Behaviour phenotype for Down's

BRITISH JOURNAL OF PSYCHIATRY (1998),
172, 85-89
Behaviour phenotype for Down's syndrome
RICHARD A. COLLACOTT,
and CATHERINE
Background
SALLY-ANN
For more than a century,
the idea of particular personality/
behavioural characteristics being
associated with people with Down's
syndrome has been explored, but with
inconclusive results.
Method
COOPER, DAVID BRANFORD
McGROTHER
The Disability Assessment
Schedule was used to ascertain the
behavioural profiles of 360 adults with
Down's syndrome and 1829 adults with
learning disabilities of other aetiologies,
who were the whole identified population
within a defined geographical area.
Since Langdon Down's original description
(1866), people with Down's syndrome have
historically been considered to possess
characteristic personality and behavioural
traits. However, although there have been
several studies in this area, it is unclear
whether a personality/behavioural
pheno
type specific to people with Down's syn
drome exists. In order to examine this
further, we examined the behavioural
characteristics of a substantial and unselected cohort of adults with Down's
syndrome, compared with the total ascer
tained population of individuals with learn
ing disabilities
resident in a defined
geographical region of the UK.
METHOD
subgroups aged < 35 years and aged > 35
Participants
years. Comparison was also made with
Individuals with learning disabilities were
identified via the Leicestershire Information
Coordination Centre (LICC). The LICC
was established during a process of active
case-finding, coordinated by the Depart
regards to cluster analysisfindings.
Results
Despite an equal ageand
developmental quotient, the Down's
syndrome group were lesslikely to
demonstrate maladaptive behaviours.The
behaviour characteristics of the adults
with Down's syndrome remained constant
in the younger and older age groups.
Cluster analysisdemonstrated adults with
Down's syndrome to have an increased
prevalence in cluster groupings with lower
rates of maladaptive behaviours.
Conclusions
This studyconfirms there
to be a behaviour phenotype among
adults with Down's syndrome.The reasons
for this (e.g. genetic/psychological/social)
require further research. Such research
may establish a better understanding of
the aetiologies of maladaptive behaviours
among people with learning disabilities in
general.
tiveness, untruthfulness, absconsion, exces
sive activity and excessive noise. For the
purposes of this study, such behaviours were
scored on a dichotomous scale depending on
whether the behaviour was present or
absent. The characteristics of the behaviour
of the total Leicestershire population of
individuals with learning disabilities has
been previously described (Smith et al,
1996).
Analyses
Comparison was made between the two
total groups and additionally for the
tion about the characteristics of the person
and numerous aspects of their behaviour
and abilities. The questions and their
ratings included the Disability Assessment
Schedule (DAS; Holmes et al, 1982). The
questionnaire was administered by staff
who had undertaken training which in
cluded interrater reliability, as advocated
by Holmes et al (1982).
Questions related to a wide range of
maladaptive behaviours and provided infor
mation concerning their frequency and
severity. These included aggression, anti
social behaviours, destructiveness, scattering
objects, attention seeking, disturbing others,
sexual delinquency, self-injury, uncoopera-
ment of Epidemiology and Public Health,
Leicester University. The ascertainment
rate (2.56 per 1000 total population)
compares favourably with that in other
regions of the UK (Farmer et al, 1993).
Individuals with Down's syndrome had
The first stage of this study was the
comparison of the prevalence of maladap
tive behaviours in individuals with and
without Down's syndrome. In view of the
universal prevalence of histopathological
changes of Alzheimer's disease in indivi
duals with Down's syndrome over the age
of 35 years, in the second stage of this study
the prevalence of maladaptive behaviour
was further studied in subgroups depending
on whether the age of 35 years had been
attained or not. In a third stage of this
study, comparison was made between the
Down's syndrome group and the control
previously been independently ascertained
through widespread search of National
Health Service records, social services and
private care homes (Collacott, 1992) in
addition to the LICC process.
group, with regards to cluster analysis
findings. An earlier study (Smith et al,
1996) developed a typology of maladaptive
behaviour in adults with learning disability
based on cluster analysis. The initial mal
adaptive behaviours were examined using
the 'k-means' programme. The k-means
Measures
cluster analysis requires
The LICC supports a programme of home
interviews using trained interviewers. The
programme aims to interview a key person
involved with the care of each adult with
learning disabilities registered with the
LICC once every five years. The first round
of interviews was completed in the summer
of 1994, providing information on 2277
adults. The questionnaire sought informa
number of clusters: the number of clusters
for further analysis was chosen on the basis
of the validity of the clusters ascertained by
clinical practice. Six behavioural clusters
had been identified which bore similarity to
those previously defined by Reid et al
(1978). These are outlined in the Appendix.
