1. Comorbidity of autistic
spectrum disorders in
children with Down
syndrome
Lindsey Kent*, Lecturer, Parkview Clinic, Moseley;
Joanne Evans, Senior Registrar, Oaklands Centre, Selly Oak;
Moli Paul, Senior Registrar;
Margo Sharp, Principal Speech Therapist; Language Unit;
Parkview Clinic; Birmingham, UK.
*Correspondence to first author at Parkview Centre, 60
Queensbridge Road, Moseley, Birmingham, B13 8QE, UK.
The aim of the study was to identify the comorbidity of
autistic spectrum disorders in a population of children with
Down syndrome (DS). All children with DS within a defined
population of South Birmingham were identified. The
Asperger Syndrome Screening Questionnaire and the Child
Autism Rating Scale were completed and diagnosis made
according to ICD-10 criteria following interview and
observation. Thirty-three of 58 identified children completed
the measures, four of whom received a diagnosis of an autistic
spectrum disorder. This is equivalent to a minimum comorbid
rate of 7%. The questionnaire items concerning social
withdrawal, restricted or repetitive interests, clumsiness, and
unusual eye contact were associated with an autistic disorder.
Of the remaining 29 participating children, 11 also displayed
marked obsessional and ritualistic behaviours. The comorbid
occurrence of autism and DS is at least 7%. It is important
that these children are identified and receive appropriate
education and support. A full assessment of social, language,
and communication skills and behaviour is crucial,
particularly in children with DS who appear different from
other children with DS. Potential mechanisms accounting for
this comorbidity are discussed.
Autism is a severely disabling condition with associated
social, communication, and behaviour impairments which
place extensive demands on parents, teachers, and society.
Its prevalence in the general population is estimated to be 1
per 1000 (Baron-Cohen et al. 1996) although the prevalence
of all autistic spectrum disorders has been estimated to be as
high as 9 per 1000 of the general population (Wing 1996).
The coexistence of autistic spectrum disorders with Down
syndrome (DS) has previously been reported as relatively
rare (Gath and Gumley 1986, Rutter and Schopler 1988).
However, an increasing number of reports in the literature
suggest that the two conditions may coexist more commonly
than previously reported.
Gillberg et al. (1986) in an epidemiological study of psy-
chiatric disorders in children with learning disabilities
reported one child to have classic Kanner’s-type autism from
a group of about 20 children with DS. In addition, three of
the children showed ‘psychotic behaviour’. The authors
highlight how these findings contradict the stereotype that
all children with DS are good natured and without psychi-
atric problems. Lund (1988) in an epidemiological study of a
population of adults with learning disabilities in Denmark,
diagnosed five from a sample of 44 with DS as having autism.
Turk (1992) reported the prevalence of autism in boys with
DS as 9%, general learning disability as 36%, and fragile X as
27%, and suggested that having trisomy 21 may be protective
against serious disturbances of conduct and social function-
ing. As this study does not include females by virtue of choos-
ing fragile X (uncommon in girls) as a condition to study, this
reported prevalence of autism in DS may be inaccurate
which may invalidate the conclusion of a conferred protec-
tive effect from trisomy 21. These prevalence figures are all
clearly influenced by the sample size, age range of sample,
and the instruments, informants, and diagnostic criteria
employed.
In addition, a number of case reports in the literature
describe the occurrence of autistic spectrum disorders in
people with DS (Wakabayashi 1979, Ghaziuddin et al. 1992,
Howlin et al. 1995, Prasher and Clarke 1996, Kent et al. 1998).
