Objective  To explore the association of APOE gene polymorphism with the brain function in the early stage of aneurysmal subarachnoid hemorrhage (SAH).   Methods  Totally 79 patients with aneurysmal SAH admitted in our hospital from March 2008 to April 2009 were recruited and their clinical data were collected. Electroencephalography (EEG) was recorded on admission and in 3 to 5 d after onset to assess the change of brain function of the patients in acute stage of SAH. The result of the second EEG recording was defined as EEG deterioration if the decrease in alpha wave frequency

increase in slow wave or decline in amplitude were observed when compared with the first EEG recording. The APOE polymorphism was determined by polymerase chain reactionrestriction fragment length polymorphism (PCR-RFLP).    Results  Ten of 17 patients with APOE ε4 (58.8%) showed the deteriorated EEG

which was significantly different from those without APOE ε4 (18 of 62 patients

29.0%

P=0.023). However

neither the presence of ε2 nor  of ε3 was significantly different from those absent of it (P0.05). Univariate logistic regression analyses showed that both high Fisher grade (P=0.028

OR=2.917

95% CI=1.124 to 7.572) and APOEε4 (P=0.027

OR=3.492

95% CI=1.150 to 10.604) were risk factors to EEG aggravation after aneurysmal SAH. The association of APOEε4 for deteriorated EEG was more significant after adjustment for age

gender

Hunt-Hess grade on admission

and Fisher grade (P=0.007

OR=5.741

95% CI=1.625 to 20.280).   Conclusion  Our findings suggest that the APOEε4  allele is a risk factor to brain function aggravation in the early stage of aneurysmal SAH

and it may contribute to early brain injury after SAH.