title: Skeletal muscle pathology of infantile Pompe disease during long-term enzyme replacement therapy.
abstract: BACKGROUND
  Pompe disease is an autosomal recessive metabolic neuromuscular disorder caused by a deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA). It has long been believed that the underlying pathology leading to tissue damage is caused by the enlargement and rupture of glycogen-filled lysosomes. Recent studies have also implicated autophagy, an intracellular lysosome-dependent degradation system, in the disease pathogenesis. In this study, we characterize the long-term impact of enzyme replacement therapy (ERT) with recombinant human GAA (rhGAA) on lysosomal glycogen accumulation and autophagy in some of the oldest survivors with classic infantile Pompe disease (IPD).
  
  
  METHODS
  Muscle biopsies from 8 [4 female, 4 male; 6 cross-reactive immunologic material (CRIM)-positive, 2 CRIM-negative] patients with a confirmed diagnosis of classic IPD were examined using standard histopathological approaches. In addition, muscle biopsies were evaluated by immunostaining for lysosomal marker (lysosomal-associated membrane protein-2; LAMP2), autophagosomal marker (microtubule-associated protein 1 light chain 3; LC3), and acid and alkaline ATPases. All patients received rhGAA by infusion at cumulative biweekly doses of 20-40 mg/kg.
  
  
  RESULTS
  Median age at diagnosis of classic IPD was 3.4 months (range: 0 to 6.5 months; n = 8). At the time of muscle biopsy, the patients' ages ranged from 1 to 103 months and ERT duration ranged from 0 (i.e., baseline, pre-ERT) to 96 months. The response to therapy varied considerably among the patients: some patients demonstrated motor gains while others experienced deterioration of motor function, either with or without a period of initial clinical benefit. Skeletal muscle pathology included fiber destruction, lysosomal vacuolation, and autophagic abnormalities (i.e., buildup), particularly in fibers with minimal lysosomal enlargement. Overall, the pathology reflected clinical status.
  
  
  CONCLUSIONS
  This is the first study to investigate the impact of rhGAA ERT on lysosomal glycogen accumulation and autophagic buildup in patients with classic IPD beyond 18 months of treatment. Our findings indicate that ERT does not fully halt or reverse the underlying skeletal muscle pathology in IPD. The best outcomes were observed in the two patients who began therapy early, namely at 0.5 and 1.1 months of age.
authors.forename: Sean N
authors.initials: SN
authors.lastname: Prater
authors.forename: Trusha T
authors.initials: TT
authors.lastname: Patel
authors.forename: Anne F
authors.initials: AF
authors.lastname: Buckley
authors.forename: Hanna
authors.initials: H
authors.lastname: Mandel
authors.forename: Eugene
authors.initials: E
authors.lastname: Vlodavski
authors.forename: Suhrad G
authors.initials: SG
authors.lastname: Banugaria
authors.forename: Erin J
authors.initials: EJ
authors.lastname: Feeney
authors.forename: Nina
authors.initials: N
authors.lastname: Raben
authors.forename: Priya S
authors.initials: PS
authors.lastname: Kishnani
mesh_terms: D056947:Enzyme Replacement Therapy; D005260:Female; D006009:Glycogen Storage Disease Type II / Q000188:drug therapy*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism / Q000473:pathology*; D000520:alpha-Glucosidases / Q000627:therapeutic use
chemical_list: C509951:GAA protein, human; D000520:alpha-Glucosidases