Sequence of cognitive decline in dementia in adults with Down's syndrome.
Watch Block Design and Coding first—these WISC-R subtests dip earliest when dementia appears in adults with Down syndrome.
01Research in Context
What this study did
The team tracked WISC-R scores in adults with Down syndrome over time.
They wanted to see which subtests slip first when dementia starts.
The study used a quasi-experimental design to map the order of decline.
What they found
Block Design and Coding are the first two subtests to fall.
As dementia moves into later stages, more WISC-R tasks follow.
The drop follows a clear, predictable pattern you can watch for.
How this fits with other research
D'Agostino et al. (2025) built on this idea by creating the ND-PROM. Their tool separates ASD signs from general delay in kids with Down syndrome.
Eussen et al. (2016) also stretched assessment work into childhood. They showed the Dutch CDI captures both spoken and signed words in toddlers with Down syndrome.
Landry et al. (2016) used a different test, the WCST, in autism. Their meta-analysis found medium-sized deficits, proving cognitive-test profiling works across diagnoses.
Why it matters
You now know which WISC-R subtests to monitor first in adults with Down syndrome. Flagging early drops in Block Design or Coding gives you a heads-up before fuller dementia sets in. Share the pattern with families and medical teams so everyone can plan sooner.
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02At a glance
03Original abstract
Adults with Down's syndrome (DS) are known to be at risk of dementia of the Alzheimer type (DAT), but because of their lifelong intellectual deficits, it is difficult to determine the earliest signs and characteristics of age-associated decline and dementia. In a longitudinal study in which all participants were healthy at the time of their entry into the study, the present authors compared the amount of decline on the subtests of the WISC-R to determine the sequence of cognitive decline associated with varying stages of dementia. Twenty-two individuals with varying degrees of cognitive decline were compared to 44 adults with DS who have remained healthy. All participants functioned in the mild or moderate range of intellectual disability at initial testing. On each subtest of the WISC-R, the amount of change experienced by the healthy participants over the study period was compared to the amount of change found for each of the groups with decline. Out of the individuals who showed declines, 10 adults with DS were classified as having 'questionable' decline based on the presence of memory impairment, and five and seven adults with DS were classified as in the 'early stage' and 'middle stage' of DAT, respectively, based on the presence of memory impairment, score on the Dementia Scale for Down Syndrome and a physician's diagnosis. It was found that participants who were identified as 'questionable', in addition to the memory loss that determined their classification, also showed significant declines on the Block Design and Coding subtests. The five adults in the early stage of dementia showed declines on these subtests, and in addition, on the Object Assembly, Picture Completion, Arithmetic and Comprehension subtests. The seven adults in the middle stage of dementia showed declines on these subtests, plus declines on Information, Vocabulary and Digit Span subtests. The Picture Arrangement and Similarities subtests were not useful in distinguishing between the groups because of baseline floor effects for a substantial proportion of participants. The present longitudinal study showed a sequence of cognitive decline associated with DAT, beginning with a possible 'pre-clinical' stage, and progressing through the early and middle stages. This approach begins to define the sequence of declining cognitive capacities that contributes to the observed functional deterioration caused by Alzheimer's disease and that is likely to reflect the involvement of cortical areas as the disease progresses.
Journal of intellectual disability research : JIDR, 2000 · doi:10.1046/j.1365-2788.2000.00305.x