The prevalence of people falling into each
of the cluster categories was compared
a user-specified
85
COLLACOTT
ET
AL
between those with and those without
Down's syndrome.
13 behaviours examined, compared with
those without Down's syndrome. The low
er scores for the Down's syndrome group
RESULTS
were significantly different for 10 of the
behaviours. For those with Down's syn
Group characteristics
drome aged >35 years the prevalence of
maladaptive behaviours was lower for 12
of the 13 behaviours examined. However,
for only seven behaviours was the differ
ence in prevalence significant (Table 2).
There was no significant difference in
the prevalence of any of the 13 maladaptive
Behavioural records were completed for
2189 (96%) of 2277 adult individuals with
learning disabilities known to the LICC.
Among the 2189 individuals, 360 (16.44%)
had Down's syndrome, of whom 164
(45.56%) were aged <35 years and 196
(55.44%) were aged ^35 years. The mean
age of those with Down's syndrome was
37.14 years (95% CI 35.99-38.30) and
37.84 years (95% CI 37.15-38.53)
for
those without Down's syndrome. The mean
Table I
developmental quotient was 29.39 (95% CI
28.25-30.54) for those with Down's syn
between
those with
Down's
syndrome aged < 35 years and those who
were older. For individuals
without
Down's syndrome, the prevalence of nine
types of maladaptive
behaviour
was
significantly reduced in those who were
older group compared with those aged
< 35 years. The maladaptive behaviours in
non-Down's syndrome individual, the pre
valence of which did not change with age,
included aggression, antisocial behaviour,
sexual delinquency and untruthfulness.
Prevalence of maladaptive behaviours
Down's syndrome (n=360)
Maladaptive behaviour
drome and 30.33 (95% CI 29.67-30.99)
for those without Down's syndrome.
behaviours
Non-Down's syndrome (n=l829)
(31)***4.72(17)**8.89
AggressionAntisocial
(444)9.24(169)18.97(347)14.76
behaviourProperty
For the total group there were signifi
cant differences in the prevalence of
maladaptive behaviour between the two
groups (Table 1). People with Down's
(32)***9.72
destructionDisturbing
(35)*3.89(14)«12.22(44)***1.67(6)7.22
(270)8.80(161)27.67
nightScattering
others at
objectsAttention-seekingSexual
syndrome had lower rates of each of the
13 maladaptive behaviours examined, and
for 11 behaviours this lower prevalence
was significant.
(506)3.39
delinquencySelf-injuryUncooperativenessUntruthfulnessExcessive
(26)***25.39
(62)19.52(357)31.22(571)11.21
(95)6.94
(25)*3.33(12)***5.00(18)**9.17(33)***24.28
(205)16.62(304)10.66(195)16.73(306)
Age effects
activityAbsconsionExcessive
The second stage of the study showed that
for adults aged <35 years with Down's
noise8.61
syndrome, the prevalence of maladaptive
behaviours was again lower in each of the
Table 2
*P<0.05. **P<O.OI,«*P<O.OOI.
Prevalence of maladaptive behaviours for those aged < 35 years those aged
Maladaptive behaviour
35 years
Age ~^35 years
Age < 35 years
syndrome
(n=l64)
syndrome
(n=93l)
%(n)8.54(14)***4.27(7)9.15(15)***9.76(16)*2.44
X(n)25.56
AggressionAntisocial
syndrome
(n=l96)
(74)22.45
destructionDisturbing
(209)17.51
nightScattering
others at
objectsAttention-seekingSexual
(206)10.38(95)15.08(138)11.69(107)6
(17)*9.69(19)5.10(10)12.76
(163)10.85(101)29.54
(4)***11.59(19)***1.83(3)9.76(16)***25.00(41)**6.10(10)4.27
(275)2.69
delinquencySelf-injuryUncooperativenessUntruthfulnessExcessive
(n=9IS)
%(n)8.67(17)***5.10(10)*8.67 %(n)22.51
(238)7.95
behaviourProperty
syndrome
(55)25.25(231)4.04
1
(25)***1.53(3)5.10(10)***27.55
(25)23.31
(37)15.30(140)26.45
(217)35.34
(329)10.42(97)19.12(178)12.46(116)18.80(175)Down's
(54)7.65(15)2.55
(7)***4.88
activityAbsconsionExcessive
(8)**10.37(17)**Non-Down's
(79)14.34(131)versus
noise*P<0.05,
**P<O.OI,"*P<O.OOI,Down'snon-Down's
8«
syndrome
of same age group.
