Incidence of Dementia in Very Elderly Individuals: A Clinical, Neuropathological and Molecular Genetic Study

AIMS: To evaluate the effect of medical record use on figures for the incidence of dementia and the effect of apolipoprotein E (APOE) polymorphism on this incidence and neuropathologically defined Alzheimer's disease (AD) in very elderly individuals. METHODS: Cognitive functions were examined in a cohort of 328 (92% of the very elderly people of a town participated in this study) nondemented Finnish elderly individuals 85 years of age or more in 1991. The examination was repeated in survivors in 1994, 1996, 1999 and 2001. Medical notes and social work records were evaluated. All these individuals were genotyped for APOE. Neuropathological analysis of AD-type pathology was performed on 159 of 303 subjects who died during the follow-up. RESULTS: Age group, gender or APOE did not significantly affect the incidence of dementia, which was over 20% higher (85 vs. 69 per 1,000 person-years) if the cognitive status at death was ascertained by medical and social work records than without this evaluation. The APOE upsilon4 allele was highly significantly (p=0.002) and age almost significantly (p=0.06) associated with neuropathological AD in nondemented individuals. CONCLUSIONS: Medical records should be analyzed in studies on the incidence of dementia in very elderly individuals. APOE polymorphism does not affect the incidence of dementia in this age group. However, clinical dementia diagnosis in very elderly individuals does not necessarily correlate well with the presence of neuropathological AD which, even in this age group, is significantly associated with the APOE upsilon4 allele.