Diagnostic and therapeutic applications of the glycan biomarker H3N2b in GM1 Gangliosidosis.

GM1 gangliosidosis is a progressive lysosomal storage disorder caused by β-galactosidase deficiency, resulting in accumulation of GM1 ganglioside and related glycoconjugates. Current diagnostic approaches rely on enzymatic and genetic testing but do not provide dynamic measures of substrate accumulation or therapeutic response. The oligosaccharide H3N2b has previously been identified as a potential biomarker of impaired β-galactosidase activity. In this study, H3N2b was quantified in plasma, urine, and cerebrospinal fluid (CSF) from patients with GM1 gangliosidosis (n = 47 plasma/urine; n = 34 CSF) and age- and sex-matched controls using a validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay. A limited set of comparator lysosomal storage disorder samples was also analyzed to provide preliminary assessment of biomarker specificity. Longitudinal H3N2b measurements were obtained from participants receiving intravenous adeno-associated virus serotype 9 (AAV9)-mediated GLB1 gene therapy. H3N2b concentrations were significantly elevated in GM1 gangliosidosis compared with controls in plasma (cutoff 6.2 ng/mL; 100% sensitivity and specificity), urine (0.65 ng/μg creatinine; 99.3% sensitivity, 100% specificity), and CSF (5.1 ng/mL; 98.9% sensitivity, 100% specificity). H3N2b levels correlated with disease severity and were not influenced by age or sex. Among the comparator disorders analyzed, H3N2b values were generally below GM1 diagnostic cutoffs, although the comparator analysis was limited by sample availability and did not include several relevant disorders and CSF. In gene therapy recipients, plasma, urine, and CSF H3N2b concentrations decreased following treatment and closely paralleled changes in β-galactosidase activity, indicating pharmacodynamic responsiveness. These findings provide a cross-matrix clinical evaluation of H3N2b as a diagnostic and therapeutic biomarker for GM1 gangliosidosis and support its utility as a candidate biochemical biomarker to aid diagnosis and monitor treatment-associated biochemical changes.