: 10.1016/j.paid.2006.10.021
597SUBTHRESHOLD AUTISM TRAITS & EXECUTIVE DYSFUNCTION
This document is copyrighted by the American Psychological Association or one of its allied publishers.
This article is intended solely for the personal use of the individual user and is not to be disseminated broadly.

Kanne, S. M., Christ, S. E., & Reiersen, A. M. (2009). Psychiatric symp-
toms and psychosocial difficulties in young adults with autistic traits.
Journal of Autism and Developmental Disorders, 39, 827–833. doi:
10.1007/s10803-008-0688-x
Kenworthy, L., Yerys, B., Anthony, L., & Wallace, G. (2008). Understand-
ing executive control in autism spectrum disorders in the lab and in the
real world. Neuropsychology Review, 18, 320–338. doi: 10.1007/
s11065-008-9077-7
Kim, J., Szatmari, P., Bryson, S., Streiner, D., & Wilson, F. (2000). The prevalence
of anxiety and mood problems among children with autism and Asperger
syndrome. Autism, 4, 117–132. doi: 10.1177/1362361300004002002
Landa, R. J., Holman, K. C., & Garrett-Mayer, E. (2007). Social and
communication development in toddlers with early and later diagnosis of
autism spectrum disorders. Archives of General Psychiatry, 64, 853–
864.
Losh, M., & Piven, J. (2007). Social-cognition and the broad autism
phenotype: Identifying genetically meaningful phenotypes. Journal of
Child Psychology and Psychiatry and Allied Disciplines, 48, 105–112.
doi: 10.1111/j.1469-7610.2006.01594.x
Luna, B., Minshew, N., Garver, K., Lazar, N., Thulborn, K., Eddy, W., &
Sweeney, J. A. (2002). Neocortical system abnormalities in autism: An
fMRI study of spatial working memory. Neurology, 59, 834–840.
Ozonoff, S., Rogers, S. J., Farnham, J. M., & Pennington, B. F. (1993). Can
standard measures identify subclinical markers of autism? Journal of
Autism and Developmental Disorders, 23, 429–441.
Pennington, B. F., & Ozonoff, S. (1996). Executive functions and develop-
mental psychopathology. Journal of Child Psychology and Psychiatry and
Allied Disciplines, 37, 51–87. doi: 10.1111/j.1469-7610.1996.tb01380.x
Pine, E., Luby, J., Abbacchi, A., & Constantino, J. N. (2006). Quantitative
assessment of autistic symptomatology in preschoolers. Autism, 10,
344–352. doi: 10.1177/1362361306064434
Piven, J., & Palmer, P. (1997). Cognitive deficits in parents from multiple-
incidence autism families. Journal of Child Psychology and Psychiatry
and Allied Disciplines, 38, 1011–1021.
Piven, J., & Palmer, P. (1999). Psychiatric disorder and the broad autism
phenotype: Evidence from a family study of multiple-incidence autism
families. American Journal of Psychiatry, 156, 557–563.
Piven, J., Palmer, P., Jacobi, D., Childress, D., & Arndt, S. (1997). Broader
autism phenotype: Evidence from a family history study of multiple-
incidence autism families. American Journal of Psychiatry, 154, 185–
190.
Psychological Corporation. (1999). Wechsler Abbreviated Scale of Intelli-
gence. San Antonio, TX: Psychological Corporation.
Reiersen, A. M., Constantino, J. N., Grimmer, M., Martin, N. G., & Todd,
R. D. (2008). Evidence for shared genetic influences on self-reported
ADHD and autistic symptoms in young adult Australian twins. Twin Re-
search and Human Genetics, 11, 579–585. doi: 10.1375/twin.11.6.579
Reiersen, A. M., Constantino, J. N., & Todd, R. D. (2008). Co-occurrence
of motor problems and autistic symptoms in attention-deficit/hyperac-
tivity disorder. Journal of the American Academy of Child and Adoles-
cent Psychiatry, 47, 662–672. doi: 10.1097/CHI.0b013e31816bff88
Reiersen, A. M., Constantino, J. N., Volk, H. E., & Todd, R. D. (2007).
