Only 1 study has addressed CSF Klotho levels in patients with AD and found a similar decrease compared with controls.15 How Klotho is associated with progression of AD in the human brain remains unknown, but mouse studies suggest that Klotho modulates N-methyl-d-aspartate receptor function and activates microglia cells to promote cognitive function.28,29 We found significantly higher levels of CSF Klotho in KL-VS heterozygosity carriers in the control and AD-MCI groups but not the AD-dementia group. Here, KL is linked to Alzheimer disease.