Figure 5a represents the MS spectrum of a feature with 972.4 m/z, which is upregulated in CKD patients and Fig. 5b represents its respective MS/MS fragmentation ion spectra, which is a fragment of amiloride-sensitive amine oxidase (AOC1, ABP1, DAO1) with the amino acid sequence of HYPRALCL. The gene discussed is AOC1; the disease is chronic kidney disease.