The existing literature suggests that there may be a higher
rate of autism in DS than that expected by chance. The popu-
lation prevalence of DS was predicted to increase up to the
year 2000 as a result of rising maternal age (Nicholson and
Alberman 1992). A subsequent study by the same group
(Alberman et al. 1995) revealed that despite an increase in
the number of overall genetic diagnoses from all pregnan-
cies, the number of overall births of children with DS in
England and Wales fell between 1989 and 1993 from 1.1 to
0.9 per 1000 total live births as a result of an increased termi-
nation rate. If DS and autism were independent, the rate of
cooccurrence expected by chance would be approximately 1
per million of the general childhood population, assuming
the more recent prevalence of DS. Similarly, assuming there
is no association between the two clinical groups, the fact
that they already possess one diagnosis should not influence
the possibility of them having a further diagnosis, so the
prevalence of autism in DS would be expected to be 1 per
1000 (possibly rising to as high as 9 per 1000 if all autistic
spectrum disorders were considered) and the prevalence of
DS in autism would equally be 1 per 1000.
The following study aims to investigate the comorbidity of
autistic spectrum disorders in a population of children and
Developmental Medicine & Child Neurology 1999, 41: 153–158 153

2. adolescents with DS, within a particular geographical area,
with a prospective design using questionnaire and rating
methods, direct observation, and interview.
Method
SUBJECTS
All children with DS between the age of 2 and 16 years, resi-
dent within a geographical area of the West Midlands with a
total population within this age group of approximately
70000, were identified. To minimize the risk of not identify-
ing any children, three routes were used. All special-school
and mainstream-school nurses within the geographical area
identified children within their school with DS, as did the
three child-development clinics in the area. In addition, the
local branch of the DS Association identified all their mem-
bers within the specified age group within that area. Letters
were sent inviting all parents to participate in this study.
Fifty-eight children were identified through these three
routes. Assuming a prevalence of 1 per 1000 live births with
DS, the numbers were approximately in keeping with infor-
mation from the Office of Population Censuses and Surveys
Data for the geographical area concerned. Although a region-
al register for DS births does not exist, figures from the
Regional Genetic Laboratory confirmed our estimate of 58
cases to be a realistic figure. We are, therefore, confident that
we have managed to identify most, if not all, children with DS
who met our criteria within this population.
PROCEDURE
Following identification and consent, parents completed the
Aspergers Syndrome Screening Questionnaire (ASSQ)
(Ehlers and Gillberg 1993) which is a 27-item screening
questionnaire designed for use by parents and teachers to
screen for social deficits associated with autistic spectrum
disorders. Each item refers to a specific behavioural charac-
teristic which, in turn, is rated on a 3-point scale (rating 0 to
2). The range of possible scores is thus 0 (no disorder) to 54.
The interrater and test–retest reliability and validity have
been reported and ROC Curve analysis has demonstrated the
optimum cut-off point, for sensitivity and specificity purpos-
es, in a community sample, to be 19 when rated by parents
(Ehlers and Gillberg 1993, see Ehlers 1996).
Each parent and child was interviewed at home. The
Childhood Autism Rating Scale (CARS) (Schopler et al.
1986) was completed at interview. It is based on behavioural
observation and/or interview. It covers 14 domains generally
affected by severe problems in autism plus an overall catego-
ry of ‘impression of autism’. Each possible area is rated on a
4-point scale (rating 1 to 4) with total scores less than 29
being considered as indicative of ‘non-autism’, scores
between 30 and 36 indicative of ‘mild to moderate autism’,
and above 36 as ‘severe autism’. The CARS should not be
used as the only instrument for deciding on a diagnosis of
autism but it is useful as a guide to the severity of the syn-
drome, particularly in children who have a learning disabili-
ty in addition to autism (Gillberg et al. 1996). If a child
fulfilled diagnostic criteria for an autistic spectrum disorder,
they were observed at school and then interviewed and
observed by a principal speech therapist from the Regional
Language Unit (MS). Each child was diagnosed according to
the ICD-10 (WHO 1992) criteria for autism and level of
learning disability.
