Down Syndrome Abstract
of the Month: July 2001

Alzheimer dementia in Down's syndrome: the relevance of cognitive ability

Temple V, Jozsvai E, Konstantareas MM, Hewitt TA
J Intellect Disabil Res 2001 Feb;45(Pt 1):47-55

Surrey Place Centre, Toronto, and Dept. of Psychology, Univ. of Guelph, Ontario, Canada

Abstract:

More years of education have been found to be associated with a lower rate of Alzheimer disease (AD) in individuals without intellectual disability. It has been proposed that education reflects greater 'synaptic reserve' and that greater synaptic reserve may defer the development of AD. The present study compared individuals with Down's syndrome (DS) who were found to have symptoms of dementia with those who remained symptom-free to determine if the two groups differed in their level of education, employment, recreational activities, years in an institution or overall level of cognitive functioning. Thirty-five adults with DS aged between 29 and 67 years were assessed. The participants were recruited from a community health facility and included individuals with a wide range of ability levels. Neuropsychological testing, caregiver report and the Dementia Scale for Down Syndrome were used to identify decline in participants over periods of 6 months to 3 years. After the effect of age was statistically removed, multiple regression analyses revealed that level of cognitive functioning was significantly associated with decline such that a higher level of cognitive functioning predicted less decline. None of the environmental variables (i.e. educational level, years in an institution and employment) were directly associated with decline; however, a post hoc regression using level of cognitive functioning as the outcome variable revealed that level of cognitive functioning itself was associated with these environmental variables. A higher level of cognitive functioning was associated with fewer cases of dementia in individuals with DS, and level of cognitive functioning appears to be associated with environmental factors such as level of education, years in an institution and employment. The present findings suggest that environmental interventions aimed at improving level of cognitive functioning may also be useful in deferring the onset of dementia.

My comments:

In simple terms, this study shows that adults with DS who are higher functioning at the onset of dementia are less affected by the dementia than adults with DS with lower cognitive skills. While the other possible environmental factors, such as education and work, had no direct effect on the onset or level of dementia, they may have had an indirect effect by increasing the level of functioning of the adult in the first place.

Of the 35 adults examined, the youngest adult to be definitely diagnosed with early dementia was 44 years old. Seven adults younger than 44 years were classified as having "possible" dementia, showing how hard it can be to make this diagnosis in adults with DS. All adults were examined to ensure no medical cause was responsible for a decline in skills.