Early learning and adaptive behaviour in toddlers with Down syndrome: Evidence for an
emerging behavioural phenotype?
Deborah Fidler, Susan Hepburn and Sally Rogers
Background: Though the Down syndrome behavioural phenotype has been described as
involving relative strengths in visuo-spatial processing and sociability, and relative
weaknesses in verbal skills and motor planning, the early emergence of this phenotypic
pattern of strengths and weaknesses has not yet been fully explored. Method: In this study,
we compared the performance of eighteen 2 to 3-year-olds with Down syndrome to an MA-matched
comparison group of nineteen 2 to 3-year-olds with mixed developmental disabilities, and an
MA-matched comparison group of 24 children with typical development on two developmental
measures: the Mullen Scales of Early Learning and the Vineland Adaptive Behaviour Scales.
Results: While the specificity of the Down syndrome profile was (for the most part) not yet
evident, results showed that toddlers with Down syndrome in this study did show emerging
areas of relative strength and weakness similar to that which has been described in older
children and young adults with Down syndrome. This pattern included relatively stronger
social skills, weaker expressive language, and poor motor coordination. When this pattern of
strengths and weaknesses was compared to the developmental profiles of the two comparison
groups, socialisation strengths differentiated the Down syndrome group from the mixed
developmental disabilities group.
Fidler DJ, Hepburn S, Rogers S. Early learning and adaptive behaviour in toddlers with Down syndrome: Evidence for an
emerging behavioural phenotype?. Down Syndrome Research and Practice. 2006;9(3);37-44.
There is a new wealth of evidence suggesting that certain genetic disorders are associated
with specific behavioural profiles, or 'behavioural phenotypes' (Dykens, 1995). Behavioural
phenotypes in genetic syndromes are defined probabilistically. Thus, groups with a certain
syndrome may be more likely to show one or more characteristic behaviours than other person
with developmental disabilities, but not every child with a specific syndrome necessarily
shows any etiology-specific behaviour (Dykens,
1995 Hodapp, 1997). This connection between
genetic condition and behavioural profile has the potential to revolutionise interventions
for individuals with developmental disabilities (Fidler, Hodapp & Dykens, 2002;
Lawson & Hodapp, 2003; Hodapp & Fidler, 1999).
In comparison with other genetic syndromes, a relatively large amount of research attention
has been devoted to describing outcomes associated with Down syndrome (Dykens, Hodapp &
Finucane, 2000). Down syndrome is the most common genetic (chromosomal) disorder, occurring
in from 1 in 700 to 1 in 1000 live births (Steele, 1996;
Stoll, Alembik, Dott & Roth, 1990;
Hassold and Jacobs, 1984). In 95% of cases, Down syndrome is caused by an extra chromosome
Much of the focus of research on cognition in Down syndrome has been placed on deficits in
verbal processing (Byrne, Buckley, MacDonald & Bird, 1995;
Hesketh & Chapman, 1998;
1998). In addition, studies have found relative strengths in visuo-spatial processing in
this population, and many individuals with Down syndrome have a profile of stronger
visuo-spatial than verbal processing skills (Jarrold, Baddeley & Hewes, 1999;
Klein & Mervis, 1999; Wang & Bellugi, 1994).
Many individuals with Down syndrome have severe language delays (Sigman & Ruskin, 1999).
Part of the Down syndrome language phenotype includes a discrepancy between expressive and
receptive language capabilities, including large deficits in vocabulary size relative to
mental age (Miller, 1992). Children with Down syndrome also show particular deficits in the
development of grammar, and many individuals with Down syndrome do not progress beyond the
early stages of morphological and syntactic development (Fowler, 1990).
Miller and Leddy
(1999) reported that the majority of children with Down syndrome experience a prolonged
period of unintelligible speech, often until age 5 or 6.
Despite their language deficits, many children with Down syndrome show strengths in social
functioning (Gibbs & Thorpe, 1983;
Rodgers, 1987; Wishart & Johnston, 1990). Children with
Down syndrome may also use relative strengths in social skills to compensate for other
weaker domains of functioning. In one study, young children with Down syndrome not only
showed more looks to the experimenter during a difficult task, but they also showed more
off-task 'party pieces' that engaged the experimenter socially (Pitcairn & Wishart, 1994).