Results
SAMPLE CHARACTERISTICS
Of the 33 children who completed the full protocol, there
were 18 males and fifteen females. The age range was 2 to 15
years (mean 7.2 years). Two children attended mainstream
schools, the remainder attended special schools or nurs-
eries. The mean ASSQ score was 11 (range 0 to 28) with six
children scoring above the cut-off point of 18. The mean
CARS score was 23 (SD 6.7, range 15 to 46) with five children
scoring above the cut-off of 30. There was no difference in
scores by age or sex. The overall correlation between the
ASSQ and the CARS was good (r=0.40, P<0.05).The report-
ed frequency of ASSQ items in the whole sample of children
with DS are demonstrated in Table I with at least 50% of the
sample reporting the items: ‘wishes to be sociable but fails to
make relationships with friends’, ‘lacks best friend’, ‘lacks
common sense’, and ‘has clumsy, awkward movements’.
AUTISTIC SPECTRUM DISORDERS
Of the 33 children assessed, four had difficulties which
placed them on the autistic spectrum according to ICD-10
criteria: three children fulfilled criteria for atypical autism
and one child for childhood autism. These children are
described below. If the total number of children identified
(58) is employed as the denominator, a minimum comorbid
rate of 7% is produced. In addition, a further two children
also had pragmatic language difficulties with some obses-
sional behaviours but did not fulfil diagnostic criteria for an
autistic disorder.
The mean ASSQ score was 18 in the group with autism and
10 in the non-autistic group. The mean CARS score was 36 in
the group with autism and 21 in the non-autistic group. Only
one child in the group with autism scored above the cut-off
point on the ASSQ but all scored above the cut-off point on
the CARS. The level of learning disability was similar in both
groups. The ASSQ items which correlated significantly with
an eventual ICD-10 diagnosis of an autistic spectrum disor-
der in this population are shown in Table II.
Forward stepwise logistic regression was employed to
identify the ASSQ items which best predicted a diagnosis of
an autistic spectrum disorder in this population of children
with DS. The item ‘lives somewhat in a world of his own with
restricted idiosyncratic intellectual interests’ was the best
predictor (r2=0.9, B=–2.7, P<0.05).
Linear regression was also employed to identify which
ASSQ items best predicted the severity of the autistic disor-
der as assessed by the CARS. Four items: ‘clumsy, ill-coordi-
nated movements’, ‘lives in a world of his own with restricted
idiosyncratic interests’, ‘invents idiosyncratic words and
expressions’, and ‘has a deviant style of gaze’ were the best
predictors of severity (r2=0.8, and B=5.7, P<0.005; B=3.9,
P<0.001; B=4.4, P<0.001; B=–5.8, P=0.001 respectively).
The four children diagnosed as having an autistic spec-
trum disorder are described briefly below.
SUBJECT A
Subject A is a 6-year-old boy with DS (trisomy 21) and a mild
to moderate learning disability who had an uneventful birth
after a straightforward pregnancy. He demonstrates a num-
ber of areas of concern: he did not babble as a toddler, has
poor eye contact, does not gesture, and prefers his own
company. He does not initiate or demonstrate imaginative
154 Developmental Medicine & Child Neurology 1999, 41: 153–158

3. or symbolic play and displays a number of repetitive actions
and rituals including lining up objects. In his language
usage, he shows pronominal reversal, echolalia, inappropri-
ate remarks, literal understanding, and has difficulty follow-
ing rules. He is, however, particularly able with numbers
and has an excellent rote memory. He lacks empathy and
understanding of others’ emotions. He dresses and feeds
himself, helps with simple chores around the house and
with the care of his younger sibling. There is a marked dis-
crepancy in his social and language development compared
with other children with similar levels of learning disability,
with or without DS, and he fulfils ICD-10 criteria for atypical
autism. His ASSQ score was 17 and CARS score was 33.
SUBJECT B
Subject B is a 9-year-old girl with a moderate learning dis-
ability. Her delivery was uneventful after an uncomplicated
pregnancy. She was noted to have marked difficulties in
social interaction. She tends to live in a world of her own,
plays alongside rather than with other children, and rarely
seeks company unless for somewhat egocentric reasons.
