A total of 2,245 DNA samples were genotyped for APOE. Of these samples, 830 participants had a clinical diagnosis. No significant differences were seen in the frequency of the APOE genotypes between the clinically evaluated subjects and those without a clinical evaluation (p = 0.3898). However, the subjects with a clinical diagnosis are significantly older (73.9 ± 8.0 vs 73.0 ± 5.7; p = 0.0054), more likely to be female (71.8% vs 62.9%; p < 0.0001), and had no formal education (87.4% vs 84.2%; p = 0.0391). These differences were expected because there is oversampling of the poor performance group.
Of the 830 clinically evaluated subjects, 459 were normal and 140 were diagnosed with dementia (38 subjects at prevalence and 102 at incidence), of which 123 were diagnosed with AD (30 subjects at prevalence and 93 at incidence). The remaining 231 subjects were diagnosed with cognitive impairment and left out of the analyses. shows the baseline characteristics and APOE genotype and allele frequencies for subjects with each diagnosis. There was a significant difference in gender between both the demented and AD groups and normal subjects (demented vs normal: p = 0.0017; AD vs normal: p < 0.0001). Subjects with dementia and AD were significantly older than normal subjects (p < 0.0001 for both comparisons). In addition, the demented and AD groups contained less subjects who attended school (p = 0.0295 and 0.0075, respectively). All subjects were followed for similar amounts of time (demented vs normal: p = 0.1025; AD vs normal: p = 0.0637). Follow-up times for those with and without ε4 were similar (5.4 vs 5.2 years, respectively).
Baseline Characteristics and APOE Allele and Genotype Frequencies by Diagnosis
None of the APOE alleles were significantly increased in the AD (ε2: p = 0.6717; ε3: p = 0.3171; ε4: p = 0.1484) or dementia (ε2: p = 0.4878; ε3: p = 0.7226; ε4: p = 0.3586) groups compared with normal subjects. There were no significant differences in the distributions of the number of ε4 alleles between the AD (p = 0.3570) or demented (p = 0.6578) subjects and normal subjects.
Logistic regression results of the association of APOE with AD or dementia, after adjusting for gender, age at diagnosis, and education, are shown in . Again, there were no significant differences in the number of subjects with one or two copies of ε4 among the groups. In addition, the ε2 allele did not confer protection against the risk for dementia or AD. Gender and age at diagnosis were significant factors.
Logistic Regression Results on Dementia versus Normal Subjects and AD versus Normal Subjects by APOE genotype