Individuals with Down syndrome may also show relative competence in forming relationships
with others (Freeman & Kasari, 2002).
Another aspect of the Down syndrome behavioural phenotype involves difficulties with motor
skills and motor planning (Jobling, 1999;
Jobling, 1998; Mon-Williams et al., 2001).
(1998) found that children with Down syndrome show delays in the development of aspects of
gross motor and fine motor skills, though aspects of motor development were found to be
CA-appropriate. Similar relative weaknesses have been demonstrated in motor planning, or
praxis (Mon-Williams, et al., 2001).
While there is a growing body of knowledge regarding the Down syndrome behavioural
phenotype, much of what is known is based on research involving older children, adolescents,
and adults with Down syndrome (Haxby, 1989;
Jobling, 1998; Varnhagen, Das & Varnhagen, 1987;
Vicari, Carlesimo & Caltagirone, 1995;
Wang & Bellugi, 1994). By studying only older
children and adults, researchers may have a false impression that phenotypic outcomes are
static in nature, and that areas of relative strength and weakness are present from the
earliest stages of development. Yet, Nadel (1995) notes that most measures of brain
development and cognitive functioning are in the normal range during the first few months of
infancy in Down syndrome. If this is so, then the emergence of the Down syndrome phenotype
during early development may be of great importance to early interventionists. What
precipitates the evolution of the phenotypic profile associated with Down syndrome? And, is
there a way to strengthen development of areas that are expected to develop more slowly, and
thus prevent relative developmental weaknesses downstream?
In addition, most behavioural phenotype research focuses on one dimension of development in
isolation (i.e. working memory, praxis, joint attention). While detailed descriptions of a
specific domain of functioning are important, it may also be informative to explore how many
areas develop together – for example, to show whether cross-domain areas of relative
strength and weakness become more pronounced over time. Such findings may inform
interventions that take into account the whole child, not simply one aspect of the child
that may be of particular interest.
Two questions will be addressed in this study. First, are developmental profiles in toddlers
with Down syndrome specific to Down syndrome? This question will be addressed with
between-group analyses. And second, are distinct areas of strength and weakness in
functioning already present in early childhood? This question will be addressed using
within-Down syndrome analyses. In order to answer these questions, we will analyse the
performance of 2 to 3-year-olds with Down syndrome on the
Mullen Scales of Early Learning
and the Vineland Adaptive Behaviour Scales. We compare the performance of 2-3 year-olds with
Down syndrome with that of a MA-matched comparison group of 2 to 3-year-olds with
developmental disabilities, and an MA-matched group of typically developing 1 to
Materials and Methods
This study was part of a larger longitudinal study of the developing phenotypes of autism,
fragile X syndrome, and Down syndrome. Participants were recruited through the JFK Partners
University Affiliated Program and parent support groups in the Denver Metropolitan Area
(e.g., Mile High Down Syndrome Association, Fragile X Foundation). The entire study was
carried out under Institutional Review Board approval. Consent forms were reviewed with each
family and all questions were answered before consent was obtained and before any measures
were gathered. All examiners were completely blind to the questions being asked in this
study and limited knowledge regarding the Down syndrome behavioural phenotype (their
expertise was in children with autism).
The Mullen Scales were administered in a laboratory visit in a standardised fashion. All
examiners were masters or doctoral level clinicians with several years of clinical
experience working with young children with developmental disabilities. Mothers were
interviewed for the Vineland Scales, generally during a home visit.
Experimenters administered a battery of developmental tests including:
1. Mullen Scales of Early Learning (MSEL; Mullen, 1995). The MSEL is a standardised
developmental test for children ages 3 to 60 months consisting of five subscales: gross
motor, fine motor, visual reception, expressive language, and receptive language. The MSEL
allows for separate standard verbal and nonverbal summary scores to be constructed and
demonstrates strong concurrent validity with other well-known developmental tests of motor,
language, and cognitive development (Mullen, 1995). Internal consistency of the five subdomains ranges from .75 to .83, evidence that the subscales measure distinct abilities.
