O’Caoimh et al., J Alzheimers Dis Parkinsonism 2013, S7
http://dx.doi.org/10.4172/2161-0460.S7-001
Alzheimer’s Disease &
Parkinsonism
Review Article
Open Access
Screening for Alzheimer’s Disease in Downs Syndrome
Rónán O’Caoimh, Yvonne Clune and D. William Molloy*
Centre for Gerontology and Rehabilitation, St Finbarrs’ Hospital, Cork City, Ireland
Abstract
Downs syndrome (DS), is associated with an increased incidence of Alzheimer’s disease (AD). Although pathological changes
are ubiquitous by 60 years of age, prevalence rates are lower. The diagnosis of AD in persons with DS is challenging, complicated by
atypical presentations, baseline intellectual disability and normal age associated cognitive decline. Effective screening is limited by
a paucity of diagnostic criteria, cognitive screening instruments and screening programmes. Both observer-rated questionnaires and
direct neuropsychological testing are suggested to screen for cognitive impairment, each with different strengths and weaknesses.
This paper reviews commonly used screening instruments and explores the unique challenges of screening for AD in persons with
DS. It concludes that single, one-dimensional screening tools and opportunistic evaluations are insufficient for detecting dementia
in this population. These should be replaced by batteries of tests, incorporating informant questionnaires, direct neuropsychological
testing, assessment of activities of daily living and behaviours, measured at baseline and reassessed at intervals. Developing these
strategies into organized screening programmes should improve diagnostic efficiency and management.
Keywords: Downs syndrome; Alzheimer’s disease; Dementia;
Cognitive screening instruments; Review
Introduction
Downs syndrome (DS) is the most common genetic disorder seen
in clinical practice and is associated with an increased incidence of
dementia, notably Alzheimer’s disease (AD). Onset is earlier than in
the general population [1] and recent advances in healthcare, which
have seen average life expectancy for people with DS rise close to 60
years, [2] have increased its prevalence. In the context of the four lifestages described in DS, the last (> 40 years of age), senescence [3], is the
typical stage of onset of AD.
The diagnosis of dementia in individuals with DS is difficult
and is complicated by baseline intellectual disability (ID) [4]. No
guidelines, within the DSM 4 or ICD 10 classifications, currently exist
for diagnosing dementia associated with DS or any other learning
disability. Thus, depending on the criteria employed and the population
studied, prevalence of AD varies from 7% [5] to as high as 55% after 60
[6] and 75% by 65 years [7]. The unadjusted average prevalence rate of
AD in DS is approximately 15% [8]. Prevalence rates for AD associated
with DS also vary depending upon age [9] and baseline cognition
[10]. Histopathogical studies have confirmed that hallmark changes
consistent with AD are present in DS as young as the second decade
of life and are found in 100% of cases by 60 years of age [11]. Despite
this, just over half have clinical evidence of dementia and many living
beyond 70, will never develop clinical AD [12]. Poor screening may
account for underestimating the true prevalence [6].
Efficient and effective screening for AD in DS is required to
diagnose, manage and exclude reversible causes. Although no specific
guidelines exist, a clinical diagnosis is likely in the presence of new
and progressive memory loss associated with deterioration across
cognitive domains and activities of daily living (ADLs). Management of
dementia including AD is similar to the general population, requiring
prompt initiation to maximize benefit and is predominantly supportive.
Although there is little strong evidence that pharmaceutical therapies,
including cholinesterase inhibitors [13] and memantine [14], benefit
those with DS patients with AD, treatment is often delayed, arguably
reducing the therapeutic window [15]. Their use, as in the general
population, requires knowledge of the disease stage. Older adults with
DS often have significant co-morbidities [3] and it is important to also
manage these. Although the prevalence of atherosclerotic complications,
including cerebrovascular disease and vascular dementia, is low [7,16],
J Alzheimers Dis
older adults with DS have a relatively high prevalence of heart disease
[17], obesity [18] and diabetes [19] for their age. Conditions mimicking
dementia, such as thyroid disease, are also prevalent in DS and are
frequently under-diagnosed. The lifetime prevalence of thyroid disease
approaches 30% [20] and hypothyroidism in particular, is underdiagnosed. Depression, which can also mimic dementia, is common in
DS [21] and should be screened for and treated.
