APOE and Mental deterioration: One study of 505 patients with HGG, LGG, or meningiomas found that carriers of the APOE ε-4 allele (mean age 54.9 years, SD 13.9 years) did not have an increased risk of pre-treatment cognitive dysfunction or cognitive decline within one year of debulking surgery relative to non-carriers (mean age 55.3 years, SD 13.1 years) (150).