Myasthenic Syndrome, Congenital, 21, Presynaptic, also known as congenital myasthenic syndrome 21, is related to myasthenic syndrome, congenital, 2c, associated with acetylcholine receptor deficiency and fetal akinesia deformation sequence 1. An important gene associated with Myasthenic Syndrome, Congenital, 21, Presynaptic is SLC18A3 (Solute Carrier Family 18 Member A3), and among its related pathways/superpathways are 10q11.21q11.23 copy number variation syndrome and Sympathetic Nerve Pathway (Pre- and Post- Ganglionic Junction). Affiliated tissues include skeletal muscle and heart, and related phenotypes are ptosis and ophthalmoplegia