Presentation of Dementia in DS
The predominant cognitive deficits in DS are in verbal shortterm memory, explicit long-term memory and morphosyntax.
Visuospatial, short-term memory, associative learning, and implicit
long-term memory functions are usually preserved [7]. As with nondemented older adults, normal age associated cognitive changes are
common in ageing adults with DS. Over the age of 40, the rate of
decline, on neuropsychological testing, approaches 11% per year [22].
A selective pattern of cognitive changes is usually seen, characterized
by impairment in long-term memory and visuospatial construction
with relative preservation of immediate memory (recall) and language
[23]. When dementia develops in adults with DS, it is characterized
by global neuropsychological deficits, albeit with retention of some
basic language skills [23], and often presents atypically [17]. Unlike
the majority of cases of AD, people with DS developing AD, often
present with frontal symptoms rather than with short-term memory
loss [24]. This means that behavioural symptoms predominate [17],
making it more challenging to separate AD from new onset behavioural
disorders, or other psychiatric conditions such as depression, which
are common in older adults with DS [25]. Deterioration in those with
AD is associated with both age [26] and baseline cognitive ability [10].
Other atypical presentations include seizures and myoclonus, which are
often a surrogate marker for the onset of dementia [27].
*Corresponding author: D William Molloy, Centre for Gerontology and
Rehabilitation, St. Finbarr’s Hospital, Douglas Road, Cork, Ireland, Tel: 00353 21
4627347; E-mail: w.molloy@ucc.ie
Received January 18, 2013; Accepted February 06, 2013; Published February
15, 2013
Citation: O’Caoimh, Clune Y, Molloy D.W (2013) Screening for Alzheimer’s Disease
in Downs Syndrome. J Alzheimers Dis Parkinsonism S7: 001. doi:10.4172/21610460.S7-001
Copyright: © 2013 O’Caoimh, et al. This is an open-access article distributed under
the terms of the Creative Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium, provided the original author and
source are credited.
Down Syndrome
ISSN:2161-0460 JADP an open access journal
Citation: O’Caoimh, Clune Y, Molloy D.W (2013) Screening for Alzheimer’s Disease in Downs Syndrome. J Alzheimers Dis Parkinsonism S7: 001.
doi:10.4172/2161-0460.S7-001
Page 2 of 6
General Principles of Cognitive Screening in Persons
with DS
compliance, dexterity, attention and language skills have not been
validated in those with DS.
There is a need for coordinated healthcare screening, tailored to
individuals with learning impairment [28] including DS. Dementia
screening projects for people with DS highlight the lack of screening
for dementia and other conditions [29]. Studies suggest a need to
develop longitudinal rather than isolated, opportunistic screening
approaches so baseline skills and abilities can be mapped and objective
changes demonstrated to identify new cognitive impairments and
evolving dementia. Some have suggested establishing this baseline by
the age of 35 with annual reassessments [30], others that assessment
should start at 25 with reevaluation at least every five years [4]. When
change is established, a diagnosis is sought and appropriate personcentred care is provided to both client and caregiver alike [30]. As the
presentation of dementia in DS is often atypical [17], when screening
for dementia, it is important to consider changes in not only cognition
but also personality, behaviour and ADLs. Sensory impairments such
as hearing and visual problems are common [31] and may affect the
ability to participate in cognitive testing. Screening is important as it
allows prompt and appropriate initiation of care and treatment. Prompt
assessment allows for the identification and exclusion of reversible
causes.
Clinicians require reliable and valid screening instruments that
are responsive to change, measure a wide range of cognitive domains,
identify changes early (high ceiling) and throughout the later stages of
dementia (low floor). Although several screening tests for use in DS
have been described, the agreement between different screening tests is
reasonable and is generally in the order of between 70-75% [37]. Floor
effects (high floor) are seen to a variable degree with most instruments
developed or adapted for assessing cognition in DS. Screening or
diagnostic tools suitable for screening for dementia in DS, can be either
directly administered neuropsychological tests, or informant based
observer-rated scales. When different instruments were compared,
the observer-rated scales were superior to direct testing in assisting in
the diagnosis of dementia in people with intellectual disability [37].
