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Alternative splicing: a mechanism for phenotypic rescue of a common inherited defect

H Morisaki1, T Morisaki, L K Newby

  • 1Seymour Gray Molecular Medicine Laboratory, Department of Medicine, University of Pennsylvania, Philadelphia 19104-4283.

The Journal of Clinical Investigation
|May 1, 1993
PubMed

Insights

Genetic variations in the AMPD1 gene can cause metabolic myopathy. Alternative splicing of AMPD1 mRNA in skeletal muscle may correct this defect, explaining asymptomatic cases and symptom variability.

Area of Science:

  • Genetics
  • Molecular Biology
  • Biochemistry

Background:

  • A nonsense mutation in exon 2 of the AMPD1 gene affects 2% of Caucasians and African-Americans, leading to skeletal muscle AMP deaminase deficiency.
  • While over 100 patients exhibit symptoms of metabolic myopathy, many individuals with this defect remain asymptomatic, suggesting a compensatory mechanism.

Purpose of the Study:

  • To investigate the molecular basis for the "correction" of the genetic defect caused by AMPD1 mutations.
  • To explore the role of alternative splicing in the AMPD1 gene and its impact on AMP deaminase activity and clinical presentation.

Main Methods:

  • Analysis of AMPD1 mRNA transcripts in adult skeletal muscle and differentiating human myocytes.
  • Expression studies using AMPD1 mRNA lacking exon 2 to assess peptide functionality.
  • Transfection studies with human minigene constructs to identify regulatory signals for alternative splicing.

Main Results:

  • Alternative splicing, deleting exon 2, occurs in 0.6-2% of adult skeletal muscle AMPD1 mRNA transcripts.
  • AMPD1 mRNA lacking exon 2 encodes a functional AMP deaminase peptide.
  • Alternative splicing is significantly higher during in vitro myocyte differentiation and is regulated by tissue-specific and stage-specific signals.

Conclusions:

  • Alternative splicing of exon 2 in the AMPD1 gene provides a mechanism for phenotypic rescue in individuals with the inherited defect.
  • Variations in alternative splicing patterns may contribute to the observed variability in clinical symptoms among individuals with AMPD1 deficiency.

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