Relationship between apoE genotype and CSF β-amyloid (1–42) and tau in patients with probable and definite Alzheimer’s disease

We investigated the usefulness of cerebrospinal fluid (CSF) β-amyloid42 (Aβ42), β-amyloid40 (Aβ40) and tau analyses in the diagnosis of Alzheimer’s disease (AD). The study included 41 definite AD cases, 80 patients with probable AD, 27 with other dementias and 39 neurological controls. Aβ42, Aβ40 and tau protein concentrations in CSF were measured of using ELISA assays. Aβ42 levels were decreased and tau increased in AD. Combination of Aβ42 and tau resulted a sensitivity of 50.4% for AD and specificities of 94.8% for controls and 85.2% for other dementias. Ninety-one percent of the patients with Aβ42 below the cutoff value (340 pg/ml) and tau above the cutoff value (380 pg/ml) had AD. AD patients carrying apoE ε4 allele had lower Aβ42 (P < 0.005) and higher tau (P < 0.05) levels than those without an ε4 allele, and 18 (81.8%) of the 22 AD patients who had normal Aβ42 and tau levels were apoE ε4 allele non-carriers. Low Aβ42 and high tau concentration in CSF strongly support the diagnosis of AD. Measurement of Aβ42 may help the early diagnosis of cases at risk for AD such as apoE ε4 allele carriers.