GlcNAc is a circulating biomarker of advanced systemic mastocytosis (AdvSM). (A) Volcano plot of statistical significance against fold-change between the indolent and advanced forms of SM showing the most significantly differentially regulated metabolites linked to disease severity. (B) Plasmatic GlcNAc levels measured by LC-MS/MS in SM-related patients (n = 10, 5 ASM and 5 SM with associated hematological neoplasm [SM-AHN]), healthy donor (HD) (n = 5), allergic (n = 5), asthmatic (n = 5), acute leukemias (n = 9), chronic myeloid leukemia (CML; n = 10), myelodysplastic and myeloproliferative syndrome (MDS/MNP; n = 7), and essential thrombocythemia (ET) only (n = 10). (C) Receiver operating characteristic curve of GlcNAc concentrations between ISM and advanced SM patient samples. (D) GlcNAc and tryptase levels in SM patient samples. (E) Schematic representation of the hexosamine biosynthetic pathway (HBP) and the use of GlcNAc in the salvage pathway indicating relevant enzymes (O-linked-GlcNAc transferase [OGT], the O-GlcNAcase OGA, and GlcNAc kinase [NAGK]). (F) Lysates from 3 bone marrow biopsies from patients with MCAS, ISM, and AdvSM were immunoblotted with RL2 antibodies that detect O-GlcNAcylation (G) Quantification of the immunoblot shown in panel F by ImageJ software (National Institutes of Health). (H) Normalized transcript levels of HBP enzymes from microarray analysis performed in MCs sorted from bone marrow samples from HDs (n = 5) and patients presenting ISM (n = 14) or ASM (n = 12) disorders. The values in the graphs are presented as the means ± SD (NS [nonsignificant]; *P < .05, **P < .01, ***P < .001; 2-tailed, unpaired Student t test). AUC, area under the curve.