Apolipoprotein-E genotyping of diabetic dementia patients: Is diabetes rare in Alzheimer's disease?

OBJECTIVES: To determine whether diabetes is rare in Alzheimer disease (AD) relative to other types of dementia and whether diabetics with dementia have a low frequency of the Apolipoprotein-E E4 genotype. DESIGN: Observational survey study. SETTING: An Irvine, California, outpatient dementia assessment center. PARTICIPANTS: A total of 123 patients with AD, 51 with vascular dementia, 57 with ''mixed'' vascular dementia and AD, and 34 with ''other'' dementias (non-vascular non-AD). MEASUREMENTS: Demographic data; histories and evidence of diabetes, hypertension, heart disease, stroke; and Apolipoprotein-E genotype for 95 cases distributed across the groups. RESULTS: There were 15 diabetics in the sample (5.7%), all of whom had extensive vascular disease. Diabetes was rare in AD patients (0.8%) relative to vascular dementia (11.8%), mixed vascular/AD dementia (8.8%), and ''other'' dementia patients (8.8%). In addition, the E4 allele of apolipoprotein-E, associated with high risk for AD, was frequent in the AD group (71.4%), but in the diabetic group it was only as frequent as in the general population (38.5%). In the diabetics with E4, 60% (3/5) had mixed dementia. CONCLUSIONS: Diabetics with dementia rarely have AD except as a component of mixed dementia. Apo-E genotyping showed only average E4 allele frequency in diabetics compared with the high E4 frequency found in AD patients. However, mixed dementia in diabetics may be associated with the E4 allele, suggesting that close control of diabetes may be particularly important for those with E4 since they may be more likely than others to develop both diseases.