We determined the prevalence of dementia in a cohort of 2494 elderly Nigerians residents in Idikan Community, Ibadan, Nigeria. We utilized the Community Screening Instrument for Dementia to select subjects for clinical assessment in the second stage. The findings were compared with those of 2212 African Americans living in Indianapolis, studied simultaneously using similar methodology. The overall age-adjusted prevalence rates of dementia and Alzheimer's disease in Ibadan were 2.29% and 1.41%, respectively. These rates were much lower than the respective values of 8.24% and 6.24% obtained for African Americans. In Ibadan, Alzheimer's disease accounted for 64.3% of the cases, with old age and female gender being the significant risk factors, whilst 'living with others' appeared to be protective (P < 0.05). Amongst African Americans, on the other hand, old age, rural living below the age of 19 years, low educational attainment and family history of dementia were the risk factors. There was a lack of association between Alzheimer's disease and possession of the apolipoprotein E epsilon4 allele in the Nigerian sample, unlike the finding in African Americans, where significant association was shown. In addition, the frequencies of the vascular risk factors investigated were lower in Nigerians. Our results showed lower prevalence of dementia and Alzheimer's disease in Nigerians, compared with African Americans. There was no association between Alzheimer's disease and apolipoprotein E (epsilon4 allele) in the former. The differences in the frequencies of vascular risk factors between Nigerian subjects and African Americans would suggest involvement of environmental factors in disease process.

As part of a community-based study of Alzheimer's Disease (AD) in a Nigerian population aged 65 years and over, we have determined apolipoprotein E (APOE) genotypes on 56 subjects (39 controls and 17 subjects with dementia, including 12 with AD). The epsilon 4 allele of APOE was not associated with AD or dementia in this community-based sample. The epsilon 4 allele frequency was 17.6% in demented patients and 16.7% in AD patients compared with 20.5% in the control subjects. These findings are in marked contrast to the strong association between the epsilon 4 allele and AD in our previously reported study with African Americans.

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