Vacuolated PAS‐positive lymphocytes as an hallmark of Pompe disease and other myopathies related to impaired autophagy

Autosomal recessive Pompe disease is a lysosomal disorder caused by mutations of the acid‐α‐glucosidase (GAA) gene. Deficiency of GAA enzyme leads to glycogen accumulation and autophagy impairment in cardiac and skeletal muscles, but also in lymphocytes. Since an effective therapy is available, a rapid, sensitive, and specific test is crucial to early identify affected subjects. Number of lymphocytes containing PAS‐positive vacuoles was evaluated on blood films from 72 consecutive adult patients with hyperckemia and/or muscle weakness, 13 genetically confirmed late‐onset‐Pompe‐disease (LOPD) and 13 of their offspring. GAA activity, measured on dried blood spot (DBS) in all patients inversely correlated with number of PAS‐positive lymphocytes. More than 4 PAS‐positive lymphocytes were found in 11 out of the 72 patients (6 new diagnosis of LOPD, 3 different glycogen storage myopathies, 1 glucose‐6‐phosphate dehydrogenase deficiency, 1 caveolinopathy), in all 13 LOPD patients and in the 13 LOPD offspring. These latter resulted to have all a single GAA mutation but low GAA levels. Immunostaining with the autophagy markers LC3 and p62 confirmed the autophagic nature of lymphocytes vacuoles. ROC curve assessment of PAS‐positive lymphocytes disclosed 100% of sensitivity and 94% of specificity in recognizing both compound heterozygous and heterozygous GAA carriers. The other myopathies with more than 4 PAS‐positive lymphocytes appeared to be all related to impaired autophagy, which seems to be responsible of PAS‐positive vacuolated lymphocytes formation. Quantification of PAS‐positive lymphocytes in blood films is useful to identify autophagic vacuolar myopathies and should be routinely used as first level test for Pompe disease. Deficiency of the lysosomal acid‐α‐glucosidase enzyme leads to autophagy impairment and glycogen accumulation in Pompe disease. Assessment of PAS‐positive autophagic vacuoles in lymphocytes on blood smears, is a highly sensitive and specific method to discern Pompe patients from other neuromuscular disorders, and, in a broader sense, to identify conditions of “impaired autophagy” even in asymptomatic subjects.