Introduction: Pompe Disease (PD) is a lysosomal disorder caused by a deficiency of the enzyme acid alpha-glucosidase (GAA), primarily manifesting as a progressive myopathy with early respiratory involvement. Enzyme replacement therapy (ERT) is available since 2006., Materials and Methods: We describe 13 patients with partial GAA deficiency, followed at Hospital 12 de Octubre, 8 of whom were receiving treatment., Results: 8 patients exhibit symptoms, all with late onset. They display axial and proximal weakness predominantly in the lower limbs but maintain autonomous gait. Five patients require non-invasive mechanical ventilation due to respiratory insufficiency. All symptomatic patients receive ERT, and in 7/8 (87.5%), there is a decline in motor and pulmonary function after an average of 8.25 years of treatment (baseline and post-treatment FVC and 6MWT mean 86.6% vs 70.8% and 498 vs 430 meters, respectively)., Conclusion: Not all patients with partial GAA deficiency experience symptoms of PD, and symptomatic patients, despite ERT with recombinant alpha-glucosidase, mostly experience a gradual decline in motor and respiratory function., (Copyright © 2024 Elsevier España, S.L.U. All rights reserved.)