title: Glycogen hyperphosphorylation underlies lafora body formation.
abstract: OBJECTIVE
  Glycogen, the largest cytosolic macromolecule, acquires solubility, essential to its function, through extreme branching. Lafora bodies are aggregates of polyglucosan, a long, linear, poorly branched, and insoluble form of glycogen. Lafora bodies occupy vast numbers of neuronal dendrites and perikarya in Lafora disease in time-dependent fashion, leading to intractable and fatal progressive myoclonus epilepsy. Lafora disease is caused by deficiency of either the laforin glycogen phosphatase or the malin E3 ubiquitin ligase. The 2 leading hypotheses of Lafora body formation are: (1) increased glycogen synthase activity extends glycogen strands too rapidly to allow adequate branching, resulting in polyglucosans; and (2) increased glycogen phosphate leads to glycogen conformational change, unfolding, precipitation, and conversion to polyglucosan. Recently, it was shown that in the laforin phosphatase-deficient form of Lafora disease, there is no increase in glycogen synthase, but there is a dramatic increase in glycogen phosphate, with subsequent conversion of glycogen to polyglucosan. Here, we determine whether Lafora bodies in the malin ubiquitin ligase-deficient form of the disease are due to increased glycogen synthase or increased glycogen phosphate.
  
  
  METHODS
  We generated malin-deficient mice and tested the 2 hypotheses.
  
  
  RESULTS
  Malin-deficient mice precisely replicate the pathology of Lafora disease with Lafora body formation in skeletal muscle, liver, and brain, and in the latter in the pathognomonic perikaryal and dendritic locations. Glycogen synthase quantity and activity are unchanged. There is a highly significant increase in glycogen phosphate.
  
  
  CONCLUSIONS
  We identify a single common modification, glycogen hyperphosphorylation, as the root cause of Lafora body pathogenesis.
authors.affiliation: Department of Genetics and Genome Biology, Hospital for Sick Children, Toronto, Ontario, Canada.
authors.forename: Julie
authors.initials: J
authors.lastname: Turnbull
authors.forename: Peixiang
authors.initials: P
authors.lastname: Wang
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Girard
authors.forename: Alessandra
authors.initials: A
authors.lastname: Ruggieri
authors.forename: Tony J
authors.initials: TJ
authors.lastname: Wang
authors.forename: Arman G
authors.initials: AG
authors.lastname: Draginov
authors.forename: Alexander P
authors.initials: AP
authors.lastname: Kameka
authors.forename: Nela
authors.initials: N
authors.lastname: Pencea
authors.forename: Xiaochu
authors.initials: X
authors.lastname: Zhao
authors.forename: Cameron A
authors.initials: CA
authors.lastname: Ackerley
authors.forename: Berge A
authors.initials: BA
authors.lastname: Minassian
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism; D002525:Cerebellar Cortex / Q000473:pathology / Q000648:ultrastructure; D004195:Disease Models, Animal; D054637:Dual-Specificity Phosphatases / Q000378:metabolism; D005786:Gene Expression Regulation / Q000235:genetics; D006003:Glycogen / Q000378:metabolism*; D006006:Glycogen Synthase / Q000235:genetics / Q000378:metabolism; D054559:Hyperphosphatemia / Q000209:etiology*; D002479:Inclusion Bodies / Q000378:metabolism*; D020192:Lafora Disease / Q000150:complications* / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D051379:Mice; D018345:Mice, Knockout; D018482:Muscle, Skeletal / Q000473:pathology* / Q000648:ultrastructure; D010710:Phosphates / Q000378:metabolism; D054558:Protein Tyrosine Phosphatases, Non-Receptor / Q000172:deficiency
chemical_list: D010710:Phosphates; D006003:Glycogen; D006006:Glycogen Synthase; D054637:Dual-Specificity Phosphatases; C491989:Epm2a protein, mouse; D054558:Protein Tyrosine Phosphatases, Non-Receptor