Characterization of monoclonal protein over the course of disease. Line graphs of measured serum M-spike (A) and λ FLC levels (B) in patient 1 at different testing time points. Diagnosis = 0 months; red point at 72 months is the bleeding time point.(C) Overlaid MALDI-TOF/MS LC [M +2H]²⁺ spectra of immunopurified IgG of patient 1 at diagnosis (upper panel) and bleeding (lower panel) time points. λLCs (vertical black lines) are of a greater mass than predicted normal range (dotted lines). Arrows show mass shifts from untreated IgG (black graph) to PNGase F–treated IgG (green graph), indicating the cleavage of N-linked glycan structures by PNGase F. (D) Deconvoluted λLC mass spectra generated by high-resolution MS of immunopurified IgG. Arrows point to sialylated and nonsialylated forms; 291 Da corresponds to SA.