Individual screening instruments may not produce the most accurate
results when screening for cognitive impairment in DS and have
compared poorly to clinical judgment, which alone was found to be
superior to a range of different tests [38]. Combined assessment using
observer-rated questionnaires and direct neuropsychological testing
may provide the highest sensitivity and specificity [37].
Screening Tools in DS
As many neuropsychological tests are not suitable or have not been
validated for use in persons with developmental ages less than five or
six [39], a collateral history is crucial to a diagnosis of dementia in
persons with any ID, including DS. Given this, observer-rated scales,
also called informant guided questionnaires or interviews, are often
preferred over direct neuropsychological testing. Observer-rated scales
must however, be interpreted with caution as ageing caregivers may be
developing cognitive difficulties themselves or may know the subject
too well or insufficiently to be objective [8]. Multiple informants should
be consulted when subjects reside in institutional care [40]. While they
include cognitive domains, they do not directly test cognition [27].
Several observer-rated scales have been developed, each with their own
strengths and weaknesses (Tables 1 and 2).
Screening tools, specifically designed for detecting onset of
dementia in persons with DS differ from screening tools for dementia
in individuals without ID. In particular, they do not rely on cut-off
scores but instead are based on combined functional and cognitive
testing, ideally measuring change by comparing baseline with current
status. Traditional screening instruments for detecting dementia, (like
the Mini-Mental Status Exam (MMSE) [32] and its standardized form,
the SMMSE [33]), or mild cognitive impairment (like the Montreal
Cognitive Assessment [34] or Quick Mild Cognitive Impairment screen
[35,36] were designed for people with average baseline intelligence and
are of limited use in older adults with DS. These tests require developed
language skills and attention, which can be impaired in individuals with
ID [7]. The commonly used MMSE performs poorly when compared
with observer-rated scales and could only be completed in 55% of
test subjects with DS [37]. Other screening instruments that require
Classification
Observer rated
scales
J Alzheimers Dis
Instrument
Advantages
Observer-rated Scales
Dementia Scale for Down Syndrome
The Dementia Scale for Down Syndrome [41] (DSDS) is a useful
Disadvantages
Sensitivity
For AD In DS
Specificity For
AD In DS
Reference
DSDS
-Comprehensive
-Scores new behaviours
-Measures from early to late stage
-Includes differential
diagnosis scale
- No significant floor effect
-No measure of general disability
-Cut-off varies
-Little emphasis on change [43]
-Restrictions on use (specialized rater)
-Some redundant items[37]
-Lengthy (up 30 mins) administration
time
89%
85%
Gedye [41]
DMR
-Includes measure of general
disability
-Emphasis on memory
-Orientation assessed
-No restrictions on use
-Brief administration time (15-20 mins)
-Requires repeat measures over time
[43]
-Behavioural disturbance questions
have poor reliability
-low specificity in low-moderate ID
-Floor effects
92%
92%
Evenhuis [42]
CAMDEX-DS
-Includes measure of general
disability
-Strong emphasis on change
-Can be used to predict cognitive
decline
-Excellent IRR
-Diagnostic rather than a screening tool
-Initially designed for the general adult
population
-Floor effects
-Lengthy administration time
88%
94%
Roth et al. [43]
Ball et al. [44]
DSQIID
-Validated in a large sample
-Single fixed cut-off may limit in
-Excellent IRR
advanced dementia & those with
-Brief administration time (10-15 mins) different baseline disability
92%
97%
Deb et al. [31]
Down Syndrome
ISSN:2161-0460 JADP an open access journal
Citation: O’Caoimh, Clune Y, Molloy D.W (2013) Screening for Alzheimer’s Disease in Downs Syndrome. J Alzheimers Dis Parkinsonism S7: 001.
