Prevalence of dementia in adult patients with trisomy 21.

Neuropathological lesions characteristic of Alzheimer's disease (AD) are found in all the brains of patients with trisomy 21 who die after age 40 years. However, clinical signs of AD are much less frequent in these patients. Previous studies indicate prevalence figures ranging from 15% to 51% of adult patients. We report here on the prevalence rate of dementia in a population of adult patients with trisomy 21 with mild retardation living at home. For all these patients accurate and reliable anamnestic data could be obtained from parents and caregivers. All underwent neurological examination, cognitive testing, and, if necessary, further bioimaging and neurophysiological studies. Dementia was diagnosed according to clinical NINCDS/ADRDA criteria slightly modified. Dementia was found in 9 of 50 (18%) patients age 20-52 years, but its prevalence increased from 0 in the age group 20-29, to 33% in the age group 30-39, and to 55% in the age group 40-52. All the demented patients had signs of brain atrophy on CT scans and slow EEGs. Dementia is an important problem for patients with trisomy 21 older than age 30 years.