Comorbidity of autisticspectrum disorders inchildren with Downsyndrome

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 ofautistic spectrum disorders in a population of children withDown syndrome (DS). All children with DS within a definedpopulation of South Birmingham were identified. TheAsperger Syndrome Screening Questionnaire and the ChildAutism Rating Scale were completed and diagnosis madeaccording to ICD-10 criteria following interview andobservation. Thirty-three of 58 identified children completedthe measures, four of whom received a diagnosis of an autisticspectrum disorder. This is equivalent to a minimum comorbidrate of 7%. The questionnaire items concerning socialwithdrawal, restricted or repetitive interests, clumsiness, andunusual eye contact were associated with an autistic disorder.Of the remaining 29 participating children, 11 also displayedmarked obsessional and ritualistic behaviours. The comorbidoccurrence of autism and DS is at least 7%. It is importantthat these children are identified and receive appropriateeducation and support. A full assessment of social, language,and communication skills and behaviour is crucial,particularly in children with DS who appear different fromother children with DS. Potential mechanisms accounting forthis 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

adolescents with DS, within a particular geographical area,

with a prospective design using questionnaire and rating

methods, direct observation, and interview.

MethodSUBJECTS

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

70 000, 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.

ResultsSAMPLE 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

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. He dislikes changes in his environment intensely,

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 SyndromeScreening 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 autisticspectrum 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

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’ (ttest=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.

DiscussionAlthough 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

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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