Background: Increased hypothalamic-pituitary-adrenal (HPA) axis activity manifested by elevated cortisol levels is observed in AD and may contribute to AD by lowering the threshold for neuronal degeneration. Presence of the APOE-epsilon4 allele increases risk for AD. Increased cortisol concentrations in apoE-deficient mice suggest that APOE genotype may influence cortisol concentrations in AD.
Methods: The authors measured cortisol levels in CSF and determined APOE genotypes for 64 subjects with AD and 34 nondemented older control subjects.
Results: CSF cortisol was significantly higher in AD than in control subjects. CSF cortisol concentrations differed with respect to APOE genotype in both subjects with AD (epsilon4/epsilon4 > epsilon3/4epsilon > epsilon3/epsilon3) and normal older control subjects (epsilon3/epsilon4 > epsilon3/epsilon3 > epsilon2/epsilon3). Comparison of CSF cortisol concentrations within the epsilon3/epsilon4 and epsilon3/epsilon3 genotypes revealed no differences between AD and control subject groups.
Conclusions: Higher CSF cortisol concentrations were associated with increased frequency of the APOE-epsilon4 allele and decreased frequency of the APOE-epsilon2 allele in AD subjects relative to control subjects. This effect of APOE genotype on HPA axis activity may be related to the increased risk for AD in persons carrying the APOE-epsilon4 allele and decreased risk for AD in persons carrying the APOE-epsilon2 allele.