Her play is repetitive and lacks imagination, she has poor
eye contact, limited use of gesture, and has marked
echolalia. She accumulates facts on many subjects although
she does not understand their meaning, and has a number
of routines and rituals including having to follow certain
routes such as sit in certain chairs, and eat certain food. She
is extremely preoccupied with videos which she watches
repetitively. Her social and language development are not
in keeping with her general level of learning disability. She
fulfils diagnostic criteria for atypical autism. Her ASSQ
score was 15 and her CARS score was 36.
SUBJECT C
Subject C is a 7-year-old boy with DS (translocation type)
and a moderate learning disability whose parents had
repeatedly expressed concerns about his social and lan-
guage development which they perceived as being different
to other children with DS and a similar level of learning dis-
ability. His mother had an uneventful delivery and pregnan-
cy. Our subject had motor milestone development within
normal limits. Concerns about his hearing were expressed
because he appeared to ignore people, but hearing tests
were normal. His first words were around 18 months and
phrases around 36 months of age. His understanding is
extremely literal, he has some odd speech patterns and fails
to adjust to different social contexts, sometimes repeating
phrases he has heard elsewhere without understanding
their meaning.
The subject has always had difficulty making friends,
despite appearing sociable. Indeed, on observation he did not
make any attempt to engage or show interest in others but
would play alongside them, giving the impression of sociabili-
ty. His parents remarked that he had to be taught how to play
and he continues to play repetitively and rigidly, with little
imagination.Hedislikeschangesinhisenvironmentintensely,
no matter how trivial, and has a number of meal and bedtime
rituals. He is able to remember hours of dialogue and scenes
from videos and sometimes has difficulty completing simple
daily tasks as a result of his repetitive and ritualistic behav-
iours. He fulfils the ICD-10 criteria for atypical autism. His
ASSQ score was 23 and his CARS score was 31.
SUBJECT D
Subject D is a 6-year-old girl with DS and a moderate/severe
learning disability. Her parents expressed concerns that she
preferred her own company, never requested anything in any
manner, and became unusually distressed with changes in
her daily routines. She was born after an uneventful pregnan-
cy and birth, and had a septal defect corrected at 2 months of
age. There was a delay in her motor milestones: she began
walking aged 3 years 6 months. She did not babble, her first
Autistic Spectrum Disorders in Children with Down Syndrome Lindsey Kent et al. 155
Table I: Parental reported frequency of Asperger Syndrome
Screening Questionnaire items (N=33)
ASSQ item No Somewhat Yes
Old fashioned/precocious 29 2 1
Regarded as an eccentric professor 29 3 1
by other children
Lives in world of own with restricted 17 13 3
idiosyncratic interests
Good rote memory but does not 22 7 3
understand meaning
Literal understanding of ambiguous and 22 4 5
metaphorical language
Deviant style of communication 28 4 1
Invents idiosyncratic words or expressions 28 2 1
Different voice or speech 18 13 2
Expresses sounds involuntarily 26 2 4
Surprisingly good at some things 21 3 8
and bad at others
Fails to adjust language to social contexts 21 10 2
Lacks empathy 25 5 3
Makes naïve and embarrassing remarks 25 4 3
Deviant style of gaze 29 2 1
Wishes to be sociable but fails to make 16 13 4
friends with peers
Can be with other children but only 20 9 4
on their own terms
Lacks best friend 11 10 11
Lacks common sense 13 10 10
No idea of cooperating in a team/ 19 9 5
scores ‘own’ goals
Clumsy, ill-coordinated movements 12 12 9
Involuntary face or body movements 28 3 2
Difficulties completing simple activities 28 4 1
because of compulsory repetitive
actions or thoughts
Special routines: insists on no change 19 12 2
Idiosyncratic attachment to objects 26 7 0
Bullied by other children 30 3 0
Markedly unusual facial expression 27 5 1
Markedly unusual posture 26 6 1
Table II: ASSQ items significantly correlating with an autistic
spectrum diagnosis (N=33)
ASSQ item r value P value
Clumsy, ill-coordinated movements or gestures 0.4 <0.05
Compulsory repetitive activities 0.5 <0.01
Lives in world of own with restricted 0.5 <0.005
idiosyncratic interests

4. words were at 4 years of age, she neither gestures nor points,
and her parents often have to guess what she wants. Although
she does have some Makaton signs, she rarely uses them. She
demonstrates poor eye contact, little imaginative or symbolic
play, and tends to interrupt, although she is learning to take
turns.