doi:10.4172/2161-0460.S7-001
Page 3 of 6
DSME
-Limited number of domains
-Over emphasis on verbal skills
-Poor sensitivity compared to other
tests [27]
-Floor effects
-Easy to administer
NA
NA
See for
CAMDEX-DS
See for
CAMDEX-DS
TSI
-Wide range of scores
-Requires little speech
-No measure of general disability
-No significant floor or ceiling
-Designed for the general adult
effects
population
-Brief administration time (10 mins)
NA
NA
ABDQ
-Effects of variables (age, race)
-Excellent accuracy (92%)
undetermined
-Brief administration time (10 mins)
-No assessment of cognition
-Designed specifically for AD
-No measure of general disability
-Excellent IRR
89%
94%
DLSQ
-No significant floor effect
-High positive predictive value
-Correlates strongly with direct
cognitive tests
NA
NA
Neuropsychological component
of the
CAMDEX
Neuropsychological
CAMCOG-DS -Quantitative score that can be
tests
tracked longitudinally
-Differentiates older from younger
persons with DS
Adaptive behaviour
tests
-Limited assessment of executive
function
-Limited generalizability to those with
late dementia
-Initially designed for the genera
l adult population
-No assessment of cognition
-No measure of general disability
Haxby [23]
Hon et al. [45]
Ball et al. [24]
Albert and
Cohen [47]
Prasher et al.
[51]
National Institute
of Ageing [53]
Table 1: Comparison of the advantages and disadvantages of different assessment instruments for dementia in persons with Downs syndrome.
Classification
Observer rated scales
Neuropsychological tests
Adaptive behaviour tests
General
Disability assessment/
global assessment
Instrument
Cognition
assessed
Behaviour
assessed
ADLs
assessed
DSDS
+
+
+
-
Gedye [41]
DMR
+
+
+
+
Evenhuis [42]
CAMDEX-DS
+
+
+
+
Roth et al. [43]
Ball et al. [44]
DSQIID
+
+
+
-
Deb et al. [31]
DSME
+
-
-
-
Haxby [23]
-
-
Hon et al. [45]
Ball et al. [24]
Albert and Cohen [47]
CAMCOG-DS
+
-
Reference
TSI
+
-
-
-
ABDQ
-
+
+
-
Prasher et al. [51]
DLSQ
-
+
+
-
National Institute of Ageing [53]
+ Domain included
- Domain not included
Table 2: Domains included in different screening and assessments instruments for dementia in persons with Downs syndrome.
test for measuring progression of AD in DS. It comprises of 60
questions divided equally into three categories indicating the stage of
dementia from early to late. Behaviours, present for at least six months,
are rated as ‘present’, ‘absent’, ‘not applicable’ or’ typical’ with only those
marked ‘present’ contributing to the score. The DSDS has a specificity
of 89% and a sensitivity of 85% in identifying dementia in persons with
intellectual disability, including DS and closely correlates with the DMR
[37]. The DSDS, while comprehensive contains no measure of general
disability and the screening cut-off varies resulting in variations in
sensitivities reported. Restrictions on the use of the DSDS apply and
it is not recommended for use by those inexperienced in the use of
standardized intelligence tests [41].
Dementia Questionnaire for Mentally Retarded Persons
The Dementia Questionnaire for Mentally Retarded Persons
(DMR) [42] is an English translation of a Dutch questionnaire, the
Dementie Vragenlijist voor Zwakzinnigen (DVZ). It is based upon the
observations of caregivers over the previous two months. The DMR
has a specificity and sensitivity of 92% for the diagnosis of dementia in
J Alzheimers Dis
persons with ID, including DS, and compares favourably with the DSDS
and MMSE [37]. The questionnaire has 50 items (8 subscales) divided
into two subcategories: cognitive scores (short term memory, long-term
memory, spatial and temporal orientation) and social scores assessing
speech (including conversation), practical skills, mood, activities,
interests and behaviours. The questionnaire provides three response
categories, ranging from zero (no deficit) to two (severe deficit), with
higher scores corresponding to greater severity. The DMR, unlike the
DSDS, doesn’t require specialised training, contains a useful measure of
general disability and is also quick to use (15-20 minutes). It is poorly
sensitive in advanced dementia due to floor effects, necessitating the
use of cut-off scores adjusted to the level of ID. An abbreviated form is
also available.
The CAMDEX-DS
A modified version of the informant interview of the Cambridge
Examination for Mental Disorders of the Elderly [43], the CAMDEXDS [44] can be used to document increasing prevalence with age [9].
