Congenital myasthenic syndrome is a group of genetic disorders characterized by fatigable weakness of skeletal muscle that worsens with physical exertion with onset at or shortly after birth or in early childhood. Any of the skeletal muscles can be affected, most commonly facial and bulbar musculature, affecting sucking and swallowing, and leading to dysphonia. Other clinical features may include hypotonia (due to the axial and limb muscle weakness), ptosis and ophthalmoplegia (due to ocular muscles weakness). The diagnosis of CMS is based on clinical features and the treatment may be with AChE inhibitors and/or the potassium channel blocker 3,4-diaminopyridine (3,4-DAP)
Oystreck et al. (2011) reported five Saudi patients with genetically and pathology different ocular motility abnormalities involving straight eyes to describe the phenotypic similarity. The second patient was a 12-year-old boy with congenital myasthenic syndrome who developed bilateral ptosis and partial bilateral ophthalmoparesis at the age of 5 months. He had two older brothers affected with the same syndrome caused by a homozygous mutation in the CHRNE gene.