APOE and Cognitive impairment: [32] reported that average levels of CSF total tau and tau/Aβ42 ratio in participants with mild cognitive impairment (MCI) were higher in female APOE-ε4 carriers than male APOE-ε4 carriers; but in cognitively normal controls, they found no gender difference in either CSF Aβ42 or total-tau concentration, regardless of APOE genotype.