Dec. 1, 2000 ST. PAUL, MN – People with dementia are more likely to have had low scores on intelligence tests when they were children than people without dementia, according to a study in the November 28 issue of Neurology, the scientific journal of the American Academy of Neurology.
Late-onset dementia is defined as dementia that develops after age 64. The study found no link between childhood intelligence and early-onset dementia.
Several studies have suggested that environmental factors during childhood may contribute to the likelihood of developing dementia. But the relationship between childhood intelligence and dementia in later life hasn't been fully explored because few childhood intelligence test records are available for people who are old enough to have experienced the risk period for dementia, according to study author Lawrence Whalley, MD, of Aberdeen University in Aberdeen, Scotland.
This study relied on records from the Scottish Council for Research in Education of intelligence test scores of 87,498 children born in Scotland in 1921 who were tested at school in 1932. The researchers used medical records to find all 59 hospital-treated patients with early-onset dementia in Scotland from 1974 to 1988 who took the test in 1932. They also used public birth records to identify a comparison group of 118 people who took the test and had not developed early dementia. In addition, they identified all 892 people in Aberdeen City, Scotland, who were age 65 and had taken the test and compared test scores between the 50 who developed late-onset dementia and those who did not.
The study raises the question whether Alzheimer's disease is a developmental process beginning at conception or whether it is a disease acquired during the aging process, according to neurologist Richard Mayeux, MD, of Columbia University in New York, NY, who wrote an accompanying editorial on the study.
"If Alzheimer's disease is developmental, then the lower intelligence scores may reflect the earliest signs of the disease," Mayeux said. "This could then affect school performance, discouraging further schooling. These results may suggest that having less education is the result of Alzheimer's disease, not the cause of it. But there's not much evidence to support that view.
An alternative explanation is that people on the lower range of intelligence may be more vulnerable to Alzheimer's disease later in life, Mayeux said.
The question of when Alzheimer's disease begins is a challenge for researchers because there is no definitive biological marker for the disease, Mayeux said.
"Right now, when there is no way to prevent the disease, that question may seem moot," he said. "But if preventive therapies such as estrogen, anti-inflammatory agents and gingko biloba or the vaccine targeting amyloid accumulation prove to be effective, then the need to know when the disease starts will become crucial."
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