Pompe disease is an autosomal recessive myopathic disorder arising from the deficiency of acid a-glucosidase (GAA). Autophagic buildup is a key factor for poor response to Enzyme replacement therapy in Pompe disease. This finding highlights the need for blood biomarkers which reflect autophagic dysfunction in skeletal muscles. In this study, we characterized the ubiquitin-protein conjugates in GAA-KO mouse plasma and skeletal muscles to investigate the possibility of them as a biomarker for autophagic buiidup. Skeletal muscle and plasma of GAA-KO and wildtype mice were lysed with 2% SDS and analyzed by using the antibodies against ubiquitin, K63-linked polyubiquitin, and LC3. Smears of ubiquitin-protein conjugates were more abundant in skeletal muscles of GAA-KO mice than those of wildtype mice. Additionally, the levels of specific ubiquitin-protein conjugates (approximately 58 kDa) were markedly increased in skeletal muscles of GAA-KO mice. Increased levels of the 58 kDa proteins were also observed in plasma from GAA-KO mice, and were prominently detected by anti-K63-linked polyubiquitin antibody. By immunohistological analysis, both LC3 and K63-linked ubiquitin-protein conjugates was colocalized in the myofibers from GAA-KO mice. These results suggest that the 58 kDa ubiquitin-protein conjugates in plasma may reflect the autophagic buildup in skeletal muscles from GAA-KO mice. Conflict of Interest declared. Background: N-linked oligosaccharides of glycoproteins represent important molecules that show significant alterations in a great number of conditions. Objectives: Given the fact that Pompe disease is characterized by altered glycogen metabolism, we hypothesized that N-glycan fingerprinting might represent a useful biomarker for the diagnosis and follow-up of Pompe patients. Patients and Methods: N-glycans in the serum of 2 patients with Pompe disease and an equal number of controls were isolated and digested with sialidase. The N-glycan profiles were analyzed by DNA sequencer-assisted fluorophore-assisted carbohydrate electrophoresis. Peaks corresponding to glycans were quantified and normalized to the total signal intensity. Results: We have found that the levels of profiles for peaks 1, 2, 4, 6, 7 and 9 displayed an increase, while those for peaks 3, 5 and 8 exhibited a decrease as compared to healthy controls. Peak 8, corresponding to a trigalactosylated, tri-antennary N-glycan structure (NA3), exhibited the most prominent difference, showing a 1.7-fold decrease. Measurements in consecutive blood samples before the initiation and during enzyme replacement therapy, showed no significant alterations in the concentrations of sugars. Conclusions: These data suggest that the changes in the serum N-glycans, especially NA3, could provide a useful biomarker for the diagnosis of Pompe patients. Background: Pompe disease (PD) is an autosomal recessive muscle disorder of glycogen metabolism caused by a deficiency of lysosomal alpha-glucosidase A (GAA) that results in the accumulation of glycogen primarily in muscle tissue leading to a severe hypertrophic cardiomyopathy associated with myopathy leading to death in early life. Objetive: We report a case of 8 months old baby affected by PD misdiagnosed as recurrent bronchiolitis episodes. Case report: Born of consanguineous parents (first cousin) without specific family history. He was admitted to hospital at 3, 4 and 5 months old affected by bronchiolitis; the last episode was associated to marked hypotonia. An echocardiography was performed and documented hypertrophic non obstructive cardiomyopathy and lab examinations showed a 3 fold increased CK levels. He was transferred to the regional centre of pediatric cardiology. Muscle biopsy suggested glicogen storage disease and blood spot revealed undetectable GAA activity. At 6 months of age he started enzyme replacement treatment in association of cardiac therapies and after 2 months the cardiac situation doesn't present any evolution. Conclusion: Respiratory disorder and progressive hypotonia could hide hypertrophic cardiomyopathy due to infantile PD form. The prognosis is strictly related to the early start of enzyme replacement treatment.