Late onset Alzheimer's disease (AD) is frequent in subjects who have reached an age above the average life expectancy. AD and life expectancy are both influenced by genetic factors. Consequently, a possible genetic relationship between AD and longevity was investigated using family study data.
First-degree relatives of patients with AD (n = 645) and of non-demented controls (n = 1,106) were examined by direct interview or by family history in the case of already deceased or unavailable subjects. Survival of subjects with an assumed familial load for AD (i.e. first-degree relatives of AD patients) and of controls was compared using the Kaplan-Meier analysis and log-rank statistics.
Relatives with AD reached higher ages than other family members. However, there was no significant co-aggregation of AD and longevity in first-degree relatives of AD patients in comparison with those of controls. This applied to all diseased as well as non-demented relatives.
Longevity is an independent prerequisite for the development of the disease, but is not genetically related to AD. The apparent longevity in relatives with AD is likely to result from the selection of subjects fulfilling this prerequisite.