(242)11.80(108)13.77(126)8.63
(5)***5.10(1)8.16(16)*Non-Down's
Behavioural clusters
Age effect and behavioural clusters
populations, but also for the under 35-year-
The third stage of the study examined the
total group with Down's syndrome. The
Table 3 also shows the prevalence for each
cluster group for the adults with Down's
pattern of membership of behavioural
clusters was found to be significantly
different from that in those people with
out Down's syndrome (x2=69.73, d.f.=5,
syndrome and the adults with learning
disabilities of other aetiologies, dependent
upon whether they are aged < 35 years or
>35 years. For the younger group, a
significant difference was noted in the
number of people forming the membership
of each group, between those with and
without Down's syndrome. For those aged
olds and the two groups aged >35 years.
The difference was more marked in the
younger adults. Differences in the propor
tion of people in each of the previously
defined behaviour clusters were also found.
People with Down's syndrome were more
P < 0.001). In particular, clusters 1 and 2
consisted of 8.9 and 8.5%, respectively,
of the group without Down's syndrome,
but only 2.2 and 4.4%, respectively, of
the group with Down's syndrome. Clus
ters 1 and 2 include individuals with high
levels of aggressive and destructive behav
iours, including self-injury. These behav
ioural clusters also include
described as attention-seeking,
individuals
overactive,
noisy and uncooperative.
Within these
clusters high rates of autistic symptoms,
including difficulties with social inter
action, empathy, repetitive speech and
stereotypy are present. In addition, clus
ters 4 and 6 consisted of 15.1 and 6.2%,
respectively, of the group without Down's
of the six groups. No significant difference
is found for groups 2 and 4 (although the
proportion of people in both these groups is
higher in the non-Down's syndrome adults
than in the Down's syndrome adults).
Study design
includes individuals whose major behav
ioural difficulty was that of attentionseeking. Cluster 6 was characterised by
high rates of aggressive, destructive and
antisocial behaviours. On the other hand,
cluster 3 comprised only 10.0% of those
without Down's syndrome but over 17%
of those with Down's syndrome. Cluster 3
included a group generally considered to
be uncooperative but who demonstrated
few other maladaptive behaviours. Cluster
5 - those without significant behavioural
difficulties - comprised only 51.3% of
those without Down's syndrome, but over
65% of those with Down's syndrome
(Table 3).
syndrome who reach the age of 35 years.
However, the changes between the Down's
syndrome and control subjects in the older
versus younger age groups appear to be due
to changes in the behavioural profiles of
control subjects with age, rather than
changes in Down's syndrome subjects with
DISCUSSION
syndrome, but only 8.6 and 1.7% of the
group with Down's syndrome. Cluster 4
Table 3
>35 years, differences in the numbers in
each cluster group between those with and
without Down's syndrome are seen in four
likely to belong to clusters 3 and 5 than
were the control individuals. Differences
were found between both the two groups of
younger adults and the two groups aged
>35 years. However, the differences were
more marked for the younger adults.
The reason for splitting the groups for
comparison on the basis of age was the
presence of histopathological changes of
Alzheimer's disease in people with Down's
This study has the advantage of being a
large, population-based study. All adults
identified to have Down's syndrome and
identified to have learning disabilities of
other causes within a defined geographical
area were included. This includes indivi
duals living both in the community and in
National Health Service accommodation.
The identification of such subjects followed
a prolonged period of active case-finding.
The instrument used to rate behaviour with
the informant is robust, and has been
previously validated (Holmes et al, 1982).
Adults with Down's syndrome were
found to have lower prevalences of mal
adaptive behaviours compared with control
adults with learning disabilities of other
aetiologies. This was true for the two whole
age. The behavioural characteristics of the
adults with Down's syndrome remained
remarkably constant in the two age bands.