High correlations have been found between the MSEL and the Bayley Scales of Infant
Development, the Preschool Language Assessment, and the Peabody Fine Motor Scale.
The MSEL was administered to all subjects according to standard instructions by raters with
advanced degrees, trained in assessing young children with autism and other developmental
disorders. Reinforcers for all subjects in all groups were used at times to reward
cooperation and attention.
The Receptive Language Scale provides an assessment of a child's ability to decode verbal
input. The majority of questions require a nonverbal response (such as pointing), with the
exception of one higher-level item, which requires a child to answer questions in order to
ascertain their general knowledge skills. Tasks on this scale assess a child's understanding
of verbal instructions, auditory-spatial and auditory-quantitative concepts, memory for
commands and general concepts. Difficulty with items on this scale is hypothesised to be
related to impairments deriving linguistic meaning from spoken language (Mullen, 1995).
The Expressive Language Scale assesses a child's spontaneous language, specific vocal or
verbal responses to questions, and high-level concept formation (Mullen, 1995). The
expressive language tasks are all considered intrasensory, requiring the child to respond to
an auditory prompt or question. Expression is not completely independent of comprehension,
and auditory discrimination and vocal motor skills are necessary for responses on this
scale. Difficulties on this scale may be attributable to any of the following: difficulties
with syntax, dyspraxia, or auditory memory (Mullen, 1995).
The Visual Reception Scale focuses on visual perceptual ability with minimal response
requirements. Children are presented with visual information in various forms and patterns,
involving oculomotor and visual motor operations (e.g. localising on a target, visual
tracking, scanning multiple points on a surface). Tasks assess visual discrimination and
visual memory. Vocalisations are not required for responses but some instructions are given
verbally, accompanied by gesture and pantomimed instruction.
The Gross Motor Scale tasks assess skills including head control, sitting, pulling to stand,
rotating from sitting to hands/knees, and walking. The subtest is designed to measure the
organised progression of cephalocaudal and proximodistal motor development.
The Fine Motor Scale involves bilateral and unilateral manipulation. Bilateral items include
turning pages in a book, unscrewing/screwing a nut and bolt, stringing beads, folding, and
cutting. Unilateral items include stacking blocks, putting pennies in horizontal or vertical
slots, imitating block models, and drawing or writing. These tasks involve both motor
planning, or praxis skills, and motor control.
2. Vineland Scales of Adaptive Behaviour, Interview Edition. The Vineland (Sparrow, Balla &
Cicchetti, 1984) is a 291-item standardised parent interview for children ages birth to 18
years. The Vineland is designed to assess adaptive behaviour across four domains:
socialisation, communication, daily living, and motor skills. The Vineland provides
norm-referenced information based on the performance of representative national
standardisation samples of 4,800 typically and atypically developing children.
The Socialisation Domain assesses functioning in interpersonal relationships, play and
leisure time, and coping skills. For toddlers, interpersonal relationship items involve
dimensions like "laughs or smiles appropriately in response to positive statements", play
and leisure time items for toddlers involve dimensions like "participates in at least one
game or activity with others", and coping skills involve items like "says 'please' when
asking for something". For the daily living skills domain, toddler personal daily living
skills items include behaviours like "feeds self with spoon without spilling", the community
living skills items for toddlers involve dimensions like "demonstrates understanding of the
function of money", and the domestic daily living skills subdomain involves items like "puts
possessions away when asked". The communication domain involves expressive language items
like "says at least 50 words", and receptive language items like "points accurately to all
body parts when asked". The motor domain involves toddler gross motor items like "pedals
tricycle or other three-wheeled vehicle for at least six feet", and fine motor items like
"screws and unscrews lid of jar."
The Vineland was administered in order to understand how the children actually used their
skills in representative, generalised, real life settings, outside of the structure and
scaffolding provided in the laboratory situation.
3. Demographics Questionnaire. Parents were asked about information regarding parents' age,
SES (Hollingshead, 1975), education level, and ethnicity.
