Effects of short-to-long term Enzyme Replacement Therapy (ERT) on skeletal muscle tissue in Late Onset Pompe disease (LOPD)

AIMS: Pompe disease is an autosomal recessive lysosomal storage disorder resulting from deficiency of acid α-glucosidase (GAA) enzyme. Histopathological hallmarks in skeletal muscle tissue are fiber vacuolization and autophagy. Since 2006, ERT is the only approved treatment with human recombinant GAA alglucosidase alfa. We designed a study to examine ERT-related skeletal muscle changes in 18 modestly to moderately affected LOPD patients along with the relationship between morphological/biochemical changes and clinical outcomes. Treatment duration was short-to-long term. METHODS: We examined muscle biopsies from 18 LOPD patients at both histopathological and biochemical level. All patients underwent two muscle biopsies, before and after ERT administration respectively. The study is partially retrospective because the first biopsies were taken before the study was designed whereas the second biopsy was always performed after at least six months of ERT administration. RESULTS: After ERT, 15 out of 18 patients showed improved 6MWT (p=0.0007) and most of them achieved respiratory stabilization. Pre-treatment muscle biopsies disclosed marked histopathological variability, ranging from an almost normal pattern to a severe vacuolar myopathy. After treatment, we detected morphological improvement in 15 patients and worsening in 3 patients. Post-ERT GAA enzymatic activity was mildly increased compared with pre-treatment levels in all patients. Protein levels of the mature enzyme increased in 14 of the 18 patients (mean increase = +35%; p<0.05). Additional studies demonstrated an improved autophagic flux after ERT in some patients. CONCLUSIONS: ERT positively modified skeletal muscle pathology as well as motor and respiratory outcomes in the majority of LOPD patients. This article is protected by copyright. All rights reserved.