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Mutations in GMPPB Presenting with Pseudometabolic Myopathy

Chiara Panicucci1,2, Chiara Fiorillo2,3, Francesca Moro4

  • 1Center of Myology and Neurodegenerative Disorders, Department of Neuroscience and Rehabilitation, Istituto Giannina Gaslini, Genoa, Italy.

JIMD Reports
|May 1, 2017
PubMed

Insights

Mutations in the GMPPB gene cause muscular dystrophy with reduced alpha-dystroglycan. This study identifies new mutations in a patient with metabolic myopathy, expanding the known disease spectrum.

Area of Science:

  • Biochemistry
  • Genetics
  • Neurology

Background:

  • Mutations in the guanosine diphosphate mannose (GDP-mannose) pyrophosphorylase B (GMPPB) gene are linked to congenital (CMD) and limb girdle muscular dystrophy (LGMD).
  • These mutations affect the glycosylation pathway, leading to reduced alpha-dystroglycan (α-DG) in muscle biopsies.
  • Clinical presentations vary widely, from severe CMD to milder LGMD, sometimes with intellectual disability and epilepsy.

Purpose of the Study:

  • To investigate the genetic basis of a patient with a suspected metabolic myopathy and reduced α-DG.
  • To expand the understanding of the phenotypic spectrum associated with GMPPB gene mutations.

Main Methods:

  • Genetic analysis to identify mutations in the GMPPB gene.
  • Biochemical assays to assess α-DG glycosylation levels.
  • Clinical evaluation including muscle biopsy and creatine kinase (CK) level assessment.

Main Results:

  • Two missense mutations in the GMPPB gene were identified in a 21-year-old male patient.
  • The patient presented with elevated CK levels, myalgia, exercise intolerance, and myoglobinuria, mimicking metabolic myopathy.
  • Muscle biopsy revealed minimal changes, but a significant reduction in glycosylated α-DG was observed.

Conclusions:

  • This case broadens the known clinical and molecular spectrum of GMPPB-related disorders.
  • Highlights the importance of molecular genetic testing and assessing α-DG glycosylation in patients with unexplained myopathies.

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