A large ApoE ε4/ε4 homozygous cohort reveals no association with Parkinson's disease

To investigate the correlation between cognitive impairment, Parkinson's disease (PD) symptoms and ApoE ε4/ε4 homozygosity an ApoE ε4/ε4 homozygous cohort was compared with an ApoE ε3/ε3 homozygous comparison group. A total of 696 outpatients with memory complaints had undergone comprehensive neuropsychiatric assessment including interview and examination by clinical psychiatrists and neurologists as well as laboratory blood testing (including ApoE genotyping). Patients also underwent the Consortium to Establish a Registry on Alzheimer's Disease (CERAD) test battery and the Clock-Drawing Test (Shulman scoring). Of the 623 selected individuals 258 were homozygous for ApoE ε3 and 133 were homozygous for ApoE ε4, while 232 were heterozygous for ApoE ε3/ε4. Thirty patients in the entire sample were diagnosed with PD (4.8 %). In the ApoE ε4/ε4 group seven persons had PD (5.3 %), while in the ApoE ε3/ε3 comparison group nine persons were diagnosed with PD (3.5 %). In the ApoE ε3/ε4 heterozygous group we found 14 (6.03 %) subjects meeting criteria for PD, P = 0.406. This is to our knowledge the largest retrospective cohort study to date of ApoE ε4 homozygous carriers. In comparison with the ApoE ε3 homozygous carriers in our study, subjects who were homozygous for ApoE ε4 demonstrated a slightly but statistically insignificant higher prevalence of PD, while in the ApoE ε3/ε4 heterozygous group we detected the highest rate of probands diagnosed with PD. We conclude that there is no correlation between allele combinations of ApoE ε3 and ApoE ε4 in their heterozygote and homozygote composition and prevalence of PD.