Apolipoprotein E epsilon4 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 epsilon4 allele (29.4%) was significantly increased in the B + C group. The odds ratio for an apo epsilon4 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 epsilon4 allele (13.6%) was similar to that in controls (14.4%) and the risk of an apo epsilon4 allele was not increased (odds ratio 0.94). The PD cases with an apo epsilon4 allele had a greater number of cortical (P = 0.02) but not nigral Lewy bodies than those without an apo epsilon4 allele (P = 0.57). The results show that neuropathologically verified PD as such is not associated with increased apo epsilon4 allele frequency.