Participants. Participants were eighteen 2 to 3-year-old children with Down syndrome,
nineteen 2 to 3-year-old children with mixed etiologies of developmental delays, and 24
MA-matched typically developing infants and toddlers. There were no differences between
clinical groups on gender or child chronological age, and children in both disability groups
averaged a CA of around 33 months (See Table 1 for all demographic and developmental
information). Children in the typically developing group had an average CA of 19.5 months
(SD = 4.98). Children in all groups were also equated on MSEL mental age as well, averaging
an overall MA 21-23 months on the Mullen scales. Children in all groups all had normal
vision and hearing or vision corrected to within the normal range, had unimpaired hand use,
and were mobile.
F or X2
Child CA M in months
DS, DD >typ
DS, DD <typ
Premature birth % (n)
Overall Child MSEL MSEL MA in months (sd;
Father Age in years M
DS, DD >typ
Mother Age in years M
(4.43; 30-44 )
DS, DD >typ
SES (s.d.; min-max)
56.49 (7.00; 40-66)
50.37 (11.96; 15-66)
* p < .05, ** p < .01
Table 1 | Demographic and developmental information
All children with Down syndrome had a genetic diagnosis of trisomy 21. Within the
developmental disabilities comparison group, thirteen of the children had other genetic
abnormalities (fragile X syndrome without autism, Velo-cardiofacial syndrome, Cochayne
syndrome, partial deletion on chromosome 18, abnormalities on chromosome 15) and six had
developmental delays of unknown etiology. There were no differences in prevalence of
premature births (born before 36 weeks gestation) between the Down syndrome and other two
groups, X2 (2, n = 55) = 1.90, ns. In addition, there were no between-disability group
differences in the amount of early intervention services received for speech therapy, X2 (1,
n = 33) = 1.28, ns, occupational therapy, X2 (1, n = 33) = 1.13, ns; specialised preschool
attendance, X2 (1, n = 33) = .97, ns; public special ed preschool attendance, X2 (1, n = 33)
= 1.51, ns; structured home programs, X2 (1, n = 33) = 0.002, ns; mainstream preschool
attendance, X2 (1, n = 33) = .51, ns.
No between-group differences were observed on parent age and SES, though parents of
typically developing children were younger than parents in the disability groups (see
1 for parent demographic information). No relationship was found between child MSEL MA and
family SES in the Down syndrome group, r (16) = -.13, ns; the developmental disabilities
comparison group r (17) = .31, ns; and in the typical controls,
r (22) = -.01, ns. The lack
of relationship between SES and child functioning in the clinical groups most likely
reflects the strong biological origins of the children's disorders, though a modest
association was observed in the developmental disabilities comparison group, as might be
expected. SES is more often related to child developmental variables in children with milder
intellectual delays and those from a more impoverished background. Similarly, the lack of
relationships between SES and the typical children's functioning most likely reflects the
narrow range of SES and the middle class status of this group.
Mullen Scales. A 3 (Down syndrome versus comparison group versus typically developing
children) by 5 (5 MSEL domains) MANOVA was performed in order to assess specificity of MSEL
profiles across the three groups. Using Wilks' criterion, the profiles, seen in Figure 1,
deviated significantly from parallelism, F (4,55) = 8.28, p < .0001, observed power = .99
(see Table 2 for means and standard deviations). Post-hoc one-way ANOVA analyses suggest
that no significant differences were found between the Down syndrome and the other two
groups, and that the source of significant difference among the three groups was expressive
language differences between the typical and developmental disabilities groups,
F (2, 56) =
6.74, p < .005 (DD< typ).
Gross Motor M (s.d.)
Visual Reception M (s.d.)
Fine Motor M (s.d.)
Receptive Language M (s.d.)
Expressive Language M (s.d.)
* p < .05, ** p < .01
Table 2 | MSEL domain
In addition to exploring whether the Down syndrome outcomes were specific to that group, a
second analysis was conducted to explore within-Down syndrome variation in MSEL performance.
A one-way repeated measures ANOVA showed that children with Down syndrome did indeed show
distinct areas of strength and weakness within their profile, F (4, 14) = 3.44,
p < .05,
observed power = .71. On average, children with Down syndrome showed stronger performances
on the visual reception (age equivalent M = 21.22 months) and receptive language (age
equivalent M = 22.11 months) domains of the MSEL. Their performances on the MSEL gross motor
(age equivalent M = 18.22 months) and the expressive language subtests (age equivalent
19.33 months) were relatively weaker. Post-hoc analyses showed that children in this sample
showed a significant dissociation between receptive and expressive language,
t (17) = 3.17, p < .01; and between receptive language and gross motor skills,
t (17) = 2.48, p < .05.
