Relationship between serum metabolites, clinical diagnosis, and Aβ1–42 status. Serum PC ae 44:4 (A), PC ae 44:4 (B), and C18 (C) concentrations stratified by clinical diagnosis and CSFAβ1–42–defined groups. The concentration of each metabolite is shown for each diagnosis red: CN, green: MCI, blue: AD and by N. Abeta: normal concentrations of Aβ1–42 (>192 pg/mL), and Path. Abeta: pathological concentrations of Aβ1–42 (<192 pg/mL), Y-axes are values for each metabolite. Scatter plot for ADAS-Cog13 and serum valine values (D). Black line and shading are the regression line and 95% confidence interval. (D and E) Correlations between valine levels and cognitive decline in ADNI-1 and Rotterdam, respectively. Abbreviations: α-AAA, α-Aminoadipic acid; ADAS-Cog13, Alzheimer’s Disease Assessment Scale–Cognition; ADNI-1, Alzheimer’s Disease Neuroimaging Initiative–1; C0, free carnitine; Cx:y, acylcarnitines; Cx:y-OH, hydroxylacylcarnitines; Cx:y-DC, dicarboxylacylcarnitines; lysoPC, lyso-glycero-phosphatidylcholines (a = acyl); PC, glycero-phosphatidylcholines (aa = diacyl, ae = acyl–alkyl); SDMA, symmetric dimethylarginine; SMx:y, sphingomyelins; SM (OH) x:y, N-hydroxylacyloylsphingosyl-phosphocholine; T4-OH-Pro, trans-4-hydroxyproline.