title: The value of muscle biopsies in Pompe disease: identifying lipofuscin inclusions in juvenile- and adult-onset patients.
abstract: BACKGROUND
  Pompe disease, an inherited deficiency of lysosomal acid alpha-glucosidase (GAA), is a metabolic myopathy with heterogeneous clinical presentations. Late-onset Pompe disease (LOPD) is a debilitating progressive muscle disorder that can occur anytime from early childhood to late adulthood. Enzyme replacement therapy (ERT) with recombinant human GAA is currently available for Pompe patients. Although ERT shows some benefits, the reversal of skeletal muscle pathology - lysosomal glycogen accumulation and autophagic buildup - remains a challenge. In this study, we examined the clinical status and muscle pathology of 22 LOPD patients and one atypical infantile patient on ERT to understand the reasons for muscle resistance to ERT.
  
  
  RESULTS
  The patients were divided into three groups for analysis, based on the age of onset and diagnosis: adult-onset patients, juvenile-onset patients, and those identified through newborn screening (NBS). The areas of autophagic buildup found in patients' biopsies of all three groups, contained large autofluorescent inclusions which we show are made of lipofuscin, an indigestible intralysosomal material typically associated with ageing. These inclusions, analysed by staining, spectral analysis, time-resolved Fluorescence Lifetime Imaging (FLIM), and Second Harmonic Generation (SHG) imaging, were the major pathology remaining in many fibers after ERT. The best outcome of ERT both clinically and morphologically was observed in the NBS patients.
  
  
  CONCLUSIONS
  The muscle biopsy, in spite of its shortcomings, allowed us to recognize an underreported, ERT-resistant pathology in LOPD; numerous lysosomes and autolysosomes loaded with lipofuscin appear to be a hallmark of LOPD skeletal muscle. Lipofuscin accumulation - a result of inefficient lysosomal degradation - may in turn exacerbate both lysosomal and autophagic abnormalities.
authors.forename: Erin J
authors.initials: EJ
authors.lastname: Feeney
authors.forename: Stephanie
authors.initials: S
authors.lastname: Austin
authors.forename: Yin-Hsiu
authors.initials: YH
authors.lastname: Chien
authors.forename: Hanna
authors.initials: H
authors.lastname: Mandel
authors.forename: Benedikt
authors.initials: B
authors.lastname: Schoser
authors.forename: Sean
authors.initials: S
authors.lastname: Prater
authors.forename: Wuh-Liang
authors.initials: WL
authors.lastname: Hwu
authors.forename: Evelyn
authors.initials: E
authors.lastname: Ralston
authors.affiliation: Laboratory of Muscle Stem Cells and Gene Regulation, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD 20892, USA. kishn001@mc.duke.edu.
authors.forename: Priya S
authors.initials: PS
authors.lastname: Kishnani
authors.forename: Nina
authors.initials: N
authors.lastname: Raben
mesh_terms: D000328:Adult; D017668:Age of Onset; D001343:Autophagy / Q000502:physiology; D001706:Biopsy; D042241:Early Diagnosis; D005260:Female; D006009:Glycogen Storage Disease Type II / Q000473:pathology*; D006801:Humans; D002479:Inclusion Bodies / Q000378:metabolism / Q000473:pathology*; D008062:Lipofuscin / Q000378:metabolism*; D052119:Lysosomal-Associated Membrane Protein 2 / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000378:metabolism / Q000473:pathology*
chemical_list: D008062:Lipofuscin; D052119:Lysosomal-Associated Membrane Protein 2