Disease Directory Slow-Channel Congenital Myasthenic Syndrome
Neuromuscular

Slow-Channel Congenital Myasthenic Syndrome

Also known as: slow-channel CMS, SCCMS, congenital myasthenic syndrome slow channel

Prevalence

Less than 1 in 500,000

Onset

Variable; infancy to adulthood (allelic heterogeneity)

Type

Autosomal dominant (gain-of-function)

Gene

CHRNA1, CHRNB1, CHRND, CHRNE

About Slow-Channel Congenital Myasthenic Syndrome

Slow-Channel Congenital Myasthenic Syndrome is caused by dominant gain-of-function mutations in genes encoding nicotinic acetylcholine receptor (AChR) subunits, prolonging channel open time and causing calcium-mediated excitotoxic damage to the end-plate and subsynaptic myonuclei. It is distinguished from other CMS subtypes by its dominant inheritance, characteristic end-plate myopathy on biopsy, and selective weakness of cervical, scapular, and finger extensor muscles. It is specifically treated with quinidine or fluoxetine, which shorten channel open time.

Common Clinical Features

Selective weakness of cervical and scapular muscles Finger extensor weakness Ptosis and ophthalmoparesis Fatigable weakness that worsens with activity Repetitive CMAP on single-nerve stimulation (electrodiagnostic hallmark) End-plate myopathy on muscle biopsy Variable bulbar involvement

Clinical Trial Eligibility Tips

What to know before applying to Slow-Channel Congenital Myasthenic Syndrome trials.

Genetic confirmation of a dominant pathogenic AChR subunit mutation is required; AChR antibodies are negative in CMS (differentiating it from myasthenia gravis) — confirm seronegative status in your records

Repetitive nerve stimulation (RNS) showing repetitive CMAP and single-fibre EMG showing increased jitter are key diagnostic electrophysiological findings required for most trials

Current medications including quinidine or fluoxetine may necessitate washout periods; discuss medication management with your neurologist well before a planned trial application

Patient Resources

Patient Organization

Myasthenia Gravis Foundation of America

Visit website ↗

Natural History Registry

CMS Registry (Congenital Myasthenic Syndrome)

Join registry ↗

Orphanet

European reference resource for rare diseases (ORPHA:99855)

View on Orphanet ↗

NORD

National Organization for Rare Disorders

Search NORD ↗

Find recruiting Slow-Channel Congenital Myasthenic Syndrome trials

Search 500,000+ studies from ClinicalTrials.gov, filtered for Slow-Channel Congenital Myasthenic Syndrome. Updated daily.

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