When the aneurysms were classified according to location, size and WFNS grade and compared with different APOE genotype models and allele frequencies, only the PCOM aneurysm was statistically significant with ε2 vs. ε3 allele frequency (OR = 3.59, 95% CI = 1.11–11.64, p = 0.03). The gene discussed is APOE; the disease is aneurysm.