The CAMDEX-DS, designed for use in the community, by trained
Down Syndrome
ISSN:2161-0460 JADP an open access journal
Citation: O’Caoimh, Clune Y, Molloy D.W (2013) Screening for Alzheimer’s Disease in Downs Syndrome. J Alzheimers Dis Parkinsonism S7: 001.
doi:10.4172/2161-0460.S7-001
Page 4 of 6
healthcare professionals, consists of both an informant interview and
participant neuropsychological assessment. It assesses memory, general
intellectual function, judgment, general performance, higher cortical
function and personality. The CAMDEX-DS has good interrater
reliability and predictive validity [44], when conducted with an
informant who knows the subject for at least six months. The authors
caution that it is a diagnostic aid rather than a screening tool. A floor
effect is also demonstrated with the CAMDEX-DS.
Dementia Screening Questionnaire for Individuals with
Intellectual Disabilities
The Dementia Screening Questionnaire for Individuals with
Intellectual Disabilities (DSQIID) [31] was derived from interviews with
caregivers of 24 adults, aged between 48 and 72, with DS and dementia.
It has 53 items, divided into three parts and has excellent internal
consistency, test-retest reliability and interrater-reliability. The first part
assesses baseline ‘best’ ability; the second part scores behaviours and
symptoms suggestive of dementia (43 questions, scored on a four point
scale with “always has been the case” and “does not apply” scoring zero
points and “always but worse” and “new symptoms” scoring one). The
third part provides ten comparative questions answered yes (one point)
or no (zero points). Scores from part two and three are summed to
provide a total score. A cut-off score of 20 provides optimal sensitivity
and specificity, 92% and 97% respectively. The DSQIID was validated
in a large sample of DS subjects with dementia, larger than either the
DSDS or DMR. The DSQIID is quick (10-15 minutes) and is easy to
score in any setting. The single, fixed cut-off, may limit its usefulness
in more advanced stages of dementia and in individuals with varying
degrees of baseline ID.
of 24 points. Eight questions require the subject to respond verbally.
Brief and easy to use without significant ‘floor’ or ‘ceiling’ effects [27],
it provides a wider range of scores than tests such as the DSMSE [48].
It also has excellent reported internal consistency, interrater reliability
and test-retest reliability [27].
The DAMES Score
The DAMES (Down’s syndrome attention, memory, and executive
function scales) score [22] is a neuropsychological test, validated
specifically in older adults with DS. Consisting of 11 domains, it
has three summaries (attention, executive function, and memory),
providing a total score of between 0 and 222. Higher scores indicate
better cognition.
Excluding Depression
As with dementia screening for the general population, it is
important to exclude co-morbid depression. Separating dementia from
other psychiatric conditions, particularly depression is challenging.
Depression is common in DS [25], frequently undertreated [21] and
associated with dementia [49]. The highest prevalence is seen in
those with mild to moderate ID [25]. Those with DS are vulnerable
to depression and several risk factors have been proposed including
small hippocampal volumes, changes in neurotransmitter systems,
deficits in language and working memory, attachment behaviours and
somatic disorders [21]. Depression in adults with DS usually presents as
a decline in social discourse [50]. Few instruments have been validated,
to differentiate between dementia and depression, in adults with DS.
Measures of Adaptive Behaviour
The Down Syndrome Mental Status Examination (DSMSE) [23],
comprises several cognitive domains including: orientation (days of the
week, seasons), personal information, short-term memory, language
(confrontation naming of clothing and body parts), visuospatial
construction and praxis. It has a strong emphasis on verbal skills. The
test was validated in a small initial sample, demonstrates a floor effect
and is less sensitive than other neuropsychological tests [27].
Decline in adaptive functioning beyond baseline levels is a
diagnostic feature of dementia. Tests of adaptive behavior measure
an individuals’ ability to function socially and perform ADLs. The
Adaptive Behaviour Dementia Questionnaire (ABDQ) [51] is a 15-item
questionnaire, derived from the Adaptive Behaviour Scale [52], and
used to detect change in adaptive behavior in DS. The ABDQ is reliable
and valid, demonstrating excellent accuracy (92%), in identifying
dementia in older adults with DS. The Daily Living Skills Questionnaire
(DLSQ) [53] is also of use in measuring ADLs [27,54]. Informants
provide information concerning a variety of ADLs including dressing,
grooming, eating, manual dexterity and geographical orientation.
