We then used this assay to qualitatively investigate plasma CLDN-5 levels in cognitively normal adults and patients with MCI or AD and considered the clinical implications of plasma CLDN-5 levels in AD from the point of view of correlations of plasma CLDN-5 levels with age and a phosphorylated tau protein (pTau-181), a biomarker of cognitive decline [7]. The gene discussed is CLDN5; the disease is Alzheimer disease.