| Summary: | Kaplan-Meier risk estimates were generated and evaluated for 1867 first-degree relatives of 338 Alzheimer Disease (AD) index cases and 1873 first-degree relativesof 351 non-cognitively impaired, non-demented elderly controls. A cumulative lifetime risk of 26.73 ± 4.42% for first-degree relatives of AD cases, while significantly higher than the cumulative lifetime risk of 7.26 ± 2.74% found for first-degree relatives of controls, does not suggest that all cases of AD are due to a single autosomal dominant gene(s), but is evidence that a genetic component to the etiologyof the disease exists. Female and male first-degree relatives of AD cases as well as parents and sibs of AD cases showed higher cumulative risks throughout their lifetimes when compared to their analogous control subgroups. Equal cumulative lifetime risks between first-degree female and male relatives (28.97 ± 3.60%, 22.03 ±8.29%) and between parents and sibs (27.67 ± 4.50%, 28.87 ± 8.92%) of AD cases, but significantly different lifetime risk curves suggest that non-genetic factors may affect the age-specific expression of AD in individuals with an identical genetic propensity. Equal risk between first-degree relatives of early-onset and late-onset AD cases does not support the suggestion that relatives of early-onset cases share a higher risk to develop the disease. These results are interpreted as being suggestive of a complex etiology with both genetic and environmental factors, as well as interactions between the two playing a role in AD expression.
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