Her motor movements are ill-coordinated; she toe walks,
and demonstrates other motor stereotypies such as hand flap-
ping and waving. In strange situations she will wander off. She
has no awareness of danger but can differentiate between
familiar and unfamiliar people. Her resistance to change is
marked and she demonstrates some inappropriate and ritual-
istic behaviours, for example, looking inside strangers’
mouths. Compared with her general level of learning disability
and other children with DS with similar levels of functioning,
there is a discrepancy in her social, language, and communica-
tion development. She fulfils ICD-10 criteria for childhood
autism. Her ASSQ score was 16 and her CARS score was 46.
OBSESSIONAL AND RITUALISTIC BEHAVIOURS
Of the 29 children who did not possess an autistic spectrum
disorder, eleven (seven males and four females) were noted to
have various obsessive–compulsive behaviours (OCB) which
had often provoked a query of an autistic diagnosis in the
child. Those with OCB were more likely to be older than those
without OCB (t test=3.72, P<0.005).The mean ASSQ score of
16 in this group was significantly higher than the 18 children
without OCB who had a mean score of 6 (t test=4.39,
P=0.001), but was not significantly different from that of the
mean score of 18 reported in the four children with autism.
The two ASSQ items which were scored significantly high-
er in the DS and OCB group than in the DS only group were:
‘lives in a world of his own with restricted interests’ (t
test=4.3, P<0.001) and ‘has special routines: insists on no
change’ (t test=4.3, P<0.001). Due to the small numbers of
children, analysis comparing items between those with
autism and those with OCB is not feasible.
Discussion
Although the sample for this study was relatively small, a
number of important findings have emerged. The estimated
minimum prevalence rate of 7% (four from 58 identified chil-
dren) for the coexistence of an autistic spectrum disorder
and DS is in keeping with the existing literature, suggesting a
prevalence of 1 to 11% (Gath and Gumley 1986, Lund 1988,
Collacott et al. 1992, Ghaziuddin et al. 1992). It is possible
that some of the non-responders may also have had autistic
spectrum disorders which would increase this prevalence as
this is the minimum possible prevalence. However, it is
equally likely that the non-responders did not have autistic
behaviours and perhaps thought that it would not be worth-
while participating. Unfortunately, the methodology
employed in this study prevents us from contacting the non-
responders as they were contacted by intermediaries on our
behalf to preserve confidentiality for ethical reasons. We are
aware that at least nine of the non-responder children are
attending mainstream schools where they are well integrat-
ed, mixing and performing well socially, and most do not
have additional special educational needs. This suggests that
these children do not possess significant autistic spectrum
disorders which would interfere with their educational and
social functioning.
The equal sex ratio of autistic disorders presented is
unusual. The majority of individuals who have been report-
ed as comorbid for autism and DS have been male (see
Prasher and Clarke 1996), although this may reflect underre-
porting in females where perhaps professionals expect even
less to diagnose autism. Our sex ratio finding may be due to
chance in a small sample but may also provide some indica-
tions for possible aetiological mechanisms.
None of the identified subjects in this series had a diagno-
sis of autism before the study, although it had been suggested
to professionals by the parents in three of the four subjects,
that their children were different compared with other chil-
dren with DS and comparable levels of learning disability.
