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 epsilon 4/epsilon 4 homozygosity an ApoE epsilon 4/epsilon 4 homozygous cohort was compared with an ApoE epsilon 3/epsilon 3 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 epsilon 3 and 133 were homozygous for ApoE epsilon 4, while 232 were heterozygous for ApoE epsilon 3/epsilon 4. Thirty patients in the entire sample were diagnosed with PD (4.8 %). In the ApoE epsilon 4/epsilon 4 group seven persons had PD (5.3 %), while in the ApoE epsilon 3/epsilon 3 comparison group nine persons were diagnosed with PD (3.5 %). In the ApoE epsilon 3/epsilon 4 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 epsilon 4 homozygous carriers. In comparison with the ApoE epsilon 3 homozygous carriers in our study, subjects who were homozygous for ApoE epsilon 4 demonstrated a slightly but statistically insignificant higher prevalence of PD, while in the ApoE epsilon 3/epsilon 4 heterozygous group we detected the highest rate of probands diagnosed with PD. We conclude that there is no correlation between allele combinations of ApoE epsilon 3 and ApoE epsilon 4 in their heterozygote and homozygote composition and prevalence of PD.