"Further to the wellestablished association between apolipoprotein E (APOE) and Alzheimer's disease, this gene has also been implicated in both susceptibility to, and dementia in, Parkinson's disease (PD). However studies to date have produced contradictory findings," scientists writing in the Journal of Neurology report (see also Dementia).

"We conducted a case-control study in a population of 528 PD patients and 512 healthy controls and found no significant difference in allele or genotype distribution of APOE between the two groups. An updated meta-analysis showed a modest increase of APOE-epsilon 2 carriers amongst PD patients compared to controls [P = 0.017, OR = 1.16 (95 % CI 1.03-1.31)]. 107 of our patients were incident cases participating in a populationbased epidemiological study. Longitudinal follow-up of this cohort over a mean of 5.0 +/- 0.7 years from diagnosis revealed no significant impact of APOE-epsilon 4 carrier status on risk of dementia or rate of cognitive decline. An updated meta-analysis indicated an over-representation of APOE-epsilon 4 carriers amongst PD dementia compared to non dementia cases [OR 1.74 (1.36-2.23), P = 1 x 10(-4)], although small sample sizes, heterogeneity of odds ratios and publication bias may have confounded this finding," wrote C.H. Williamsgray and colleagues, University of Cambridge.

The researchers concluded: "Our study does not support previously reported associations between APOE genotype and susceptibility to, or cognitive decline in, PD. An updated meta-analysis indicates any association with PD susceptibility is at most modest, an observation with important implications for further study of this issue. Large scale longitudinal studies would be best placed to further evaluate any impact of APOE genotype on cognitive decline in PD.."

Williamsgray and colleagues published their study in the Journal of Neurology (Apolipoprotein E genotype as a risk factor for susceptibility to and dementia in Parkinson's Disease. Journal of Neurology, 2009;256(3):493-498).

Additional information can be obtained by contacting C.H. Williamsgray, University of Cambridge, Dept. of Clinic Neuroscience, Cambridge Center Brain Repair, Forvie Site, Robinson Way, Cambridge CB2 2PY, UK.

The publisher of the Journal of Neurology can be contacted at: Dr. Dietrich Steinkopff Verlag, Tiergartenstrasse 17, 69121 Heidelberg, Germany.