This may be as a result of bias due to the very strong stereo-
type of DS individuals being sociable, good humoured, and
friendly. This stereotype may be unhelpful as it may bias pro-
fessionals in their assessment of these children so that behav-
iours, which may in fact be as a result of autism, are
attributed to the chromosomal abnormality or learning dis-
ability which may result in a full assessment of social skills
not being performed. A number of reports have demonstrat-
ed that not all individuals with DS have these personality
traits (Gibson 1978, Gillberg et al. 1986).
This bias may also be evident in parental reporting of
behaviours. Employing the ASSQ, a parent-rated question-
naire measure, only one of the four children with autism
scored over the cut-off point compared with the CARS, an
interview/observer measure, which successfully detected all
four children. This may be because parents are underreport-
ing the more ‘social’ deficit items on the ASSQ because they
do not expect their children with DS to have social deficits. It
may also be compounded by the ASSQ instrument which
tends to detect the features of more high-functioning indi-
viduals than those with moderate learning disabilities
(Ehlers 1996). A number of children who did not have autism
scored above the ASSQ cut-off point. This appears to be part-
ly as a result of the high scoring of items such as ‘clumsy, ill-
coordinated’ and ‘different voice or speech’, but it also
appears to be as a result of the high incidence of reported
restricted activities and routines in this group, both of which
may have inflated the total scores in this particular group of
children (however, it is important to note that the ‘stubborn
and resistant’ personality stereotype also used to describe
people with DS may also have influenced parental report-
ing). This is supported by the finding that only one child,
who did not have autism, scored over the cut-off point on the
CARS which makes proportionately less reference to repeti-
tive, ritualized, obsessional behaviours.
The item ‘clumsy and ill-coordinated’ was a significant pre-
dictor of severity of the autistic disorder, as rated by the CARS,
in addition to ‘lives in a world of his own with restricted idio-
syncratic interests’, ‘invents idiosyncratic words’, and
‘deviant style of gaze’. These four items which are, arguably,
relatively free of stereotyped bias, in addition to the item
‘repetitive activities’ (which correlated significantly with an
autistic diagnosis, although not a significant predictor) may
provide a clinically useful ‘screen’ in children with DS who
may be suspected of having an autistic spectrum disorder. In
the ASSQ validation studies, using a community sample, the
items: ‘has a different voice’, ‘good rote memory’, and ‘has a
literal understanding’ were the best predictors of a positive
finding (Ehlers 1996). These are clearly different from the
156 Developmental Medicine & Child Neurology 1999, 41: 153–158

5. best predictors in this study partly as a result of the different
sample and the ASSQ tending to detect higher-functioning
individuals. However, this also suggests that the presentation
of children with DS and autism may be different from that
which professionals expect to find, based on their previous
experience of diagnosing autism in children without.
As mentioned above, the other popular stereotype of DS
involves the stubborn, resistant to change, obsessional per-
sonality traits. If these behaviours are present, this may result
in a diagnosis of autism not being considered because pro-
fessionals and parents may expect children with DS to pos-
sess these behaviours as a matter of routine, in addition to
the sociable personality traits; further investigations for
other potential deficits may not be considered. However, in
the children in this sample who did not have autism, only 11
of the 29 showed these behaviours. The item ‘lives in a world
of his own with restricted interests’ was scored significantly
higher in the group with DS and OCB than the DS-only group
and was also a significant predictor of an autistic spectrum
disorder in the whole sample. This, therefore, emphasizes
the point that some of the obsessional traits which may be
seen in individuals with DS may be related to an autistic dis-
order and should not be ignored. In the children with DS and
OCB alone, and not autism, the social and language difficul-
ties associated with autism are not evident.