Autistic traits in a population-based ADHD twin sample. Journal of
Child Psychology and Psychiatry and Allied Disciplines, 48, 464–472.
doi: 10.1111/j.1469-7610.2006.01720.x
Reynolds, R., & Kamphaus, R. (2000). Behavior assessment system for
children–2nd Edition. Circle Pines, MN: AGS Publishing.
Ronald, A., Simonoff, E., Kuntsi, J., Asherson, P., & Plomin, R. (2008).
Evidence for overlapping genetic influences on autistic and ADHD
behaviours in a community twin sample. Journal of Child Psychology
and Psychiatry and Allied Disciplines, 49, 535–542. doi: 10.1111/j.
1469-7610.2007.01857.x
Roth, R., Isquith, P., & Gioia, G. (2005). BRIEF-A: Behavior Rating
Inventory of Executive Function-Adult Version. Lutz, FL: Psychological
Assessment Resources.
Russell, J. (1997). Autism as an executive disorder. Oxford: Oxford Uni-
versity Press.
Sturm, H., Fernell, E., & Gillberg, C. (2004). Autism spectrum disorders in
children with normal intellectual levels: Associated impairments and
subgroups. Developmental Medicine and Child Neurology, 46, 444–
447. doi: 10.1017/S0012162204000738
Stuss, D. (1992). Biological and psychological development of executive
functions. Brain and Cognition, 20, 8–23.
Szatmari, P., Jones, M. B., Tuff, L., Bartolucci, G., Fisman, S., & Ma-
honey, W. (1993). Lack of cognitive impairment in first-degree relatives
of children with pervasive developmental disorders. Journal of the
American Academy of Child and Adolescent Psychiatry, 32, 1264–1273.
Tantam, D. (2000). Psychological disorder in adolescents and adults with Asperger
syndrome. Autism, 4, 47–62. doi: 10.1177/1362361300004001004
Toplak, M. E., Bucciarelli, S. M., Jain, U., & Tannock, R. (2009). Exec-
utive functions: Performance-based measures and the behavior rating
inventory of executive function (BRIEF) in adolescents with attention
deficit/hyperactivity disorder (ADHD). Child Neuropsychology, 15, 53–
72. doi: 10.1080/09297040802070929
Willcutt, E. G., Doyle, A. E., Nigg, J. T., Faraone, S. V., & Pennington,
B. F. (2005). Validity of the executive function theory of attention-
deficit/hyperactivity disorder: A meta-analytic review. Biological Psy-
chiatry, 57, 1336–1346. doi: 10.1016/j.biopsych.2005.02.006
Wong, D., Maybery, M., Bishop, D. V., Maley, A., & Hallmayer, J. (2006).
Profiles of executive function in parents and siblings of individuals with
autism spectrum disorders. Genes, Brain and Behavior, 5, 561–576.
doi: 10.1111/j.1601-183X.2005.00199.x
Woodbury-Smith, M. R., Robinson, J., Wheelwright, S., & Baron-Cohen,
S. (2005). Screening adults for Asperger Syndrome using the AQ: A
preliminary study of its diagnostic validity in clinical practice. Journal
of Autism and Developmental Disorders, 35, 331–335. doi: 10.1007/
s10803-005-3300-7
Zandt, F., Prior, M., & Kyrios, M. (2009). Similarities and differences between
children and adolescents with autism spectrum disorder and those with
obsessive compulsive disorder: Executive functioning and repetitive behav-
iour. Autism, 13, 43–57. doi: 10.1177/1362361308097120
Received August 10, 2009
Revision received January 4, 2010
Accepted January 11, 2010 䡲
598 CHRIST, KANNE, AND REIERSEN
This document is copyrighted by the American Psychological Association or one of its allied publishers.
This article is intended solely for the personal use of the individual user and is not to be disseminated broadly.