Apolipoprotein E ε4 allele frequency is increased in Parkinson's disease only with co-existing Alzheimer pathology

We determined the apolipoprotein E (apoE) genotype in clinically diagnosed and neuropathologically verified cases of Parkinson's disease (PD) (n = 45), with or without Alzheimer (AD)-type changes, and compared the apoE genotype with that in healthy age-matched controls (n = 59). The PD cases were divided into two groups according to the CERAD criteria: "O + A", with no or only uncertain histological findings of AD, and "B + C" with histological findings suggestive or indicative of AD. DNA was isolated from frozen brain samples, and the apoE genotypes were determined using polymerase chain reaction amplification and subsequent restriction analysis by HhaI enzyme. The frequency of the apo epsilon 4 allele (29.4%) was significantly increased in the B + C group. The odds ratio for an apoe4 allele in the B + C group was 2.5 as compared to controls (95% confidence interval, 1.2-5.2). In the O + A group, the frequency of apo epsilon 4 allele (13.6%) was similar to that in controls (14.4%) and the risk of an apo epsilon 4 allele was not increased (odds ratio 0.94). The PD cases with an apoe4 allele had a greater number of cortical (P = 0.02) but not nigral Lewy bodies than those without an apoe4 allele (P = 0.57). The results show that neuropathologically verified PD as such is not associated with increased apoe4 allele frequency.