The CAMCOG-DS
Conclusion
The Cambridge Cognition Examination or CAMCOG, the selfcontained neuropsychological component of the CAMDEX, has been
validated in subjects with DS [24,45]. The CAMCOG-DS contains seven
different subscales including orientation, language, memory, attention,
praxis, abstraction and perception, which were either taken directly
from the CAMCOG or modified from the Severe Impairment Battery
[46]. The total score is 107 points. Although some tests of executive
function were deemed too difficult and were removed, verbal fluency
and ‘similarities” remain as surrogate tests of executive function. The
CAMCOG-DS has few floor effects and correlates with the age and
MMSE scores [45].
Cognitive screening in persons with DS or other intellectual
disabilities is challenging and presents several important obstacles.
Baseline cognition limits both initial and interval assessments, making
the diagnosis difficult. DS is also associated with a normal-age related
cognitive decline and differentiating this from dementia is equally
challenging. As AD often presents atypically in DS, with frontal type
behavioural disturbance and loss of function, onset can be overlooked
or misattributed. The rules that normally govern cognitive screening,
such as the use of age and education adjusted cut-off scores [55], are
difficult to define and apply in DS. Floor effects, language skills, and
assessment variability due to behavior and cooperation also limit tests
[56]. The evidence base for treatment of AD in DS is as yet unclear, and
can be attributed to insufficient or delayed treatment [15], highlighting
the need for prompt screening and detection to ensure better outcomes.
Finally, healthcare professionals may not feel that screening for AD is
a priority or presume its inevitability in all older adults with DS. To
overcome this, campaigns such as the United Kingdoms “It’s your
move: Down’s syndrome and dementia” programme, were developed
Neuropsychological Tests
The DSMSE
The Test for Severe Impairment (TSI)
The Test for Severe Impairment or TSI [47], originally developed
for use in the general adult population, has been validated in persons
with ID [27]. The TSI consists of six subsections, including motor
performance, language, immediate and delayed recall, conceptualization
and general knowledge, each with four questions providing a total score
J Alzheimers Dis
Down Syndrome
ISSN:2161-0460 JADP an open access journal
Citation: O’Caoimh, Clune Y, Molloy D.W (2013) Screening for Alzheimer’s Disease in Downs Syndrome. J Alzheimers Dis Parkinsonism S7: 001.
doi:10.4172/2161-0460.S7-001
Page 5 of 6
to increase awareness of screening issues, particularly in primary care.
This is important, as cognitive screening should also be considered an
appropriate time to initiate general health screening in all older adults
with DS. Guidelines such as the Edinburgh Principles [57] provide a
useful ethical framework to guide care of persons with DS and AD.
Further research is needed to determine if long-term screening
programmes for AD or other forms of dementia in adults with DS will be
clinically or cost-effective. At present, no rapid screening tool has been
validated in this population and it is uncertain at which age screening
should begin. It is likely that no single, one-dimensional screening tool
will suffice. As with screening for dementia in the general population,
identifying early dementia is most challenging [37]. Given that clinical
judgment alone is currently superior to screening tests [38], it would
seem that there is a need to combine detailed clinical assessment
with informant history and standardized neuropsychological testing
to improve diagnostic accuracy. Although a working battery of tests,
like that proposed by the International Disability and the American
Association on Mental Retardation [30] can be used, they are limited by
time constraints. Instruments measuring functional level, scored in the
context of suggestive clinical features like age and new onset epilepsy
[27] may prove the most useful.
The course of AD in DS is not detached from the wider study of
dementia. Understanding of its onset, progression and management in
DS will also improve and further the management of AD in the general
population [58]. Only if the diagnosis is made early, will it be possible
to intervene and improve management, with both pharmacological and
non-pharmacological therapies, to benefit both older adults with DS
and caregivers alike.
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doi:10.4172/2161-0460.S7-001
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Citation: O’Caoimh, Clune Y, Molloy D.W (2013) Screening for Alzheimer’s
Disease in Downs Syndrome. J Alzheimers Dis Parkinsonism S7: 001.
doi:10.4172/2161-0460.S7-001
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