Rapsyn mutations in hereditary myasthenia: distinct early- and late-onset phenotypes

Area of Science:

• Neurology
• Genetics
• Molecular Biology

Background:

• Congenital/hereditary myasthenic syndromes (CMS) are rare neuromuscular disorders.
• Rapsyn is crucial for neuromuscular junction formation and function.
• Genetic mutations in rapsyn can lead to CMS, but specific mutation spectra and associated phenotypes require further elucidation.

Purpose of the Study:

• To identify genetic mutations in rapsyn in patients with congenital/hereditary myasthenic syndrome.
• To characterize the clinical phenotypes associated with identified rapsyn mutations.
• To investigate a specific common mutation and its implications for diagnosis and treatment.

Main Methods:

• Genetic sequencing of the rapsyn gene in 16 unrelated patients with CMS.
• Clinical data collection and phenotyping of affected individuals.
• Analysis of mutation-specific clinical presentations and outcomes.

Main Results:

• Rapsyn mutations were identified in 16 unrelated patients.
• A common mutation, N88K, was found in all patients.
• Two distinct phenotypes were observed: early-onset (often with arthrogryposis multiplex congenita and crises) and late-onset (initially misdiagnosed as seronegative myasthenia gravis).

Conclusions:

• Rapsyn mutations, particularly N88K, are a significant cause of congenital/hereditary myasthenic syndrome.
• The N88K mutation presents with diverse phenotypes, including a late-onset form mimicking other myasthenic conditions.
• Recognition of these rapsyn-associated phenotypes is critical for accurate diagnosis and to avoid inappropriate immunotherapy.