Congenital Myasthenic Syndromes (CMS)
Congenital myasthenic syndromes are a heterogeneous group of syndromes characterized by defects in neuromuscular transmission. These patients present in infancy or early childhood with fatiguable ocular and/or extremity weakness. Ocular manifestations include ptosis, orbicularis weakness and strabismic deviations.
These disorders are distinguishable from myasthenia gravis (MG) in the etiology of the transmission defect; while the transmission defect in MG is caused by antibodies against the acetylcholine receptor, CMS is caused by genetic presynaptic, synaptic, or postsynaptic defects at the neuromuscular junction. The inheritance of these syndromes can be autosomal dominant or recessive. Initial therapy is usually medical and tailored to the exact neuromuscular deficiency. Surgical correction of ptosis is reserved for those cases that do not respond to medical therapy (Sieb 2002).