Comparison of findings with
previous studies
Langdon Down (1866) commented upon
'powers of imitation', 'mimicry' and a
"humerous and lively sense of the ridicu
lous", and in a later paper 'obstinacy' and
'amiability'
(Down, 1877). Fraser &
Mitchell (1876)
istics of being
good tempered
chievous', "but
also described character
'cheerful', "affectionate,
and easily amused", 'mis
it is very rare to find him
guilty of bad temper or any of the vices or
bad habits which characterise so many of
Membership of behavioural clusters
Cluster
Total population
Aged < 35 years
Down's syndrome Non-Down's syndrome
Down's syndrome Non-Down's syndrome
o/ /_\
o/ /_.\
/b (n)
1234562.22
Aged > 35 years
Tb(n)
Down's syndrome Non-Down's syndrome
o//\
Tb(n)
o//\
?b(n)
(8)***4.44(16)**17.22(62)***8.61
(5)***4.27
(163)8.47(155)10.00(183)15.15(277)51.29(938)6.18(113)3.05
o//\
Ä (n)
(60)6.42
(7)*17.07
(9)17.35
(58)9.18(83)14.27(129)56.96(515)6.53
(28)*7.32(12)**67.07(110)***1.22(2)*11.14(103)10.49(97)10.81
(34)***9.69(19)64.80(127)*2.04
(100)16.00(148)45.72
(31)***65.84(237)***1.67(6)***8.91
(423)5.84
(54)1.53(3)**4.59
*P<0.05, **P<O.OI, *"P<0.001,
(4)*6.64
(59)
versus non-Down's syndrome in same agegroup.
•
7
the ordinary defectives". Fraser & Mitchell
(1876) also commented on traits of mimi
cry and musicality. Brousseau oc Brainerd
(1928) studied 40 people with Down's
syndrome, and concluded them to be
good-natured, cheerful, affectionate and
docile, and seldom ill-tempered or destruc
tive. However, Rollins (1946) in his study
of 73 people with Down's syndrome, found
60% to have a history
behaviours, which included
haviours. Only 44% of the
conformed to the stereotype.
suggested that people with
of abnormal
antisocial be
present group
Engler (1949)
Down's syn
drome fell into three groups, only one of
which coincided with the stereotype. The
other two groups consisted of people who
were either dull and listless, or excessively
pugnacious and spiteful. Blaketer-Simmonds (1953) compared the case notes of
140 people with Down's syndrome with
100 people with learning disabilities of
other aetiologies. The two groups were
similar for most characteristics, and dif
fered only with regards to increased mischievousness,
solitariness, and reduced
docility among the Down's syndrome
group. He further studied 60 people with
Down's syndrome and 300 people with
learning disabilities of other aetiologies,
using an informant-rated questionnaire of
personality traits, and found no differences
between the two groups.
Moore et al (1968) studied 536 people
with Down's syndrome (average age 21
years) and matched controls. They were
less likely to show hyperactivity, aggressive,
destructive, self-injurious, restless or noisy
behaviours. A larger group of 2606 people
with Down's syndrome, with the same
mean age, also showed differences from
controls, with higher proportions of so
cially adaptive, socially competent behav
iour (Johnson & Abelson, 1969). Most
other studies of the personality and behav
iour of people with Down's syndrome have
focused exclusively on children (Bridges oc
Cicchetti, 1982; Gibbs & Thorpe, 1983;
Gath oc Gumley, 1986; Rodgers, 1987;
Pueschel et al, 1991), with conflicting
results.
Methodological differences from
previous studies
Several of the previous studies exploring
this area have used children as subjects.
Childhood is a time when personality is
shaped and develops, and so results from
findings of children cannot be extrapolated
88
to infer that the same is true for adults. This
highlights problems in those studies which
have grouped together both children and
adults. Of those studies which have exam
ined the characteristics of adults only,
conflicting results have been found with
regard to whether there is a characteristic
behaviour profile in Down's syndrome.
This may relate in part to the different
methodologies employed. Some studies did
not include a reference control group
(Brousseau ÖCBrainerd, 1928; Rollins,
1946), others used case notes as the source
of information or informant-rated ques
tionnaires (Blaketer-Simmonds, 1953). Of
the larger studies of adults which employed
the use of a control group, contrary results
were found. Blaketer-Simmonds
(1953)
found no differences between the Down's
syndrome and non-Down's
syndrome
groups, whereas behavioural differences
were found in two of the studies which
grouped children and adults together
(Moore et al, 1968; Johnson oc Abelson,
1969).
Despite this background of conflicting
results, the present results contribute
further to the concept of there being a
behaviour
phenotype
associated
with
Down's syndrome. The study gives some
support to the original comments of Fraser
Se Mitchell (1876) regarding the character
istics of people with Down's syndrome.
schizophrenia (Collacott et al, 1992). Over
the age of 35 years many people with
Down's syndrome have clinical dementia.
This may account for the fact that no
statistically significant difference is seen
between people aged <35 years compared
with those aged >35 years with Down's
syndrome, whereas among those without
Down's syndrome (fewer of whom will
have dementia) the prevalence of nine types
of maladaptive behaviours were signifi
cantly reduced in the older group.
ACKNOWLEDGEMENTS
The authors acknowledge the assistance of the Infor
mation Liaison Officers of the LICC in obtaining the
original data, and Mrs L McManus for interpreting
the original manuscript.
