Background
GM1 gangliosidosis is a rare, fatal, neurodegenerative disease caused by mutations in the GLB1 gene and deficiency in β-galactosidase. Delay of symptom onset and increase in lifespan in a GM1 gangliosidosis cat model after adeno-associated viral (AAV) gene therapy treatment provide the basis for AAV gene therapy trials. The availability of validated biomarkers would greatly improve assessment of therapeutic efficacy.
Methods
The liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to screen oligosaccharides as potential biomarkers for GM1 gangliosidosis. The structures of pentasaccharide biomarkers were determined with mass spectrometry, as well as chemical and enzymatic degradations. Comparison of LC-MS/MS data of endogenous and synthetic compounds confirmed the identification. The study samples were analyzed with fully validated LC-MS/MS methods. Findings: We identified two pentasaccharide biomarkers, H3N2a and H3N2b, that were elevated more than 18-fold in patient plasma, cerebrospinal fluid (CSF), and urine. Only H3N2b was detectable in the cat model, and it was negatively correlated with β-galactosidase activity. Following intravenous (IV) AAV9 gene therapy treatment, reduction of H3N2b was observed in central nervous system, urine, plasma, and CSF samples from the cat model and in urine, plasma, and CSF samples from a patient. Reduction of H3N2b accurately reflected normalization of neuropathology in the cat model and improvement of clinical outcomes in the patient. Interpretations: These