A meta-analysis of prospective cohort studies demonstrated that advanced age, age at PD onset, PIGD, rapid eye movement sleep behavior disorder, hallucinations, orthostatic hypotension, anxiety, APOE ε2, APOE ε4, and EEG theta power > median and alpha power < median were statistically significantly associated with NCI [31]. The gene discussed is APOE; the disease is Parkinson disease.