APPENDIX
Summary of cluster characteristics
Ouster /. A wide range of maladaptive behaviours.
More than half had aggressive and destructive
behaviour, including self-injury. Two-thirds were de
scribed as 'attention-seeking'. Most were excessively
active, noisy and uncooperative. Nearly half tended
to abscond. Associated behaviours included in
creased prevalence of continuous eating or drinking,
pica, hoarding rubbish, inappropriate sexual behav
iours, faecal smearing, spitting, swearing, tantrums
and self-induced vomiting. People in this cluster had
significantly more autistic symptoms than the total
population, were younger and of lower develop
Possible explanation
of results
There are many conceivable reasons why
people with Down's syndrome may have
reduced rates of maladaptive behaviours
compared with people with learning dis
abilities of other aetiologies. The answer
may lie at a genetic level: Down's syndrome
is associated with structural and functional
brain abnormalities (e.g. reduced levels of
serotonin). Differences in the age structure,
and range and central tendency of develop
mental quotient, were not found between
the Down's syndrome and non-Down's
syndrome groups, and so do not account
for differences found in the distribution and
prevalences of maladaptive behaviours.
Psychological and social factors may
alternatively or additionally contribute to
lower rates of maladaptive behaviours.
Previous research has demonstrated that
Down's syndrome is associated with a
psychiatric phenotype, including predispo
sition to dementia (Oliver oc Holland,
1986) and depression (Collacott et al,
1992), but a relative protection from
mental quotient, and a higher proportion
were
male. A significantly higher proportion of individuals
had epilepsy.
Cluster 2. Most individuals in this cluster had ag
gressive and destructive
behaviours, and 90%
showed self-injurious behaviour. They were unco
operative and half were excessively noisy. Unlike
cluster I. attention-seeking
behaviour, disturbing
others and absconsion were not frequent, and they
were not excessively active. Associated behaviours
included increased prevalence of continuous eating/
drinking, pica, inappropriate sexual behaviours, fae
cal smearing, swearing, tantrums and self-induced
vomiting. People in this group had significantly more
autistic symptoms than did the total population,
were younger and of lower developmental quotient
and a higher proportion were male. The prevalence
of epilepsy among people in this group was compar
able with that in the total study population.
Cluster 3. Members of this cluster had the charac
teristic of uncooperativeness, but few other mal
adaptive behaviours.
Difficulties
with social
interactions were more common than in the total
population, but there were no other associated mal
adaptive features. Age, developmental quotient,
gender ratio and seizure prevalence were similar to
those in the total population.
BEHAVIOUR
PHENOTYPE
FOR
DOWN'S
SYNDROME
Cluster 4. Membership of this cluster was defined
by the presence of attention-seeking behaviour, but
few other maladaptive behaviours. Autistic symp
CLINICAL
toms, age, developmental quotient, gender ratio
and seizure prevalence were similar to those in the
•Adults with Down's syndrome have a lower prevalence of maladaptive behaviours,
total population.
compared with adults with learning disabilities of other causes.
Cluster 5.
IMPLICATIONS
•Adults with Down's syndrome have a different
Membership of this cluster was charac
behavioural
profile compared with
terised by the very low prevalence of maladaptive
behaviours and autistic symptoms. Age. gender ratio
adults with learning disabilities of other causes.
and seizure prevalence were similar to those in the
total population, but the developmental quotient
•These findings help to provide insights into the aetiology of maladaptive behaviours
that might be explored
in future research.
was higher.
LIMITATIONS
Cluster 6. Behaviour characterised by high rates of
aggression, destructive and antisocial behaviour,
along with attention-seeking, uncooperative and un
truthful
•Maladaptive behaviours were recorded without
reference to psychiatric diagnoses.
•Shortage of previous research among adults with Down's syndrome with which to
behaviour. Associated behaviours included
higher rates of hoarding rubbish, inappropriate sex
make comparisons.
ual behaviours, faecal smearning, spitting, swearing
and, especially, temper outbursts. The prevalence of
autistic symptoms, gender ratio and seizure preva
lence were similar to those in the total population.
Members of this cluster were older and of higher
developmental quotient compared with the total
population.
RICHARD A. COLLACOTT. FRCPsych,Western Isles Health Board; SALLY-ANN COOPER. MRCPsych,
Rockingham Forest NHS Trust. Kettering, Northants;
CATHERINE McGROTHER, MFPHM, Department
DAVID BRANFORD. PhD. Frith Hospital. Leicester:
of Epidemiology and Public Health, University of Leicester
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