The ϵ4 isoform of apolipoprotein E (Apo-E) may confer genetic susceptibility for familial and sporadic Alzheimer\u27s disease (AD). Because dementia in AD and Parkinson\u27s disease (PD) share many biologic and clinical features, we determined the Apo-E genotypes for 79 patients with PD, 22 of whom were demented, and for 44 age-matched healthy elderly controls from the same community. We hypothesized that if the dementia was similar to AD, there would be a higher allele frequency of apolipoprotein ϵ4 (Apoϵ4) in demented PD patients compared with nondemented PD patients and controls. The ϵ4 allele frequency for PD without dementia was 0.132, for PD with dementia, 0.068, and for controls, 0.102. There was no association between Apoϵ4 and dementia in the PD patients. We conclude that the biologic basis for dementia in PD may differ from that of AD
