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Polyglucosan myopathy and functional characterization of a novel GYG 1 mutation
Author(s) -
HedbergOldfors C.,
Mensch A.,
Visuttijai K.,
Stoltenburg G.,
Stoevesandt D.,
Kraya T.,
Oldfors A.,
Zierz S.
Publication year - 2018
Publication title -
acta neurologica scandinavica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.967
H-Index - 95
eISSN - 1600-0404
pISSN - 0001-6314
DOI - 10.1111/ane.12865
Subject(s) - missense mutation , myopathy , muscle biopsy , muscle weakness , weakness , biology , atrophy , muscle atrophy , glycogen storage disease , glycogen debranching enzyme , exome sequencing , endocrinology , medicine , genetics , mutation , glycogen , glycogen synthase , anatomy , biopsy , gene
Objectives Disorders of glycogen metabolism include rare hereditary muscle glycogen storage diseases with polyglucosan, which are characterized by storage of abnormally structured glycogen in muscle in addition to exercise intolerance or muscle weakness. In this study, we investigated the etiology and pathogenesis of a late‐onset myopathy associated with glycogenin‐1 deficiency. Materials and methods A family with two affected siblings, 64‐ and 66‐year‐olds, was studied. Clinical examination and whole‐body MRI revealed weakness and wasting in the hip girdle and proximal leg muscles affecting ambulation in the brother. The sister had weakness and atrophy of hands and slight foot dorsiflexion difficulties. Muscle biopsy and whole‐exome sequencing were performed in both cases to identify and characterize the pathogenesis including the functional effects of identified mutations. Results Both siblings demonstrated storage of glycogen that was partly resistant to alpha‐amylase digestion. Both were heterozygous for two mutations in GYG 1 , one truncating 1‐base deletion (c.484delG; p.Asp163Thrfs*5) and one novel missense mutation (c.403G>A; p.Gly135Arg). The mutations caused reduced expression of glycogenin‐1 protein, and the missense mutation abolished the enzymatic function as analyzed by an in vitro autoglucosylation assay. Conclusion We present functional evidence for the pathogenicity of a novel GYG 1 missense mutation located in the substrate binding domain. Our results also demonstrate that glycogenin‐1 deficiency may present with highly variable distribution of weakness and wasting also in the same family.