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Novel truncating RAPSN mutations causing congenital myasthenic syndrome responsive to 3,4-diaminopyridine
Brenda L Banwell1, Kinji Ohno, Joern P Sieb
1Department of Pediatrics (Neurology), The Hospital for Sick Children, University of Toronto, Canada.
Neuromuscular Disorders : NMD
|March 24, 2004
Summary
Rapsyn deficiency causes congenital myasthenic syndromes, impacting acetylcholine receptor clustering. Genetic mutations in RAPSN lead to varied clinical severity and response to treatments like 3,4-diaminopyridine.
Area of Science:
- Neuromuscular junction physiology
- Genetic disorders of synaptic transmission
Background:
- Rapsyn is crucial for clustering acetylcholine receptors (AChRs) at the neuromuscular junction.
- Congenital myasthenic syndromes (CMS) can arise from defects in neuromuscular transmission.
Observation:
- Two children with CMS, lacking AChR subunit mutations, were found to have heterozygous recessive mutations in the RAPSN gene.
- Patient 1 had a frameshifting mutation, and Patient 2 had a nonsense mutation, alongside a known N88K mutation in both.
- Muscle biopsy in Patient 1 showed reduced AChRs and miniature endplate potential amplitude, consistent with rapsyn deficiency.
Findings:
- Both patients presented with congenital weakness, fatigability, and electromyography abnormalities.
- Clinical severity varied, with Patient 1 experiencing more severe symptoms including respiratory failure, contractures, and craniofacial malformations.
- Pyridostigmine offered partial benefit, while 3,4-diaminopyridine significantly improved clinical outcomes in both patients.
Implications:
- RAPSN mutations are a cause of CMS, demonstrating rapsyn's critical role in neuromuscular junction function.
- Genetic defects in rapsyn can lead to diverse clinical phenotypes, affecting symptom severity and associated complications.
- Targeted pharmacotherapy, particularly 3,4-diaminopyridine, shows promise for managing rapsyn deficiency-related CMS.