Vineland Adaptive Behaviour Scales. A 3 (Down syndrome versus comparison group versus
typical) by 4 (Vineland domains) MANOVA was performed in order to assess specificity of
adaptive behaviour outcomes across the three groups. Using Wilks' criterion, the profiles
deviated significantly from parallelism, F (8, 196) = 8.00, p < .0001, observed power = .99.
Post-hoc one-way ANOVAs show that the source of significant difference among the three
groups lay in socialisation differences, F(2, 56) = 8.12, p < .001 (DS, typ >DD) and
communication differences, F (2, 56) = 4.89, p < .01 (typ>DD). Thus, the strength in social
relationships often associated with Down syndrome was demonstrated.
F (2, 58)
Communication M (s.d.)
Typ > DD
Daily Living Skills M (s.d.)
Socialisation M (s.d.)
Motor Skills M (s.d.)
* p < .05, ** p < .01
Table 3 | Vineland domain age-equivalent scores
Further analyses were conducted to assess the within-Down syndrome performance profile on
the Vineland. One-way Repeated Measures ANOVA showed that children with Down syndrome again
showed distinct areas of strength and weakness in functioning, this time in adaptive
behaviour, F (3, 19) = 3.89, p < .05, observed power = .79. Post-hoc analyses show that
children with Down syndrome had significantly stronger socialisation than communication
scores t (17) = 4.42, p < .0001, and stronger socialisation than motor skills scores,
= 2.87, p < .01.
One area of particular relative strength in socialisation involved Play and Leisure Time
items. Age equivalent scores for the Down syndrome group in this study on Play and Leisure
Time socialisation sub-domain averaged 23.8 months. In contrast, the interpersonal
relationship area of the Vineland socialisation domain showed average age equivalent scores
of 18.7 months. A paired-sample t-test shows significant within subject differences on these
two aspects of socialisation, t (17) = 3.38, p < .005.
Similarly, within the Vineland communication domain, children in the Down syndrome group
showed dissociations between receptive and expressive language, t (17) = 5.15,
p < .0001. As
observed with the MSEL, these children had significantly higher receptive language
communication sub-domain scores (M = 26.1 months) than expressive language communication
sub-domain scores (M = 16.1 months). It should be noted that some discrepancy between parent
report and child battery scores were observed on communication domains. Though these
discrepancies were found, parent report and child battery measures were highly correlated
for the Down syndrome group, for receptive language, r (16) = .83,
p < .0001, and expressive
language, r (16) = .82, p < .0001; and collapsed across all groups for receptive language,
(59) = .70, p < .0001, and expressive language, r (59) = .85,
p < .0001.
Previous studies have reported a specific behavioural phenotype, or distinct areas of
relative strength and weakness in cognition, language, social functioning, and motor skills,
associated with the diagnosis of Down syndrome. However, these findings have focused
primarily on older children and young adults. This study was designed to examine the origins
of that phenotype by examining the developmental and behavioural profiles of toddlers with
Down syndrome. Is the specific phenotype present at the earliest points in development that
it can be measured, as intentional communication is emerging and thus represents a 'starting
state'? Or does it develop more slowly across the preschool years, as various developmental
skills become more practised and as they acquire their own experiential history?
The performance of young children with Down syndrome in this study was compared to the
performance of a comparison group of children with other developmental disabilities and a
group of typically developing children, all matched for developmental levels. Children's
performance was assessed on both laboratory administered measures and on parent reports of
naturally occurring behaviours in real life situations.
In terms of specificity, the children with Down syndrome in this study showed significantly
higher Vineland Socialisation scores than the developmental disabilities comparison group.
No other areas of functioning distinguished the Down syndrome group from the other two
groups. These findings suggest that while some specificity was observed in socialisation,
for the most part the specificity of the Down syndrome profile in toddlerhood was not
established in this study.
