Case-control studies of Alzheimer’s disease were re-analysed to examine the association of Alzheimer’s disease with family history in first degree relatives of dementia, Down’s syndrome and Parkinson’s disease. Overall, the relative riskof Alzheimer’s disease for those with at least one first degree relative with dementia was 3.5 (95% confidence interval2.6-4.61. Stratification according to age of onset of Alzheimer’s disease showed that the relative risk decreased withincreasing onset age. However, among patients with an onset of disease after 80 years, there were still significantlymore subjects with one or more first degree relatives with dementia as compared to controls (relative risk 2.6; 95%confidence interval 1.3-5.2). The relative risk of Alzheimer’s disease was significantly lower in patients who had onefirst degree relative with dementia (relative risk 2.6; 95% confidence interval 2.0-3.5) as compared to those who hadtwo or more affected relatives (relative risk 7.5; 95% confidence interval 3.3-16.7). Furthermore, the re-analysisshowed a significant association between Alzheimer’s disease and family history of Down’s syndrome (relative risk2.7; 95% confidence interval 1.2-5.7), which was strongest in those patients who had a positive family history ofdementia. The relative risk of Alzheimer’s disease for those with a positive family history of Parkinson’s disease was 2.4(95% confidence interval 1.0-5.8).
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