The problem of distinguishing between autistic-type
behaviours and essentially similar behaviours associated
with a learning disability may contribute to the difficulty in
diagnosis. The findings from this study highlight the point
that interview/observer-based methods, certainly in this
group, with standardized diagnostic assessments are likely
to be better diagnostic tools than questionnaires alone.
It is becoming increasingly apparent that a number of con-
ditions may be associated with comorbid autism, regardless
of other factors such as a positive family history for autistic
spectrum disorders. This is likely to be partly due to the
increasingly sophisticated recognition of autistic symptoms
generally, although Gillberg et al. (1991), in a study examin-
ing the prevalence in an area of western Sweden over 10
years, reported that the increase was also as a result of new
subjects with autistic symptoms born to immigrant parents.
In addition, many of the symptoms and behaviours in indi-
viduals with other conditions, including DS, have previously
been attributed to factors such as general cognitive delays
and chromosomal and other genetic abnormalities, despite
the fact that their behaviour and communication may differ
from other individuals with the same condition, with similar
levels of learning disability.
There are a number of possible mechanisms by which
comorbidity with autism may arise. A number of chromoso-
mal abnormalities have previously been reported in autism,
including fragile X, other sex chromosome abnormalities,
and partial tetrasomy 15 among others (Gillberg 1995),
although the nature of these associations remains unclear.
There are a number of studies suggesting that obstetric com-
plications may have an aetiological role in autism (Tsai
1987). The obstetric data on children with chromosomal and
genetic disorders suggest that fetal maldevelopment arising
from these disorders may, in fact, give rise to obstetric com-
plications (Bolton et al. 1994), although all four children
with autism in this sample had uncomplicated deliveries. In
addition, Lund (1988) suggested that different organic prob-
lems (e.g. heart defects) and congenital or early-acquired
brain defects may be responsible for the development of
autistic disorders in some individuals, either as a direct result
of a chromosome abnormality or indirectly because of an
increased vulnerability to anoxia, infection, or other harmful
effects during the intrauterine or neonatal period. Autism
associated with obstetric difficulties and/or fetal maldevelop-
ment as a result of a chromosomal abnormality, such as tri-
somy 21, may be a reason for the equal sex incidence
reported in this study.
One of the clear phenomenological overlaps between
autism and some of the conditions with which it may be
comorbid is the presence of OCB, for example, Tourette syn-
drome, a particular subtype of anorexia nervosa (Gillberg
1995) and, as demonstrated in this study, DS. Obsessive–com-
pulsive disorder (OCD) in adults with DS has been reported
(O’Dwyer et al. 1992, Prasher and Day 1995) and 15 of the 33
subjects in this study had OCB, including the children with
autism. However, there are differences in the actual obses-
sive–compulsive phenomenology between those described
in this sample of children with DS i.e. repetitive behaviours,
and those more commonly found in OCDs which tend to be
related to checking, counting, and cleanliness behaviours.
Similarly, McDougle et al. (1995) report the same differences
in phenomenology between OCD and autism with individu-
als with autism more likely to demonstrate repetitive, hoard-
ing, and ordering behaviours. These behaviours appear to be
of a perseverative quality, perhaps reflecting the known
frontal-lobe dysfunction which has been demonstrated in
both DS and autism by various disciplines including neu-
ropsychology (Ozonoff et al. 1991, McEvoy et al. 1993) and
neuroimaging (Bahado-Singh et al. 1992, Wang et al. 1992,
Zilbovicius et al. 1995).
In summary, this study has identified a minimum preva-
lence rate of autism in DS of 7%, which is higher than that
expected by chance alone. It is important that professionals
distance themselves from the strong stereotype of the
‘Down-syndrome personality’ which may bias assessment.
Both professionals and parents need to have access to infor-
mation about other conditions which may sometimes be
associated with DS, such as autism. This would enable earlier
diagnosis and ensure provision of appropriate advice and
education, which is likely to be different from that for indi-
viduals with DS alone.
Accepted for publication 21st August 1998.
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