However, when the profile within Down syndrome was examined, children with Down syndrome in
this study did show relative strengths on the laboratory based developmental measure in the
areas of visual processing and receptive language, and relative weaknesses in gross motor
skills and expressive language. In terms of parent reported skills in adaptive behaviour in
real-life situations, the children with Down syndrome in this study showed relative
strengths in socialisation and relative weakness in communication and motor skills. Thus,
there is evidence that the behavioural phenotype associated with Down syndrome is emerging
by the age of three, with between-group differences in sociability, and within-group
patterns of relative strengths and weaknesses that foreshadow the phenotype described in
studies of older persons.
This paper is part of a larger movement toward viewing behavioural phenotypes from a
developmental perspective. Recently, researchers have begun to call for a reframing of
phenotype research to include the neglected aspect of development. As an example,
Karmiloff-Smith (1997) has argued for the importance of studying the development of the
language in Williams syndrome – that many young children with Williams syndrome do not show
the pronounced relative strength in language, but these phenotypic outcomes emerge and
become pronounced during development. Studies to date that have taken a developmental
approach to behavioural phenotypes have similarly found that areas of strength develop at a
faster rate than areas of weakness over time in fragile X syndrome and Down syndrome
(Hodapp, Leckman, Dykens, Sparrow, Zelinsky & Ort, 1992;
It is notable that two of the dissociations observed within the individuals with Down
syndrome were significant, but also relatively small at these early developmental ages. Even
in the significant difference between expressive and receptive language, differences
averaged only 2.5 months. In other studies with older children with Down syndrome,
dissociations between domains of functioning can be much larger. This does not minimise the
rapid changes that take place over several months in early development. But the relatively
small dissociation is also notable for intervention purposes – because areas of strength and
weakness are less pronounced early on, it may be possible to reduce these dissociations and
set areas of potential weakness on more optimal pathways. That small dissociations early in
development can result in increasingly larger differences over time is consistent with
dynamic systems theory in that small starting state differences can evolve considerably as
development becomes increasingly complex and differentiated.
Though several features of the Down syndrome behavioural phenotype were observed in this 2
to 3-year-old sample, other dissociations that are observed in later development did not
seem to be present at this age. We did not observe differences in performance on visual
processing versus receptive language tasks. The expected dissociation between visual and
verbal processing in Down syndrome, according to our results, was not yet present. This,
too, may have important implications for intervention. Alternatively, the lack of observed
dissociation may also result from administrative aspects of the MSEL receptive language
scale, which include modeling, gesturing, and parent report.
Several limitations to this study must be noted. First, our measure of adaptive behaviour,
the Vineland Adaptive Behaviour Scales, is a parent report measure, based on generally
observed behaviour rather than explicitly elicited and scaffolded behaviour, and this may
account for discrepancies in age-equivalent scores across the two measures. Second, these
measures reflect general functioning in several broad areas, and future studies should
explore patterns of performance within these broad categories. Third, these findings are
based on relatively small sample sizes and are only suggestive, not conclusive. Findings
need to be replicated with a larger sample size.
This study contributes to the larger movement toward examining behavioural phenotypes in
children with genetic syndromes. In describing the particular behavioural outcomes
associated with genetic syndromes, we gain information needed to develop targeted
educational and intervention programs for specific learning profiles. By understanding the
early developmental trajectory of a particular set of outcomes, we may be able to develop
interventions that are time-sensitive, and that prevent or offset potential future delays.
These findings have stimulated several questions for future studies. Two of the most
pressing involve the stability of individual profiles of strengths and weaknesses over time,
and the determination of environmental and biological events that affect the development and
stability of the profile of abilities.
Deborah J. Fidler, Ph.D. • 102 Gifford Building, 502 West Lake Street, Colorado State
University, Fort Collins, CO, 80523 • E-mail: Deborah.Fidler@colostate.edu.
Dr. Rogers and Dr. Hepburn are partially supported by NICHD U19 HD35468, and by NIDCD R21
05574. The intellectual support of the Developmental Psychobiology Research Group is
gratefully acknowledged. This program of research is part of the Collaborative Programs of
Excellence in Autism. The authors also thank Amy Philofsky, Galit Mankin, and Athena Hayes
for their contributions to this project.
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